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  • 1995-1999  (403)
  • 1998  (164)
  • 1997  (239)
  • Analytical Chemistry and Spectroscopy  (375)
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  • 1995-1999  (403)
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  • 101
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 519-522 
    ISSN: 0935-6304
    Keywords: Supercritical Fluid Extraction (SFE) ; Micellar Eletrokinetic Capillary Chromatography (MEKC) ; Diuron ; sugar cane ; orange ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 102
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 509-512 
    ISSN: 0935-6304
    Keywords: Cholesterol oxidation ; gas chromatography ; oxysterols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The performance of a fused silica column coated with 50% phenyl-/50% dimethyl-polysiloxane, characterized by a high thermal stability, was evaluated for the gas chromatographic determination of cholesterol oxidation products. A silylated mixture of eighteen oxysterol standards (0.1 mg/ml of each compound) was injected into the gas chromatographic system. The temperature was programmed from 230 to 260°C at 2.5°/min and then to 290°C at 1°/min; the injector and detector temperatures were set at 325°C, and the gas linear velocity was 22.8 cm/s. The column gave a fast (15 min) and satisfactory resolution of the main cholesterol oxides. Good separation of the hydroxy from the epoxy derivatives was achieved.The suitability of the method for the determination of oxysterols in food matrices was successfully tested on a saponified lipid extract from egg yolk powder, previously enriched and purified by NH2 solid phase extraction.
    Additional Material: 3 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 531-539 
    ISSN: 0935-6304
    Keywords: gas chromatography ; carrier gas flow ; loss modified Poiseuille flow ; hold-up times ; peak widths ; velocity profiles ; permeability of helium through fused silica ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Hold-up times and peak widths have been measured in long fused silica GC capillary columns at high temperature with helium as the carrier gas. The results lead to the conclusion that the helium permeates through the column walls. The conventional Poiseuille theory of carrier gas flow has been extended to include this phenomenon. The resulting “loss modified Poiseuille” model, which uses literature values for the permeability of fused silica to helium, has been used to simulate the observed behavior. Good agreement between simulation and experiment validates the model. Simulations have been used to explore the effect of column permeability on hold-up times, peak widths, and velocity profiles over a broad range of column geometries.
    Additional Material: 5 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 549-553 
    ISSN: 0935-6304
    Keywords: Hydroxytyrosol ; GC-MS ; wine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Hydroxytyrosol (HTy) is a potent natural antioxidant found in olive oil and in mill waste waters. Although wines are rich in polyphenols, hydroxytyrosol has not been identified in wines so far. We have analyzed ten wines from different grape varieties grown in several Italian regions, using a gas-chromatograph coupled to a mass selective detector (GC-MS). Solid-phase extraction of wine samples was performed on a C18 column, with ethyl acetate used as eluting agent. Eluates were derivatized with bis(trimethylsilyl)trifluoroacetamide (BSTFA) and analyzed by GC-MS using one target and two qualifying ions. The detection limit was 15 pg/μL, with 49% average recovery. Under these experimental conditions hydroxytyrosol was detected in all wines analyzed. Its average concentrations in red and white wines were 4.0 mg/L and 1.9 mg/L, respectively.
    Additional Material: 3 Ill.
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  • 105
    ISSN: 0935-6304
    Keywords: Ligand-exchange chromatography ; dodecyl-norephedrine ; enantiomeric separation ; amino alcohol ; coating ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Underivatized aliphatic β-amino alcohols with a primary or secondary alcohol moiety were separated into enantiomers by high performance liquid chromatography using octadecylsilanized silica coated with N-n-dodecyl-(1R,2S)-norephedrine as the stationary phase and an aqueous solution containing copper(II) and barbital as the mobile phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 106
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 554-560 
    ISSN: 0935-6304
    Keywords: LC stationary phases ; octadecyl and octylsilica characterization ; cyclodextrins ; partially methylated cyclodextrins ; heptakis(2,6-di-O-methyl)-β-CD ; evaporative light scattering detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In order to establish guidelines to help the analyst in the choice of the most suitable octadecyl or octyl bonded phase for the LC analysis of a given partially methylated β-CD sample, analyses of four commercially available dimethyl-β-cyclodextrins (DM-β-CDs) have been carried out on nine octyl (C8) or octadecyl (C18) silica bonded or polymeric bonded phases which differ significantly in their hydrophilic and hydrophobic properties. Chromatograms show that the nature of the packing materials has considerable influence on the resolution of complex mixtures composed of closely related compounds such as partially methylated β-CDs. Among various kinds of C8 and C18 bonded phases, silica based and monomeric phases which present both reinforced hydrophobic and polar interactions showed the best performance. Whatever the complexity of the commercial DM-β-CD, the richest chromatographic fingerprints, which best depict the complexity of the mixture, are obtained with Nucleosil 50-5-C8 column. For the simplest mixtures, Nucleosil 50-5-C8 column with acetonitrile-water (34:66) as mobile phase is the most suitable chromatographic system and leads to the best resolution between heptakis (2,6-di-O-methyl)-β-CD and hexakis (2,6-di-O-methyl)-mono(2,3,6-tri-O-methyl)-β-CD (14 OCH3 and 15 OCH3). This chromatographic system might enable an LC-MS coupling for direct identification of the different components in the mixture as well as control of batch to batch variations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 107
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 565-568 
    ISSN: 0935-6304
    Keywords: capillary gas chromatography ; precalculation of retention indices ; boiling points ; two- and multidimensional taxonomic groups of organic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---It was shown that reciprocally unambiguous conformity between GC retention indices (at least for the commonly used standard nonpolar polydimethylsiloxane liquid phases) and boiling points of organic compounds is typical not only within one-dimensional taxonomic groups (homologous series and/or groups of congeners), but also within two- and multidimensional taxonomic groups (with simultaneous variations of some structural fragments). In all cases, this conformity is described by three-parameter non-linear equations log RI = a log Tb + b (n1 + Σ ki ni) + c, where n1 is the serial number of homologue within corresponding series and ni is the number of other structural fragments in the molecules. The coefficients ki in this equation reflect the relative alterations of molecular polarizabilities and may be estimated as ratios of refractions ki = RD(X)/RD(CH2), where X are variable structural fragments within a group of congeners, RD(CH2) = 4.647 cm3mol-1. The approach under discussion permits precalculation of the retention indices of any organic compounds with known boiling points. The precision of proposed method of RI precalculation is comparable with the contemporary level of interlaboratory reproducibility of experimental RI determination with standard nonpolar liquid phases (5-10 i.u.).
    Additional Material: 1 Tab.
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  • 108
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 583-586 
    ISSN: 0935-6304
    Keywords: Fast gas chromatography ; narrow-bore columns ; flash-2D-GC ; dedicated fast GC instrumentation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Savings in analysis time in capillary GC have always been an important issue for chromatographers since the introduction of capillary columns by Golay in 1958. In laboratories where gas chromatographic techniques are routinely applied as an analytical technique, every reduction of analysis time, without significant loss of resolution, can be translated into a higher sample throughput and hence reduce the laboratory operating costs. In this contribution, three different approaches for obtaining fast GC separations are investigated. First, a narrow-bore column is used under conventional GC operating conditions. Secondly, the same narrow-bore column is used under typical fast GC conditions. Here, a high oven temperature programming rate is used. The third approach uses a recent new development in GC instrumentation: Flash-2D-GC. Here the column is placed inside a metal tube, which is resistively heated. With this system, a temperature programming rate of 100°/s is possible. The results obtained with each of these three approaches are compared with results obtained on a column with conventional dimensions. This comparison takes retention times as well as plate numbers and resolution into consideration.
    Additional Material: 4 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 592-596 
    ISSN: 0935-6304
    Keywords: capillary gas chromatography ; new chiral selectors anchored to polysiloxane ; t-leucine derivatives ; immobilization ; radical-induced cross-linking ; low racemization of the phases ; high enantioselectivity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---New chiral polysiloxanes have been prepared as stationary phases for gas chromatography, with (S)-(-)-t-leucine-t-butylamide, (S)-(-)-t-leucine-(S)-(-)-1-phenylethylamide, (S)-(-)-t-leucine-(S)-(-)-1-(α-naphthyl)ethylamide, (S)-(-)-t-leucine-(R)-( + )-1-phenylethylamide, and (S)-(-)-t-leucine-(R)-( + )-1-(α-naphthyl)ethylamide as selectors. Immobilization is achieved by radical-induced cross-linking with 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4) and dicumyl peroxide (DCUP) as cross-linking reagents and cured at 170°C. Under these conditions, racemization of (S)-(-)-t-leucine is less than 4.5% (R) for 1 h curing, while for polysiloxanes with the conventional (S)-(-)-valine selectors about 20% of R-enantiomers are formed by racemization. In the presence of 5% (w/w) V4 and 6% of DCUP with regard to the phases, 70-80% immobilization is achieved; without V4, the degree of immobilization is about 50% for both the (S)-(-)-t-leucine and (S)-(-)-valine selectors. As the size of the amide moieties of the selectors increases from t-butyl to 1-(α-naphthyl)ethyl, the degree of immobilization decreases. If the curing time is prolonged to 2 h, the extent of racemization increases. The selectivity factors achieved for amino acid enantiomers and similar pharmaceuticals are generally higher than those obtained with the corresponding non-immobilized Chirasil-Val phases.
    Additional Material: 3 Ill.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 620-622 
    ISSN: 0935-6304
    Keywords: Multidimensional gas chromatography ; comprehensive two-dimensional gas chromatography ; kerosene analysis ; cryogenic modulation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 617-619 
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; cellulose acetate fiber ; microcolumn liquid chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 112
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 613-616 
    ISSN: 0935-6304
    Keywords: Micro LC ; FID detection ; superheated water ; alcohols ; aldehydes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In the current study, an HPLC-FID system using superheated water as the eluent is constructed and further improved. Signal stability during temperature programmed operation was improved by using separate thermostatting of the 50 μm capillary restrictor. Operating the restrictor at 75°C prevented the superheated water from sputtering in the restrictor. Conventional octadecyl-modified silica, thermostable polymeric reversed phase and carbon type HPLC columns were used. The feasibility of the system is demonstrated by the analysis of a variety of compounds such as alcohols and aldehydes. It is shown that increased temperatures decrease elution times and, in addition to this, frequently improve peak shapes and column efficiencies. The separation of lower aldehydes is performed at 175°C with a detection limit in the low μg/ml range. The possibility of temperature programming is demonstrated for the separation of a range of alcohols. Furthermore, it is shown that temperature programming can be used for sample enrichment. Large volume injection with low temperature enrichment resulted in good peak shapes and a significant improvement of the detection limit. In this way, detection limits of 0.2 μg/ml (ppm) could be obtained for the aldehydes studied. Finally, the possibilities of using mobile phase additives as, e.g., buffers were briefly examined.
    Additional Material: 5 Ill.
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  • 113
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 623-624 
    ISSN: 0935-6304
    Keywords: Sulfur compounds ; waste paper ; chemiluminescence detector ; food packaging ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 114
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 640-644 
    ISSN: 0935-6304
    Keywords: chiral separation ; uncharged and charged cyclodextrin ; borate complexation ; capillary electrophoresis ; propranolol and its metabolites ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A buffer system of borate with charged (carboxymethyl-β-CD) and uncharged (β-CD) cyclodextrins (CDs) was employed in the chiral resolution and separation of propranolol and its selected major metabolites. By appropriate choice of buffer and additive conditions, chiral resolution of all of the compounds studied was achieved in a single analysis, where near baseline resolution was found for the difficult to resolve propranolol-glycol (Pr-glycol). This has not been observed in previous studies of propranolol and its metabolites.
    Additional Material: 9 Ill.
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  • 115
    ISSN: 0935-6304
    Keywords: gas chromatography (GC) ; nitrogen-phosphorus detection (NPD) ; sorptive extraction/thermal desorption (SE/TD) ; amines ; in-situ derivatization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The use of sorptive extraction/thermal desorption (SE/TD) for the enrichment of amines from aqueous samples was investigated. The amines were derivatized in situ in the water sample by pentafluorobenzoyl chloride and subsequently enriched onto the SE cartridge. Two SE/TD cartridges were used, a commercially available polydimethylsiloxane (PDMS) packed cartridge and a similar cartridge prepared with newly synthesized poly(butyl acrylate) (PBA). Blank profiles of PBA were not as good as those obtained from the PDMS phase. A complex chromatogram was obtained using mass spectrometric detection. Fortunately, the use of a nitrogen-phosphorus detector (NPD) resulted in clean blanks. The PBA phase showed superior performance for the enrichment of the polar amine derivatives from water samples compared to the PDMS material. Using a CGC-NPD set-up and only 1 mL samples, detection limits are in the sub-ppb range.
    Additional Material: 2 Ill.
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  • 116
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 661-664 
    ISSN: 0935-6304
    Keywords: SPME ; AED ; metazachlor ; pesticides ; waste water ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 117
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 658-660 
    ISSN: 0935-6304
    Keywords: 1,3-Dioxolanes ; acetals ; ketals ; coffee-like flavorings ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper concerns a number of commercially available coffee-like flavoring preparations, identifying certain dioxolane structures of particular interest. The research was carried out by GC/MS, and spectral characterization was performed of the compounds in question, and especially of the acetals and ketals produced from compounds with carbonyl functions and 1,2-propylene glycol. Some determinations by means of chiral gas chromatography and by Isotope Ratio Mass Spectrometry (IRMS) have been useful in improving the analytical characterization of certain dioxolanes.
    Additional Material: 2 Ill.
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  • 118
    ISSN: 0935-6304
    Keywords: PAHs ; on-line SPE ; disk extraction ; RPLC ; water ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 119
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 32-38 
    ISSN: 0935-6304
    Keywords: LMCS ; column bleed ; modulation ; signal enhancement ; capillary GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A Longitudinally Modulated Cryogenic System (LMCS) was evaluated for its use in detection enhancement in capillary gas chromatography. The mechanism for chromatographic re-elution for the LMCS is substantially different to other cryogenic devices. The cooled region of the capillary column in which chromatographic bands may be focused is heated by the surrounding oven temperature either by moving the trap along the column, or by moving the column out of the trap. By continually modulating the LMCS at the detector end of the capillary column, signal-to-noise ratios of routine chromatograms can be readily increased by a factor of ten, thus enhancing chromatographic detection. Base widths of peaks, which are often about 2-3 s or more can be easily reduced to 0.3 s when the LMCS is employed in the detection enhancement mode, thus offering a simple avenue to improved peak height sensitivity in capillary gas chromatography.
    Additional Material: 7 Ill.
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  • 120
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 47-54 
    ISSN: 0935-6304
    Keywords: multidimensional gas chromatography ; comprehensive two-dimensional gas chromatography ; GC×GC ; characterization of petroleum samples ; quantitative analyses ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A software program was developed to enable the quantification of the complex 3D-data sets as produced by GC×GC. Using this software, it was demonstrated that the detectability limit of GC×GC in our study is 18 times better than that of ‘normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent. Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC) and GC×GC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results of GC×GC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second dimension chromatograms is always present.
    Additional Material: 5 Ill.
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  • 121
    ISSN: 0935-6304
    Keywords: Bornane congeners ; toxaphene compounds ; heart-cut multidimensional gas chromatography ; enantioselectivity ; chiral GC separation ; biological samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The enantiomeric ratios of the chlorinated bornanes, 2-exo, 5,5,9,9,10, 10-heptachlorobornane (B[20030]-(022)), 2-endo,3-exo,5-endo,6-exo,8, 8,10,10-octachlorobornane (B[12012]-(202), Parlar No. 26), 2-exo,3-endo,6-endo,8,9,10,10-heptachlorobornane (B[21001]-(112)), 2,2,5,5,9,9, 10,10-octachlorobornane (B[30030]-(022), Parlar No. 38), 2-endo,3-exo,5-endo6-exo,8,8,9,10,10-nonachlorobornane (B[12012]-(212), Parlar No. 50), and 2,2,5,5,8,9,9,10,10-nonachlorobornane (B[30030]-(122), Parlar No. 62) were determined in a hake liver (Merluccius merluccius) and in two whitebeaked dolphin blubber (Lagenorynchus albirostris) samples. The analysis was performed by heart-cut multidimensional gas chromatography using an electron capture detector (ECD). Ultra 2 (5%-phenyl-95%-methylsilicone) was used as stationary phase in the first column and enantioselectivity was obtained in the second column with a phase consisting of a mixture of OV-1701 and heptakis(2,3,6-O-tert- butyldimethylsilyl)-β-cyclodextrin (10 : 1). All reference standards were also tested on the enantioselective column alone. The comparison of the two systems showed that deviations of ±0.12 from the racemic enantiomer ratio can be observed for the single column due to co-eluting impurities which are present in the reference standards. In most of the heart-cut chromatograms of the biota samples about 15 peaks could be found, showing the importance of a multidimensional separation system for an interference-free quantification by ECD. In all biological samples a significant deviation from the racemic enantiomer ratio was found for B[30030]-(022) (Parlar No. 38) and for B[30030]-(122) (Parlar No. 62). This indicates that an enantioselective disposition of the congeners occurs. In addition, considerations are presented concerning the relationship between congener structure and enantiomeric disposition.
    Additional Material: 4 Ill.
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  • 122
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 69-71 
    ISSN: 0935-6304
    Keywords: liquid chromatography ; chiral separations ; chiral stationary phase ; separation of enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 123
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 3-10 
    ISSN: 0935-6304
    Keywords: Co-electroosmotic capillary electrophoresis ; high performance liquid chromatography ; phenolic lignin degradation compounds ; inorganic anions ; organic modifiers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two methods are presented for the quantitative capillary electrophoretic (CE) determination of phenolic lignin degradation compounds as well as of inorganic anions and organic acids in Kraft black liquors. Important phenolic lignin degradation compounds can be rapidly separated by co-electroosmotic CE after acidification of the liquors and subsequent extraction of the compounds with chloroform. A capillary electrophoretic separation of phenolic compounds is performed by using a phosphate/borate electrolyte system and UV detection at 214 nm. In addition, a HPLC method using a gradient with water, methanol, and acetic acid is also developed. Inorganic ions which are of importance to the pulping process can be determined by simply diluting the black liquors after sampling and subsequent analysis with a chromate electrolyte system and indirect UV detection at 185 nm. In addition, the concentration of low molecular aliphatic carboxylic acids can be determined simultaneously within the same run. By method optimization it is possible to separate the anions within one minute and, at the same time, to increase the resolution of the solutes. The electrolyte systems for the CE separations were optimized by varying the pH value and by adding organic solvents. Short separation times are obtained by adding a polycationic EOF modifier (hexadimethrine bromide) to the electrolyte which reverses the electroosmotic flow. A migration of the anionic analytes in the same direction as the electroosmotic flow is thus established.
    Additional Material: 8 Ill.
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  • 124
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 81-86 
    ISSN: 0935-6304
    Keywords: Available niacin ; capillary electrophoresis ; total niacin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Available and total niacin content in lentils and faba beans have been analyzed by capillary electrophoresis (CE), and the results compared with those obtained by high performance liquid chromatography (HPLC). Acidic and enzymatic hydrolysis have been carried out for available niacin determination, and an alkaline extraction performed for total niacin. The extracts were subsequently purified using a strong anion exchanger resin. Precise conditions for purification had to be worked out for each one of the two analytical methods (HPLC and CE). The HPLC analysis for available and total niacin was carried out in an ion-pair reverse phase column with UV detection at 261 nm. For the CE separation, the following conditions were employed: a 20 mM sodium tetraborate; 15 mM sodium dodecyl sulfate and 20% isopropyl alcohol solution as separation buffer; 30 kV and 25 or 30°C. Separation was carried out in a 70 cm effective length × 75 μm i.d. fused-silica capillary using on-column UV detection at 254 nm. The results obtained by CE for lentils and faba beans were similar to those obtained by HPLC.
    Additional Material: 2 Ill.
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  • 125
    ISSN: 0935-6304
    Keywords: supercritical fluid chromatography ; experimental design optimization ; Diesel fuel ; group-type analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An optimization procedure is presented for group-type analysis of diesel fuel by supercritical fluid chromatography using packed silica column and a mixed mobile phase. A set of five responses, four values of resolution of a performance mixture and analysis time, was modeled using a Doehlert matrix for experimental design. Optimized experimental conditions for the five responses were obtained from a response surfaces optimization, taking into account various constraints on SF6 content in mobile phase and analysis time. The predicted and experimental resolutions were in good agreement for the different optimized conditions and one of them was selected to for application to a given diesel fuel for comparison with the results obtained by SFC using pure CO2 and by HPLC. The conditions found in this study provide an alternative method for the determination of mono-, di-, and polyaromatic compounds in middle distillates.
    Additional Material: 9 Ill.
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  • 126
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    Journal of High Resolution Chromatography 21 (1998), S. 309-314 
    ISSN: 0935-6304
    Keywords: Chlorophenols ; separation ; CZE ; pH ; organic modifiers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 127
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    Journal of High Resolution Chromatography 21 (1998), S. 298-302 
    ISSN: 0935-6304
    Keywords: Toxaphene ; thermal decomposition ; stationary phases ; gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Some toxaphene congeners are thermally unstable under commonly used gas chromatographic temperature conditions. The thermal stability of the 22 commercially available congeners has been studied at four different heating rates on four stationary phases Ultra 2 (5%-diphenyl-95%-dimethylpolysiloxane), a liquid crystalline phase (N,N′-bis(p-butoxy-benzylidene)-α,α′-bis-p-toluidine), Rtx-2330 (90%-biscyanopropyl-10%-phenylcyanopropyl-polysiloxane), and heptakis-(2,3,6-O-t-butyldimethylsilyl)-β-cyclodextrin (TBDMS-CD) diluted in OV-1701-OH. A substantial degradation of the congeners Parlar 39, 42, 50, 56, 58, and 62 could be observed on the cyanopropyl polysiloxane stationary phase. Furthermore, the applied temperature program and stationary phase had an influence on the signal areas. These factors are important for a quantitative analysis.
    Additional Material: 3 Ill.
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  • 128
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    Journal of High Resolution Chromatography 21 (1998), S. 317-320 
    ISSN: 0935-6304
    Keywords: GC/MS analysis ; SIM mode ; UV stabilizers ; PET ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 129
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    Journal of High Resolution Chromatography 21 (1998), S. 323-331 
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; chiral separations ; chiral crown ethers ; 18-crown-6-tetracarboxylic acid ; synthesis ; applications ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An overview is presented of the applicability of the crown ether 18-crown-6-tetracarboxylic acid (18C6H4) as buffer additive in capillary electrophoresis (CE) for the separation of enantiomers. The chiral selector 18C6H4 is particularly useful for the separation of racemates having a primary amino function. Unfortunately, the crown ether is no longer commercially available. The synthesis and spectroscopic characterization are therefore described in detail. Moreover, a method is presented for the regeneration of the crown ether after CE application. Some new enantiomeric separations of amino acids i.e. NORLEU, ARG, GLU, m-TYR, and o-TYR are listed and the influence of the pH and temperature of the separation buffer is discussed. An intermediate in the synthetic pathway, namely 18-crown-6-tetracarboxamide, did not exhibit any enantioselectivity in CE.
    Additional Material: 6 Ill.
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  • 130
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    Journal of High Resolution Chromatography 21 (1998), S. 363-367 
    ISSN: 0935-6304
    Keywords: high temperature gas chromatography ; triacylglycerol ; lipids ; Jatropha multifida ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 131
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    Journal of High Resolution Chromatography 21 (1998), S. 303-307 
    ISSN: 0935-6304
    Keywords: gas chromatography ; modified silica gel ; gaseous standard mixtures ; FID calibration ; carbon monoxide and carbon dioxide ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quartz rods coated with a thin layer of chemically modified silica gel have been used for the generation of a two-component gaseous standard mixture containing carbon monoxide and carbon dioxide. A new method based on thermal decomposition of immobilized compounds chemically bonded to the surface of silica gel has been used in the generation process. The oxalic acid moiety bonded to the glycydoxypropylsilylated surface of silica gel underwent decarbonylation and decarboxylation at 300°C, yielding carbon monoxide and carbon dioxide. On-line connection of a thermal desorber with the GC/FID enabled calibration of the detector following the process of methanization of CO and CO2. The following amounts of CO and CO2 were generated per unit length of the rod: 15.1 × 10-8 Mol cm-1 (RSD = 5.71%) for CO and 34.2 × 10-8 Mol cm-1(RSD = 5.16%) for CO2.
    Additional Material: 4 Ill.
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  • 132
    ISSN: 0935-6304
    Keywords: Large-volume on-column injection ; gas chromatography ; infrared spectrometry ; microcontaminants ; solid-phase extraction ; open-split interface ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A large-volume on-column GC-cryotrapping-IR system was developed for injections of up to 100 μl of organic extracts. Considerable reduction of the solvent-and-water background and enhanced analyte detectability was achieved by using an open-split interface between the GC column and the IR detector and improving the leak-tightness of the system. The system was combined with solid-phase extraction to yield on-line SPE-GC-IR. With this set-up, sample volumes of only 20 ml sufficed to detect, and identify, microcontaminants in tap and surface water at the 0.1-1 μg/L level. Detection limits were on the order of 15 ng/L for tap water when using appropriate functional-group chromatograms. Or, in other words, SPE-GC-IR is a suitable technique for the screening of environmental water samples for functional groups, i.e. classes of compounds, of interest.
    Additional Material: 5 Ill.
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  • 133
    ISSN: 0935-6304
    Keywords: gas chromatography ; sorptive preconcentration ; air sampling ; VOCs ; nitro-PAH's ; PAHs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper is concerned with the determination of volatile and semi-volatile organic components in air and gaseous (headspace) samples, focusing primarily on polar analytes. Samples were analyzed by preconcentration on different (ad)sorbents followed by thermal desorption and analysis by capillary gas chromatography. The performance of a cartridge filled with 100% polydimethylsiloxane (PDMS) particles was compared to that of adsorbents like Tenax TA and Carbotrap 300. Though the PDMS phase is non-polar it showed adequate retention for both polar and non-polar components. The blank runs of the PDMS trap were significantly better than those of most adsorbents and did not deteriorate, as was the case with all the conventional adsorbents investigated. With respect to trapping efficiencies, the PDMS phase performed better for most of the analytes under investigation compared to the adsorbents. For a range of analytes including triethylamine, butanone, diacetyl, nicotine, and acetic acid the PDMS phase performed exceptionally well whereas all adsorbents showed unsatisfactory performance. The packed PDMS traps were employed for the determination of organic acids, PAH's and nitro-PAH's in air and for the analysis of the headspace of cacao and hop.
    Additional Material: 9 Ill.
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  • 134
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    Journal of High Resolution Chromatography 21 (1998), S. 347-354 
    ISSN: 0935-6304
    Keywords: Fragrances ; chirality evaluation ; semi-automated multidimensional gas chromatography ; infrared spectrometry ; mass spectrometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The use of a semi-automated, multidimensional gas chromatography (MDGC) Fourier transform infrared (FT-IR) mass spectrometry (MS) system in the determination of components causing contact dermatitis has been investigated. Fragrances are widely used in cosmetic and household products and are the leading cause of contact dermatitis. Such products contain numerous components such as emulsifiers, thickeners, solubilizers, pigments, antioxidants, and many other compounds, which can make it difficult to isolate the compound of interest. MDGC has the capability for component analysis in such complex matrices. A semi-automated MDGC system, which consists of a commercial instrument modified in our laboratory to include two computer controlled valves and a single trap which is manually controlled was evaluated for analysis of irritants in a total of thirteen soaps. Using heartcutting techniques, components causing dermatitis were identified in eight of the thirteen soaps by examining both the infrared and mass spectra obtained and matching them with computer spectral libraries. Results from these analyses show that a baby soap and three other mild soaps were free of irritants. Irritants were identified in the remaining eight soaps. In addition, to demonstrate the versatility of the semi-automated system, the enantiomeric composition of a chiral irritant in two soaps also was determined.
    Additional Material: 8 Ill.
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  • 135
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    Journal of High Resolution Chromatography 21 (1998), S. 368-370 
    ISSN: 0935-6304
    Keywords: Solid-phase microextraction ; headspace analysis ; gas chromatography ; mass spectrometry ; volatile analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 136
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    Journal of High Resolution Chromatography 21 (1998), S. 575-576 
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography (CEC) ; chiral separations ; Vancomycin stationary phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 137
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    Journal of High Resolution Chromatography 21 (1998), S. 577-581 
    ISSN: 0935-6304
    Keywords: Volatiles ; Bromeliaceae ; Bromelia plumieri ; glycosidically bound volatiles ; aroma precursors ; glucoconjugates ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 138
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    Journal of High Resolution Chromatography 21 (1998), S. 649-652 
    ISSN: 0935-6304
    Keywords: capillary gas chromatography ; NPD ; nicotine ; pharmaceutical analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The delivery of drugs through human skin using transdermal drug delivery (TDD) systems has become an established technology. A popular drug with that dosage form is nicotine for smoking cessation. A stability indicating method for the analysis of nicotine TDDs using gas chromatography (GC) with post-column effluent splitting to a flame ionization detector (FID) and a nitrogen-phosphorus detector (NPD) is described. FID detection gave reliable results with low day-to-day variability. The detector is relatively simple to operate. NPD detection offered enhanced sensitivity and specificity. The combination of both detectors resulted in a rugged method for content analysis with high sensitivity for detection of degradation products at low concentration levels. Despite a relatively simple sample preparation procedure no matrix interferences were observed.
    Additional Material: 3 Ill.
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  • 139
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    Journal of High Resolution Chromatography 21 (1998), S. 665-666 
    ISSN: 0935-6304
    Keywords: SPME; GC/MS ; Hg2+ and CH3Hg+ urine samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 140
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    Journal of High Resolution Chromatography 21 (1998), S. 653-657 
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; mass spectrometry ; CE-MS ; amphetamines ; Ecstasy ; biological fluids ; urine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Capillary electrophoresis (CE) was interfaced with a quadrupole mass spectrometer, using pneumatically-assisted electrospray ionization (ESI) in order to analyze Ecstasy and derivatives in urine. The influence of the sheath liquid composition, including the type and the percentage of the organic solvent, as well as the nature of the conductive acid modifier, were examined in order to find optimal coupling conditions. A fractional factorial design was also used to optimize the electrospray experimental parameters, such as the nebulizing gas pressure, the electrospray voltage, the drying gas flow rate, the drying gas temperature, the skimmer voltage, and the sheath liquid flow rate. The separation conditions were optimized in terms of temperature, electrolyte concentration, percentage of organic modifier, as well as capillary type. Finally, the optimal CE-ESI-MS conditions were applied to the analysis of Ecstasy and other related amphetamines in urine samples, following a liquid-liquid extraction procedure.
    Additional Material: 7 Ill.
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  • 141
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    Journal of High Resolution Chromatography 21 (1998), S. 671-673 
    ISSN: 0935-6304
    Keywords: gas chromatography ; monosaccharides ; pentafluorobenzylhydroxylamine ; electron capture detector ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 142
    ISSN: 0935-6304
    Keywords: Fluoroquinolone ; ASTED ; HPLC fluorescence ; sarafloxacin ; flumequine ; oxolinic acid ; chicken liver ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A recently introduced programmable fluorescence detector was compared with a single wavelength fluorescence detector for quantification of fluoroquinolone (FQ) antibacterial agents, which have widely varying spectral characteristics. The two detectors were connected in parallel to an HPLC system to test their performance characteristics. With single wavelength detection, two FQs, flumequine and oxolinic acid could be detected at an emission wavelength of 368 nm in a single chromatogram while a third FQ, sarafloxacin, was not observed at that wavelength. Similarly, when the detector was optimized for sarafloxacin emission at 440 nm, the other two compounds were undetected. In contrast, all three FQs were quantified at their individual maxima in a single run using the programmable fluorescence detection. The applicability of an HPLC - programmable fluorescence detector, in combination with on-line microdialysis, also was evaluated using chicken liver fortified at low ppb levels with the three FQs. After on-line microdialysis sample clean up, the resultant HPLC chromatograms were free of background interference enabling the programmable detector to optimize the quantitation of the three analytes in a single run. The limit of quantification (LOQ) determined for each FQ was 1.0 ppb and the limit of detection (LOD) was 0.2 ppb, an order lower in magnitude than was obtainable with single wavelength detection.
    Additional Material: 3 Ill.
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  • 143
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    Journal of High Resolution Chromatography 21 (1998), S. 267-281 
    ISSN: 0935-6304
    Keywords: Chemically bonded phases, CBPs ; liquid chromatography, HPLC ; preparation; surface characterization ; column evaluation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In order to increase chromatographic selectivity and to extend the analytical capability of reversed phase liquid chromatography (RP HPLC) many investigators have concentrated on the preparation of silica based column packings with chemically bonded phases (CBP). These phases have also been successfully used in sample preparation techniques, mainly in solid phase extraction (SPE). Although alkyl bonded phases (e.g., C2, C8, and C18) are the most widely used packings in RP HPLC and SPE, various specific applications require CBPs with polar functional groups (e.g., -NH2, -NO2, -CN, and/or -OH). The solution of problems with separation of complicated chiral compounds was attempted by applying stationary phases with chiral selectors (e.g., cyclodextrins, Pirkle phases, crown ethers, etc.). On the other hand, packings with pseudo-membrane or liquid crystal properties have been utilized for the separation of various substances of natural origin. Porous silica is commonly used as a support in the preparation of CBPs. Its physico-chemical characteristics, such as: type and structure of siliceous matrix, porosity, type and concentration of silanol groups, as well as surface purity, strongly influence the density and structure of chemically bonded phases. Recognition of these properties is helpful in optimizing separation processes based on RP HPLC elution and/or extraction of substances with polar character.
    Additional Material: 12 Ill.
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  • 144
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    Journal of High Resolution Chromatography 21 (1998), S. 287-290 
    ISSN: 0935-6304
    Keywords: DNA ; capillary electrophoresis ; sample injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Silver-coated capillaries were used for direct sample injection in multiplexed capillary electrophoresis. The absence of an additional electrode simplifies mechanical alignment, reduces contamination, and decreases the amount of sample needed. Capillaries were coated by a silver paint which is a suspension of silver particles in an organic solvent. To provide electrical contact, the upper part of the capillary and a platinum wire were wound together by a copper wire. Electrical resistance from the platinum wire to the tip of the capillary was small enough (7 ω to 50 ω) to inject large amounts of DNA samples. Electrokinetic injection from eight separate sample vials to eight capillaries was demonstrated for DNA sequencing by multiplexed capillary electrophoresis. Signal-to-noise ratio and resolution were good enough to call up to 350 base pairs.
    Additional Material: 3 Ill.
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  • 145
    ISSN: 0935-6304
    Keywords: capillary gas chromatography ; microplasma mass spectrometry ; radio frequency plasma ; element-selective detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Capillary gas chromatography was performed with mass spectrometric detection using a novel microplasma ion source for operation in an element-selective mode. The ion source was a 350 kHz radio frequency helium plasma, which was sustained inside the 4 cm end of a 0.32 mm i.d. fused silica capillary column, and located inside the high vacuum chamber of the quadrupole mass spectrometer. Due to the low volume of the ion source, a stable low pressure discharge was produced utilizing only the 2.25 mL min-1 of GC carrier gas (helium) for plasma support. Small amounts of oxygen (0.1-0.2% v/v) were added to the plasma gas in order to prevent carbon deposits and to enhance signal-to-noise ratios. Chlorine and bromine were selectively detected at the 5-20 pg s-1 level (S/N = 2), and both produced a response that was linear within 3 orders of magnitude.
    Additional Material: 3 Ill.
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  • 146
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    Journal of High Resolution Chromatography 21 (1998), S. 315-316 
    ISSN: 0935-6304
    Keywords: Tertiary amine ; ruthenium ; chemiluminescence ; photochemical oxidation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 147
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    Journal of High Resolution Chromatography 21 (1998), S. 355-362 
    ISSN: 0935-6304
    Keywords: Large volume injection ; solvent evaporation ; flooded zone ; solvent trapping ; on-column injection ; water analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Using a specially treated glass capillary, evaporation of the solvent during large volume injection into a precolumn was visually investigated in order to better understand the solvent trapping process. Using an early vapor exit, the process differs from the classical description of solvent trapping. First, there is a substantial pressure drop over the solvent-coated (“flooded”) precolumn, causing evaporation to take place not only at the rear edge, but also within the flooded zone or at its front end (which may result in almost complete loss of volatile solutes). Secondly, the evaporation rate increases as the liquid enters deeper into the precolumn, eventually turning partially concurrent evaporation into a fully concurrent evaporation with massive loss of volatiles. Thirdly, the capacity of the precolumn to retain liquid is substantially higher than observed in systems without early vapor exit
    Additional Material: 10 Ill.
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  • 148
    ISSN: 0935-6304
    Keywords: Headspace solid-phase microextraction (HS/SPME) ; capillary gas chromatography ; volatile wine aroma compounds ; aromatic pattern ; chemometric classification ; HS/SPME standard addition method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Headspace solid-phase microextraction (HS/SPME) was studied and optimized for the capillary gas chromatographic (CGC) analysis of wine aroma compounds. The results were compared with those obtained using the direct sampling mode (DI/SPME) and using liquid/liquid extraction with Kaltron. The aromatic patterns obtained by HS/SPME-CGC were applied to the chemometric classification of wine varieties. The HS/SPME-CGC standard additional method is an appropriate technique for the quantitative analysis of volatile wine aroma compounds.
    Additional Material: 8 Ill.
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  • 149
    ISSN: 0935-6304
    Keywords: Oil ; oil spill ; GC/MS ; GC/FID ; carbon isotope ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---During January and February 1996, a significant number of tarball/patty incidents occurred along the coasts of Vancouver Island, Washington, Oregon, and California. Samples of the tarballs were collected from the affected beaches and analyzed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/flame ionization detector (GC/FID) using a tiered analytical approach developed for determining the origin of oils. Selected samples were further analyzed using a carbon isotopic technique. Also, the relative abundances of a large number of “source-specific marker” compounds, in particular alkylated series of polycyclic aromatic hydrocarbons within the same alkylation isomeric groups, were compared. Results of the analysis revealed that (1) California/Oregon samples were chemically similar and consistent with the same source. They were identified to be bunker type fuel; (2) The tarball samples collected from British Columbia and Ocean Shores, Washington were chemically similar and consistent with the same source (also bunker type fuel). They were found to be similar to but may have a source different than the California/Oregon samples; (3) The source of the tarball/patty samples was neither Alaska North Slope oil nor California Monterrey Miocene oil; (4) The spilled oil samples have been highly weathered since release, and the California samples were more heavily weathered than the British Columbia samples.
    Additional Material: 7 Ill.
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  • 150
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    Journal of High Resolution Chromatography 21 (1998), S. 407-410 
    ISSN: 0935-6304
    Keywords: Capillary GLC ; nitrous oxide as carrier gas ; carrier gas correlation of retention factors ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On use of nitrous oxide as carrier gas the retention factors of the chromatographed compounds decrease linearly with increasing average column pressure. Other retention characteristics (relative retention, retention index) change linearly. This effect was demonstrated by using a capillary column coated with nonpolar polydimethylsiloxane phase SE-30. As shown for capillary GLC the linear correlation is valid for the same column:ki(G1,P1) = A ki(G2, P2) + B, where ki(G1, P1) and ki(G2,P2) are the retention factors of compound i at average column pressures P1 and P2 when using carrier gases G1 and G2, respectively; A and B are coefficients.
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  • 151
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    Journal of High Resolution Chromatography 21 (1998), S. 414-416 
    ISSN: 0935-6304
    Keywords: chiral separation ; HPLC ; diols ; borate complexation ; cyclodextrin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 152
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    Journal of High Resolution Chromatography 21 (1998), S. 421-423 
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; chiral separation ; cyclodextrins ; bencynonate ; econazole ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 153
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    Journal of High Resolution Chromatography 21 (1998), S. 440-444 
    ISSN: 0935-6304
    Keywords: enantiomeric separation ; β-amine alcohols ; capillary electrophoresis ; DM-β-CD ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Enantiomeric separations of several β-amino alcohol drugs, i.e., phenylephrine, epinephrine, norepinephrine, synephrine, and chlorprenaline were performed by capillary electrophoresis using DM-β-CD as a chiral selector. Five test solutes were baseline resolved in six minutes. The effects of DM-β-CD concentration, pH value, ionic strength of the buffer, and the type of β-CDs on resolution were investigated. The results indicated that DM-β-CD is suitable for enantiomeric separation of β-amino alcohols containing a phenyl group on the chiral atom. Enantiorecognition mechanisms for test solutes are also discussed.
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  • 154
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    Journal of High Resolution Chromatography 21 (1998), S. 457-463 
    ISSN: 0935-6304
    Keywords: Supercritical Fluid Extraction (SFE) ; ultrasonication extraction ; gas chromatography ; derivatization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Supercritical fluid extraction (SFE) of alkyl alkylphosphonofluoridates and dialkyl alkylphosphonates from painted plates was investigated. It was found that SFE recoveries compared favorably with conventional solvent sonication results. Stability studies of the samples were carried out over a period of two months. This investigation showed that the concentration of phosphonofluoridates decreased over a long period.
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  • 155
    ISSN: 0935-6304
    Keywords: Adsorption/thermal desorption sampling instrument ; capillary gas chromatography ; electrolytic conductivity detector ; photoionization detector ; environmental air monitoring ; hazardous air pollutants ; volatile organic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 156
    ISSN: 0935-6304
    Keywords: Scent glands ; defense substances ; n-alkanes ; furanones ; 2-alkenals ; 2-alkenyl acetates ; 2-decenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 157
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    Journal of High Resolution Chromatography 21 (1998), S. 491-497 
    ISSN: 0935-6304
    Keywords: Fast GC ; narrow-bore columns ; trace analysis ; splitless injection ; on-column injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The use of hot splitless, cold splitless, and on-column injections for trace analysis in narrow-bore capillary GC is evaluated. Despite the low flow rates for the columns used, the required splitless times for splitless injections can be surprisingly short if liners with a small inside diameter are used. On-column injection can be applied by using an appropriate normal-bore precolumn coupled to the narrow-bore analytical column using a specially designed low dead volume column connector. The effects of the experimental conditions such as sample volume, injection temperature, and initial oven temperature on peak focusing and the discrimination and degradation behavior of the analytes are discussed. The possibilities to obtain sensitive and fast separations are illustrated by various applications.
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  • 158
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    Journal of High Resolution Chromatography 21 (1998), S. 481-490 
    ISSN: 0935-6304
    Keywords: solid-phase extraction ; estrogens ; urine ; solvation parameter model ; system maps ; gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general model is presented for the prediction of experimental conditions for the isolation of organic compounds from aqueous solution by solid-phase extraction. The solvation parameter model is used to predict the variation of retention as a function of solvent composition from characteristic solute descriptors and combined with a frontal analysis model to adjust the predicted breakthrough volumes to account for the influence of the small number of theoretical plates characteristic of sorbent cartridges. System maps are used to determine breakthrough volumes for sample processing, the composition and volume of wash solvents for matrix simplification, and the composition and volume of eluting solvents. System maps are provided for an octadecylsiloxane-bonded silica sorbent with methanol and acetonitrile as cosolvents with water. These maps are used to calculate the experimental conditions for the isolation of estrogens from urine and the model validated by experimental verification of the model predictions. The proposed approach provides a simple theoretical framework for computer-aided method development in solid-phase extraction.
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  • 159
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    Journal of High Resolution Chromatography 21 (1998), S. 505-508 
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; inorganic ions ; polyethyleneimine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A capillary zone electrophoresis (CZE) method for the simultaneous assay of bromide, iodide, nitrite, nitrate, and thiocyanate using direct UV detection is reported. The method is based on the separation of anions in a capillary coated with a cationic polymer, polyethyleneimine (PEI). The minimum detection limits, reproducibility of peak areas, and migration times were determined at the optimal condition. The method was applied to the analysis of tap water and human urine. The changes in separation selectivity of the anions resulting from addition of the cationic polymer to the buffer were investigated.
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  • 160
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    Journal of High Resolution Chromatography 21 (1998), S. 523-526 
    ISSN: 0935-6304
    Keywords: High-performance liquid chromatography ; gardenia constituent separation ; genipin gentiobioside ; geniposide ; crocin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 161
    ISSN: 0935-6304
    Keywords: Cold on-column injector ; high temperature high resolution gas chromatography ; rotenoids ; PS-090 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short glass capillary column coated with PS-090 (20% phenyl-80% methylpolysiloxane, of 10 m × 0.30 mm i.d.; with 0.1 μm film thickness) was used to analyze samples from Tephrosia candida; eighteen rotenoids were separated and identified without derivatization by HT-HRGC and HT-HRGC-MS. The mass spectra show the typical fragmentation pattern for rotenoids, with the base peaks either at M+, or originating from RDA (Retro Diels-Alder) rearrangements. HT-HRGC and HT-HRGC-MS were shown to be extremely valuable and neglected techniques for structural studies as well as the routine analysis of rotenoids in crude extracts. Possible applications to other classes of aromatic natural products, e.g. flavonoids, are envisaged.
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  • 162
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    Journal of High Resolution Chromatography 21 (1998), S. 540-544 
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; thermionic detector ; nitrogen-selective detection ; eluent-jet interface ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The on-line coupling of capillary electrophoresis (CE) with a thermionic detector (TID) originally developed for gas chromatography (GC) is reported for the first time. An eluent-jet interface previously used to combine micro-liquid chromatography and mass spectrometry can now be used to couple CE and TID. Preliminary results demonstrate the possibility of performing direct nitrogen-selective detection, even for less volatile compounds. Detection limits of 4-12 pg N/s were obtained for the four tested compounds piperidine, dimethylformamide, tetra-n-butylammonium hydroxide, and nicotinic acid. Optimization of both the TID and the eluent-jet interface can be performed independently; optimum TID parameters agree rather closely with the detector specifications under GC conditions. The nitrogen-selective TID proved to be linear over more than three orders of magnitude with acceptable repeatability. The on-line coupling of CE and TID may well become an interesting approach for the rapid and direct analysis of ionic and high-molecular-mass N-containing compounds.
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  • 163
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    Journal of High Resolution Chromatography 21 (1998), S. 545-548 
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography (CEC) ; fish oil ; triglycerides ; free fatty acids (FFAs) ; fatty acid methyl esters (FAMEs) ; fatty acid phenacyl esters (FAPEs) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Capillary ElectroChromatography (CEC) on a fused silica capillary column (40 cm L × 100 μm i.d.) packed with 3 μm octadecylsilica (ODS) was evaluated for the analysis of the triglycerides and their fatty acids in fish oils, and more especially in the oil of Moroccan Sardinia pilchardus. The very high complexity of the lipids in fish oil is well illustrated by CEC with a nonaqueous mobile phase consisting of acetonitrile/isopropanol/n-hexane in the ratio 57/38/5 to which 50 mM ammonium acetate has been added. In order to unravel the complexity, the oil was hydrolyzed and the free fatty acids (FFAs), the methyl esters (FAMEs), and the phenacyl esters (FAPEs) were analyzed by CEC on the same column used for the analysis of the triglycerides. Isocratic elution was achieved with the mobile phase acetonitrile/50 mM MES pH 6 in ratio 9/1. The migration characteristics of FFAs, FAMEs, and FAPEs are compared. The analysis of FAPE derivatives has the advantage that quantification applying UV detection is possible and moreover that the number of double bonds in the fatty acid chains can be elucidated by measuring the UV abundance ratio 240/210 nm.
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  • 164
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    Journal of High Resolution Chromatography 21 (1998), S. 569-573 
    ISSN: 0935-6304
    Keywords: Chinese herbal preparation ; Shao-yao-tang ; pharmaceutical analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A high-performance liquid chromatographic method for the separation of twenty one constituents of Shao-yao-tang including six flavonoids, six alkaloids, three anthraquinones, three carboxylic acids, one monoterpene, one saponin, and one aldehyde was developed. Detection at 275 nm with a linear gradient elution system consisting of tetrabutylammonium bromide (TBA) and acetic acid solution was found to be suitable for determination of nineteen marker substances in an unpretreated Shao-yao-tang extract within 75 min. This method can also be used to analyze 11-14 components in a number of Chinese herbal preparations such as San-huang-hsieh-hsin-tang, Ching-chieh-lien-chiao-tang, San-tsung-kuei-chien-tang, Chai-hu-ching-kan-tang, and Ching-yin-li-ke-tang.
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  • 165
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    International Journal of Quantum Chemistry 62 (1997), S. 265-272 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Numerical experiments with a nonlinear (λχ4) oscillator which has its harmonic frequency changing randomly with time reveal certain interesting features of its dynamics of quantum evolution. When λ = 0, the level populations are seen to oscillate. But, as the nonlinear coupling is switched on (λ 〉 0), a threshold is reached at λ = λc when the evolution is seen to be characterized by an abrupt transition dominantly to the highest available state of the unperturbed (initial) oscillator. It is shown that this transition probability is maximized at a particular value of λ. The time threshold for this transition decreases with increasing nonlinear coupling strength. The numerically obtained structures of the underlying quantum-phase spaces of the linear and nonlinear random oscillators are examined. Possible use of these results in a problem of chemical origin is explored. © 1997 John Wiley & Sons, Inc.
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  • 166
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    International Journal of Quantum Chemistry 62 (1997), S. 279-289 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Testosterone (17β-hydroxy-4-androsten-3-one) was studied by the semiempirical AM1 and PM3 and ab initio STO-3G*, 3-21G*, and 6-31G* methods. The goals were to compare those methods and to know the electronic structure of the hormone. Full geometry optimization was performed, and two crystal conformers (T1 and T2), and experimental dipole moment in solution were used for comparison. One conformer with a dipole moment similar to the solvated conditions was generated. Total energy, entalphies, dipole moments, charges, electrostatic potentials, and highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbital (LUMO) were calculated. Root-mean-square (RMS) index of the theoretical molecules against T1 and T2 showed best results with the 3-21G* and 6-31G* methods, while AM1 gave better energies than PM3. Dipole moments were directed toward the OH group and the botton face of the A ring. The frontier orbitals were located along the C4-C5 π bond, particularly the LUMO was split between C4 and C5, predicting the action of enzymes at C5 yielding to 5α and 5β-reduced androgens. Electrostatic potentials might be also of biological importance since they are coincidental with the dipole-moment orientation. Finally, it is interesting that the solvatedlike conformer, its properties, and the OH group laid between the same group of T1 and T2 and with a total energy between the crystals and the gas phase or in vacuo conditions. This results might also explain the biology of testosterone and use them to model the hormone-receptor interaction. © 1997 John Wiley & Sons, Inc.
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  • 167
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    International Journal of Quantum Chemistry 62 (1997), S. 303-314 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: He I photoelectron (PE) spectra of four carboxylic acids and five esters are measured. Semiempirical and ab initio quantum chemical calculations are used for the interpretation of the spectra. The complex approach which uses empirically established relationships (the dependence of valence electron ionization energies on proton affinities in the gas phase, on the core level ionization energies, and on the structure) was developed. © 1997 John Wiley & Sons, Inc.
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  • 168
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    International Journal of Quantum Chemistry 62 (1997), S. 323-328 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simple molecular orbital calculations are employed in searching electronic parameters which may characterize the chemical carcinogens. Using frontier orbitals, the carcinogen-DNA bond formation is described as an electron transfer from the highest occupied molecular orbital (HOMO) of DNA to the lowest unoccupied molecular orbital (LUMO) of the carcinogen. Analysis of the DNA bases units shows that the electron donation occurs preferentially at the guanine site. The calculated low LUMO energy of several carcinogens indicate correctly the electrophilic character of these compounds. The difference between the carcinogen and the ultimate carcinogen is analyzed. Epoxides, free radicals, alkylating agents, and other metabolite forms are studied. A reasonable correlation is found between the LUMO energy and the carcinogenic function. © 1997 John Wiley & Sons, Inc.
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  • 169
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    International Journal of Quantum Chemistry 63 (1997), S. 1123-1131 
    ISSN: 0020-7608
    Keywords: MD simulations ; liquid surface ; formamide ; molecular orientation ; molecular surface density ; Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations of liquid formamide(HCONH2) were carried out using the GROMOS software. The formamide molecule is represented by all of its atoms with all internal degrees of freedom. In contrast to other simulations dealing with bulk properties, this study focuses on the interface liquid-vacuum for the first time. We show that the molecular plane is tilted out of the surface, exposing the HCO group to the vacuum.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1123-1131, 1997
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  • 170
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    International Journal of Quantum Chemistry 63 (1997), S. 1065-1078 
    ISSN: 0020-7608
    Keywords: very precise eigenvalues ; very accurate grid method ; general solution for Schrödinger equations ; rapidly convergent treatment for helium eigenvalues ; superconvergence ; optimization of grids ; treatment of continuum ; Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An extension to the theory of Schrödinger equations has been made which enables the derivation of eigenvalues from a consideration of a very small part of geometric space. The concomitant unwanted continuum effects have been removed. The theory enables very convergent or “superconvergent” calculations. In the case of the helium ground state, E=-2.90372437703411987 Eh was obtained from 251 terms. The result is comparable to that from the largest variation calculations so far carried out reinforced by extrapolation techniques. The theory is extensible to atoms and molecules irrespectively of the number of electrons or nuclear centers. In these cases, the advantage of “superconvergent” calculations will be more pronounced than in the case of helium.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1065-1078, 1997
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  • 171
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    International Journal of Quantum Chemistry 62 (1997), S. 1-11 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Roothaan-Hartree-Fock (RHF) calculations are carried out for the ground states of the atoms from helium to xenon using a minimal basis set of Slater-type functions whose principal quantum numbers are allowed to take variationally optimal noninteger values. The resulting energies are substantially superior to those obtained previously under the usual restriction that principal quantum numbers be positive integers. The energy lowering relative to the single-zeta wave functions of Clementi and co-workers ranges from 0.0066 Eh in He to 11.2 Eh in Xe. Our results are superior to those obtained by Höjer using a minimal basis set of unconventional binomially screened basis functions. Noninteger principal quantum numbers benefit d-orbitals the most; physically realistic negative d-orbital energies are obtained in all cases including those transition-metal atoms for which a conventional single-zeta STF basis leads to positive d-orbital energies. © 1997 John Wiley & Sons, Inc.
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  • 172
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    International Journal of Quantum Chemistry 62 (1997), S. 23-27 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An ab initio study on the reaction of the ground state (3D) and the excited state (1D) of Sc+ with methane was performed. Reaction channels on the singlet and triplet potential surface (PES) and the reaction mechanism are examined and discussed. Three regions of the potential surface was studied: the molecular complex, the C(SINGLE BOND)H insertion products, and the transition states for the reaction. Comparisons between singlet and triplet PESs show that the excited state (1D) of Sc+ has more reactivity with methane than does the ground state (3D) due to the spin quantum number conservation with the more stable insertion intermediate. © 1997 John Wiley & Sons, Inc.
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  • 173
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    International Journal of Quantum Chemistry 62 (1997), S. 67-76 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The importance of the hybridization displacement charge (HDC) in describing molecular electrostatic potential (MEP) maps was demonstrated by studying six molecules; pyrazine N-oxide, para-nitropyridine, 5-nitropyrimidine, 3-nitropyridazine, N2, and N2O. It is shown that continuously distributed HDC-corrected Löwdin charges reproduce the MEP features of these molecules, most of which have competing electrophilic sites, in agreement with ab initio results. Further, it is found that for homonuclear diatomic molecules MEP minima can be located properly using HDC-corrected Löwdin (or HDC-corrected Mulliken) continuously distributed charges, but these features cannot be obtained using the conventional Löwdin (or Mulliken) charges. It was shown that the order of molecular electric field (MEF) values near the different electrophilic sites becomes changed when one moves away from the molecules. Thus, pyridine-type nitrogen atoms are the preferred binding sites close to the molecules, while at large distances, effects of oxygen atoms of the NO groups become dominant. © 1997 John Wiley & Sons, Inc.
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  • 174
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    International Journal of Quantum Chemistry 62 (1997), S. 115-124 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some types of atomic vibrations in a chain of the DNA type constructed of G-C pairs were studied. These are the atomic vibrations of the lateral groups of guanine and N(3)H(1)H(2) of cytosine connected by the hydrogen bond h-b-1 and the vibrations of the centers of masses of bases in the direction parallel to bonds h-b-i, i = 1-3. The vibrations mix partially due to the dependence of the energy of the bond h-b-1 on its length and split into two bands because of the interaction between neighboring base pairs. It was shown that the excitation of the bond h-b-1 results in the splitting off of the two local vibrations and in a small deformation of the chain in the vicinity of the pair with the localized hydrogen bond. The law of the dispersion of band vibrations, values of the split-off frequencies, and degree of poly(dG)-poly(dC) chain deformation were determined. © 1997 John Wiley & Sons, Inc.
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  • 175
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    International Journal of Quantum Chemistry 62 (1997), S. 55-65 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We compare geometry configurations, vibrational properties, and electronic structures of (HF)2 in a free state and inside argon atom shells Arn. For the first stage, molecular dynamics calculations for the (HF)2 · Ar62 heterocluster are performed with the help of model potentials HF(SINGLE BOND)HF, Ar(SINGLE BOND)Ar, and Ar(SINGLE BOND)HF. Then, ab initio quantum chemistry analysis is carried out for the smaller systems (HF)2 · Ar15 and (HF)2 · Ar6 when keeping the argon atoms closest to the trapped dimer. We conclude that the hydrogen-bonded complex (HF)2 gains some extra stability inside the argon shells, originating primarily from a decrease of intermolecular distance RFF. Electronic structure calculations are in accord with the changes in dynamical properties, namely, a noticeable increase in the vibrational frequency assigned to the F(SINGLE BOND)F stretching mode (+25 cm-1) and decrease in rms deviations for the corresponding coordinate δFF. In addition to these changes, the argon atoms of the nearest solvent shell donate a small fraction of electron charge which is spent for an increase of population of the antibonding orbital σ*Hf(SINGLE BOND)Ff of the free monomer unit and shift orbital energies primarily of the lone-pair fluorine species. These shifts are greater than the changes due to geometry alterations and the possible inaccuracies of the calculation scheme. © 1997 John Wiley & Sons, Inc.
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  • 176
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    International Journal of Quantum Chemistry 62 (1997), S. 245-259 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient expansion method for the evaluation of VB matrix elements is introduced. The overlaps of VB wave functions of N electrons can be treated as algebrants, i.e., generalized determinants, of N × N matrices. An algebrant can be expanded with subalgebrants of lower orders in a successive way. By choosing Rumer spin bases and appropriately arranging the expansion, it is found that the number of unique subalgebrants involved in the expansion increases in a quite moderate way with N. In contrast to the traditional symmetric group approach, which explicitly utilizes all N! representation matrices, the new strategy incorporates the group theoretical factors in a simple way in the successive expansion. As only the unique subalgebrants are further expanded, the computational effort required by the new strategy scales in a very acceptable manner with the increasing number of electrons. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 245-259, 1997
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  • 177
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    International Journal of Quantum Chemistry 62 (1997), S. 261-264 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Characters of irreducible representations (irreps) of the symmetric group corresponding to the two-row Young diagrams, i.e., describing transformation properties of N-electron eigenfunctions of the total spin operators, have been expressed as explicit functions of the number of electrons N and of the total spin quantum number S. The formulas are useful in various areas of theory of many-electron systems, particularly in designing algorithms for evaluation of spectral density moments. © 1997 John Wiley & Sons, Inc.
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  • 178
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    International Journal of Quantum Chemistry 62 (1997), S. 291-296 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometries and S-H, S-S, and S-C bond dissociation energies for hydrogen sulfide, hydrogen disulfide, methanethiol, dimethyl disulfide, and dimethyl disulfide were calculated with both ab initio (ROHF and MP2), hybrid (BHandH, BHandHLYP, Becke3LYP and Becke3P86), and nonlocal (BLYP and BP86) density functional theory (DFT) methods. In all studies the 6-31 + G(d) basis set is used. The computed results are compared to the experimentally obtained values, targeting the selection of a suitable ab initio or DFT method for the study of these systems. © 1997 John Wiley & Sons, Inc.
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  • 179
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    International Journal of Quantum Chemistry 62 (1997), S. 297-302 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism and kinetics for the decomposition of β-hydroxypropaldehyde, primary and secondary β-hydroxyketones, were studied by using ab initio RHF/6-31G and RHF/6-31G* methods. The activation barriers of these reactions were refined to be 39.57, 40.10, and 36.80 kcal mol-1 at the MP2/ /RHF/6-31G* level, respectively. The calculated results show that each decomposition is a concerted process with hydrogen transferring and bond breaking via a six-membered cyclic transition state. The thermal rate constants of the decomposition of primary and secondary β-hydroxyketones were obtained by calculating microcanonical probability fluxes through each transition state. It is theoretically confirmed that methyl substitution at the hydroxyl carbon of β-hydroxyketones causes a small enhancement in rates. The theoretical investigations of the mechanism and the rate constants are in agreement with the experimental results. © 1997 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 62 (1997), S. 13-21 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An analysis of the anisotropic Heisenberg model is carried out by solving the Bethe ansatz solution of the model numerically as a function of the anisotropy parameter for finite N. A brief introduction to the limit of the infinite chain is presented. The energy for a few special limiting cases of the anisotropy parameter in the Hamiltonian are worked out. Numerical results for finite cycles as well as for the infinite chain are given. Comparison can then be made with the case of finite increasing N. © 1997 John Wiley & Sons, Inc.
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  • 181
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    International Journal of Quantum Chemistry 62 (1997), S. 47-53 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The MELD program is employed to evaluate the Slater average potential v(r) felt by an electron at the point r within an atom. The characteristic radius R of the atom is then defined by the classical turning point equation v(R) = -I, where I denotes the first ionization potential of the atom. The atomic radii defined in this way have a close correlation with the van der Waals atomic radii. © 1997 John Wiley & Sons, Inc.
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  • 182
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    International Journal of Quantum Chemistry 62 (1997), S. 77-88 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly accurate upper bounds for several 2Pe states of the Li isoelectronic series obtained by extensive Hylleraas-Cl calculations are given. The best value for the 22Pe state (1s2p2) of Li is -5.21373920 au. The evaluation of the occurring integrals is given explicitly. Additionally, we present some expectation values and isotope energies of the Li isoelectronic series. © 1997 John Wiley & Sons, Inc.
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  • 183
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    International Journal of Quantum Chemistry 62 (1997), S. 97-113 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Restricted geometry optimizations at the ab initio SCF level with the 3-21G basis set were employed to investigate the conformation space of flavone acetic acid (FAA) and its related compounds. All the conformations are produced from a conformation which is, according to our previous work, probably the active conformation in terms of antitumor activity shown by these compounds. Detailed studies on FAA were carried out while only brief discussions are made on the analogs. The main results obtained are that (1) FAA is a very flexible molecule, e.g., with the energy barrier up to about 3 kcal mol-1 from the reference conformation, the important torsional angle τ1 can change from 27.0° to 117.0°, τ2 from -168.0° to 2.0°, and τ3 from -50.0° to 30.0°; (2) the hydrogen-bonding effect plays an important role in determining lower-energy conformations; (3) among all the FAA conformations considered, some are active and some are inactive; (4) it seems that the analogs will have similar behavior to FAA when the torsional angle τ3 is restricted to the values which are around the equilibrium values; and (5) the hypothesis put forward previously has been further developed in this work. Now, we postulate that efficient charge transfers will lower the energy and that proper charge transfers will activate the molecule. There are mainly two different types of charge transfer corresponding to two different types of conformation, which are specified in this article. © 1997 John Wiley & Sons, Inc.
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  • 184
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    International Journal of Quantum Chemistry 62 (1997), S. 273-278 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analytical solutions to the Yukawa-like screened Coulomb nuclear attraction and electron repulsion molecular basic integrals, as well as to the basic integrals required to compute the virial coefficient, over Gaussian basis functions, are derived and cast into a practical closed form, suitable to interface with modern codes for the calculation of molecular electronic structure. © 1997 John Wiley & Sons, Inc.
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  • 185
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    International Journal of Quantum Chemistry 63 (1997), S. 1079-1089 
    ISSN: 0020-7608
    Keywords: large-order perturbation theory ; lie algebra ; three-body problem ; symbolic computations ; helium atom ; Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The method of o(4, 2) operator replacements is generalized. As a result, the series whose limiting values when the variable goes to  +∞ should correspond to the two-electron atom energies now have rational coefficients. This generalization allows one also to compute the series for the case of singlet S symmetry, a case which could not be considered in the previous original formulation of the method. Series with rational coefficients for the helium singlet and triplet S ground-state energy are calculated up to order 41 and 45, respectively. Moreover, symbolic computations also allow one to give the first few coefficients of these series for arbitrary values of the nuclear charge Z. Finally, a new method for analytic continuation to the limit  +∞ is presented for the energies of the helium singlet and triplet ground states.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1079-1089, 1997
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  • 186
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    International Journal of Quantum Chemistry 63 (1997), S. 1099-1106 
    ISSN: 0020-7608
    Keywords: metathesis reactions ; bond order ; free valence ; minimum energy path ; nonsynchronization ; Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A few simple atom-transfer reactions (i.e., Ȧ+X-A→A-X+Ȧ) are studied by quantum mechanical ab initio methods. Emphasis is given to the detailed analysis of density matrices rather than to the energetics. Results reveal that during these reactions a small free valence always develops on the migrating atom at the transition state. The barriers in these reactions arise from the greater extent of bond cleavage in the reactant than that of bond formation in the transition state. Analysis of bond orders estimated from bond lengths using Pauling's relation also leads to the fact that the bond-cleavage process is more advanced than is the bond-formation process in these reactions.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1099-1106, 1997
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  • 187
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    International Journal of Quantum Chemistry 62 (1997), S. 29-45 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The H2 interaction with the Pd dimer and trimer were studied using multiconfigurational self-consistent field (MC-SCF) calculations with the relativistic effective core potential (RECP); the correlation energy correction was included in the extended multireference configuration interaction (MRCI), variational and perturbative to second order. Here, we considered the Pd2 first six states: 3Σ+u, 1Σ+g, 3Πg, 3Δxy, 1Σ+u, and 3Σ+g. For them, the four geometrical approaches included were the side-on H2 toward Pd2, for the hydrogen molecule in and out the Pd dimer plane; the perpendicular end-on H2 toward Pd2; and the perpendicular end-on Pd2 to H2. The Pd2 ground state is 3Σ+u, which only captures H2 in the C2v end-on approach, softly relaxing the H(SINGLE BOND)H bond. The closed-shell 1Σ+g captures the H2 molecule in all the approaches considered: The side-on approach of this state presents deep wells and relaxes the H(SINGLE BOND)H bond, and the end-on approach captures H2 with a relatively longer H(SINGLE BOND)H distance and also a deep well. The 3Πg state was the only one which did not capture H2. For the triangular Pd3 clusters, H2 was approached in the C2v symmetry in and out of the Pd3 plane. In the triangular case, H2 was absorbed in both spin states, with deep wells and relaxing the H(SINGLE BOND)H distance. The linear Pd3 singlet and triplet states capture outside of the Pd3 and break the H(SINGLE BOND)H bond. © 1997 John Wiley & Sons, Inc.
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  • 188
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    International Journal of Quantum Chemistry 62 (1997), S. 89-96 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We presented a calculation of the total and partial decay widths of vibrational predissociation (VP) of the HeI2 molecule for low initial vibrational excitations from the lowest van der Waals (vdW) state with total angular momentum J = 0. A time-dependent golden rule wave-packet method was employed in our numerical calculations for the decay widths. The computed total decay widths, lifetimes, and rates of VP are in fairly good agreement with those extrapolated from the experimental data available. Predicted total decay widths as a function of initial vibrational levels exhibit a highly nonlinear behavior. These results demonstrate that a quantum mechanical decay mode for low vibrational excitation remains as well. The total propagation time needed in the time-dependent golden rule wave-packet calculations is much shorter than is the lifetime of the predissociation of HeI2. It is shown that the final-state interaction between the fragments is important for determining the final rotational-state distribution (partial decay width). We find that the major peak position in the final rotational-state distribution shifts to lower rotational energy levels with increase of the initial vibrational quantum number, which is evidently different from that for higher vibrational levels. This fact can be clearly explained by the dependence of the amount of kinetic energy released to the product degrees of freedom on the initial vibrational state. © 1997 John Wiley & Sons, Inc.
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  • 189
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    Biospectroscopy 3 (1997), S. 233-239 
    ISSN: 1075-4261
    Keywords: cyclodextrins ; diclofenac ; inclusion complexes ; chemical shifts ; 1H-NMR spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The interaction between diclofenac (sodium salt of 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid) and β-cyclodextrin in aqueous solution has been investigated by 1H-NMR spectroscopic technique. The technique is based on the shielding of the β-cyclodextrin and drug protons. The spectra showed upfield shifts of the β-cyclodextrin protons in the presence of diclofenac, and the diclofenac protons also shifted upfield in the presence of β-cyclodextrin. The changes in chemical shifts of suitable guest-host protons are consistent with the formation of an inclusion complex diclofenac/β-cyclodextrin. © 1997 John Wiley & Sons, Inc. Biospect 3:233-239, 1997
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  • 190
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    Biospectroscopy 3 (1997), S. 241-249 
    ISSN: 1075-4261
    Keywords: NMR ; vibrational spectroscopy ; 5-bromouridine ; base pairing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A multinuclear magnetic resonance and vibrational study on 5-bromouridine and its base pairing with guanosine and adenosine in deuterated dimethyl sulfoxide at different concentrations is reported. A dicarbonylic non-self-associated form is suggested for 5-bromouridine on the basis of the 1H-, 15N-NMR, and Raman data. When guanosine is added in equimolar amounts, a downfield shift of the (N3)H proton of 5-bromouridine and of the (N1)H and NH2 protons of guanosine is observed; these results can be interpreted, according to the Raman ones, considering that only a fraction of guanosine is “wobble base paired” with 5-bromouridine, whereas the remaining part is self-associated. When 5-bromouridine is mixed with adenosine, the proton chemical shift of the aminic NH2 of adenosine increases and the (N3)H iminic of 5-bromouridine moves downfield at a value higher than that observed for the 5-bromouridine-guanosine mixture. This behavior supports the hypothesis that 5-bromouridine interacts more with adenosine than with guanosine, but the results obtained are not able to establish which type of pairing (Watson-Crick or Hoogsteen) is present. Finally, the infrared spectrum of the solid 5-bromouridine: adenosine adduct, for which X-ray measurements of other authors suggested a Hoogsteen pairing, is reported and the observed bands are discussed. © 1997 John Wiley & Sons, Inc. Biospect 3: 241-249, 1997
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  • 191
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    Biospectroscopy 3 (1997), S. 253-257 
    ISSN: 1075-4261
    Keywords: infrared spectroscopy of human tissue ; squamous and glandular cervical epithelium ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Infrared spectra of cervical tissue, obtained by biopsy from the squamous-columnar junction, are reported. The spectral patterns observed for columnar tissue are quite different from those of squamous epithelium. Subsequently, the spectra observed for columnar cells in tissue samples were also detected in the spectra of exfoliated cells, indicating the presence of endocervical cells. The columnar or glandular cells exhibit spectral features similar to those observed for pure cervical mucus. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 253-257, 1997
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  • 192
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    Keywords: electrospray ; MALDI ; mass spectrometry ; peptides ; proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The tremendous progress in biochemistry and biotechnology has been made possible in part by recent advances in analytical methods, in particular mass spectrometry. With the introduction of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), mass spectrometry allowed the determination of the molecular weight of peptides and proteins with a much greater accuracy than achievable by traditional methods such as SDS-PAGE and biogel chromatography. In addition, these mass spectrometry experiments have become routine and can be performed within minutes. ESI and MALDI (in combination with enzymatic methods) can also provide vital structural data such as the amino acid sequence and the sites of posttranslational modifications for peptides and proteins with a sensitivity that competes favorably with other methods. The use of ESI and MALDI is not limited to peptides and proteins; analysis of oligonucleotides and oligosaccharides has been simplified by these techniques as well. For information about structurally significant noncovalent interaction between various types of biomolecules, ESI is probably one of the most convenient methods. Not surprisingly, we anticipate that the mass spectrometers with these ionization capabilities will soon become standard equipment in all pharmaceutical and biotechnology laboratories. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 259-280, 1997
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  • 193
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    Biospectroscopy 3 (1997), S. 299-306 
    ISSN: 1075-4261
    Keywords: DNA ; silica ; binding ; Raman spectroscopy ; infrared ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: We studied by infrared and Raman spectroscopy the interaction of calf thymus DNA with various types of silica particles, ranging in size from 7 nm to 60 μm. Preliminary experiments with different samples showed that substantial variations can take place in the 1000-1100 cm-1 region of the attenuated total reflection (ATR) spectrum of silica, where a strong band due to a stretching vibration of the Si-O groups occurs. The position and intensity of this band were found to be dependent on several parameters, such as the size distribution of the solid particles, their proximity to the surface of the ATR crystal, and their degree of packing after sedimentation from the aqueous suspension. Changes observed in the spectra of aqueous solutions of DNA interacting with silica particles are explained by a shift of the main silica band in the mixtures. This interpretation differs from that of a previous study, where important intensity variations of the DNA bands at 1086 and 1053 cm-1 were explained by the formation of hydrogen bonds between the silanol groups of silica and the phosphate groups of DNA. Raman spectra of aqueous solutions of DNA mixed with fumed quartz particles of an average size of 0.007 μm showed but a minor change in intensity (ca. 5%) of the DNA symmetric phosphate band, which supports the conclusion reached in our infrared study. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 299-306, 1997
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  • 194
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    Biospectroscopy 3 (1997), S. 329-329 
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: No abstract.
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  • 195
    ISSN: 1075-4261
    Keywords: doxorubicin ; intercalation ; resonance Raman ; SERRS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The interactions of doxorubicin and its derivatives, hydroxyrubicin and adriamycinone, with DNA were studied by resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The π-π interaction between the chromophore of the drug and DNA base pairs has been shown to downshift the skeletal stretching mode ∼ 1440 cm-1 by 8, 5, and 4 cm-1 for doxorubicin, hydroxyrubicin, and adriamycinone, respectively. The additional effects of intercalation with DNA on the RR and SERRS spectra for hydroxyrubicin are similar to those for doxorubicin. However, different effects are observed for adriamycinone. These results indicate that the sugar moiety is necessary to maintain the maximum van der Waals contact between the chromophore and the DNA base pairs and that the amine group in the amino sugar is more favored than the hydroxyl group. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 307-316, 1997
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  • 196
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    Biospectroscopy 3 (1997), S. 331-346 
    ISSN: 1075-4261
    Keywords: urinary calculi ; FTIR spectroscopy ; Raman spectroscopy ; infrared ; calculi analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The application of infrared and Raman spectroscopic techniques to the analysis of urinary calculi is reviewed and their relative efficiency and adaptability to routine analysis are discussed. Using the classification of urinary calculi based on their main constituents, infrared and Raman spectra of calcium oxalates, phosphates, uric acid, urates, and cystine are reported. Some characteristic bands are suggested as useful for analytical purposes. References to other constituents such as drugs are included. Although this review is aimed principally at human stones, it also extends to literature references dealing with urinary calculi from canine, feline, and equine animal species. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 331-346, 1997
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  • 197
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    Biospectroscopy 3 (1997), S. 317-323 
    ISSN: 1075-4261
    Keywords: growth hormone releasing peptide ; tryptophan ; 2-methyl tryptophan ; GHRP-6 ; hexarelin ; EP7458 ; ultraviolet photolytic degradation ; rate constants ; differential photolysis ; photolysis products ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Aqueous solutions of three tryptophan-rich growth hormone releasing hexapeptides, GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2), hexarelin (His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2), and EP7458 (His-D-Trp-Ala-2-Me-Trp-D-Phe-Lys-NH2), were exposed to varying durations of ultraviolet (UV) light. Using NMR spectroscopy, first-order rate constants for the UV photolytic degradation of the tryptophan(s)/2-methyl tryptophan residues within each peptide were obtained by plotting the decrease in the area of the indole N-H resonances with respect to UV photolysis time. A significant differential photolytic effect was observed between the two tryptophan residues of GHRP-6 and the tryptophan/2-methyl tryptophan residues of EP7458. A somewhat smaller differential photolytic effect was observed between the tryptophan/2-methyl tryptophan residues of hexarelin. In addition, the three peptides were degraded at different rates, suggesting that the effect of UV light on each peptide is dependent on whether a tryptophan or 2-methyl tryptophan is the second or fourth residue in the primary sequence. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 317-323, 1997
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  • 198
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    Biospectroscopy 3 (1997), S. 347-369 
    ISSN: 1075-4261
    Keywords: urinary calculi ; infrared spectroscopy ; kidney biopsy ; etiology ; papillary calculi ; drug-induced calculi ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Crystal-induced kidney disease is a frequent occurrence in human pathology. It is becoming more and more apparent that knowledge of kidney stone composition and structure appears to be the key for establishing the etiology of stone disease. A number of analytical methods may be applied to stone analysis, but only a few of them are able to quickly and easily provide extensive information on both stone structure and composition relevant for clinical diagnosis. More than 12,000 calculi were analyzed using a combination of microscopic examination, sequential infrared (IR) analysis by Fourier transform infrared spectroscopy (FTIR) of each part of stone, and quantification of all components present. We also investigated 50 biopsies using FTIR microscopy. Our results confirm that IR spectroscopy is a reliable and accurate technique for both molecular and crystalline identification. Some limitations of standard procedures, because of very small samples or due to absorption band overlap, can be solved using FTIR micromethod or a particular method like IR microscopy. In such cases, the spectrum identification must be conducted in different manners. Until now, spectral identification procedures based on computerized spectra libraries must be used with caution because of false results, mainly for mixtures of mineral compounds. Trained eyes always provide the best results for reading spectra from common stones. In routine practice, accurate identification of all components present in calculi is necessary for understanding urolithiasis mechanisms, but only semiquantitative assessment is sufficient to guide physicians toward establishing correct etiology. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 347-369, 1997
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  • 199
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    Biospectroscopy 3 (1997), S. 421-433 
    ISSN: 1075-4261
    Keywords: plant photoreceptor ; photoisomerization mechanism ; excited state lifetime ; fluorescence quantum yield ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Time-resolved absorption spectra of Pr phytochrome were obtained using a regeneratively amplified femtosecond titanium : sapphire laser system. The early time transient absorption spectra are comprised of prompt Pr photobleaching, stimulated emission, and excited-state absorption features that decay with a 24 ps time constant that matches the ground state appearance time of the primary photoproduct. Based on the 5 ns radiative lifetime calculated from the absorption and spontaneous emission spectra and the fluorescence quantum yield of 5.5 (± 0.5) × 10-3, we calculate an excited-state lifetime of 28 ps that agrees well with the directly determined lifetime. The transient absorption spectra are consistent with a primary photochemical reaction quantum yield of 0.15, and the absorption spectrum of the primary photoproduct closely resembles that of the low-temperature trapped intermediate, lumi-R. We conclude that the primary photoisomerization, which is believed to be a Z,syn → E,syn isomerization of the C15=C16 chromophore bond, occurs in 24 ps. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 421-433, 1997
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  • 200
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    Biospectroscopy 3 (1997), S. 435-444 
    ISSN: 1075-4261
    Keywords: transferrin ; Raman ; absorption ; mutants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: The resonance Raman (RR) data for a variety of transferrin samples were investigated to explore differences between the two active sites. The excitation wavelength dependence of the RR data in the low energy shift region (〈900 cm-1) for diferric transferrin (Fe2Tf) reveals extensive changes in the relative intensities for some of the peaks, indicating that the visible and near ultraviolet absorption of the Fe2Tf protein is composed of several distinct transitions. The identity of the low-energy vibrations was explored by comparison of the data from Fe2Tf, two different binding site mutants of the N-terminal site half transferrin molecule, Tf/2N, and Fe2Tf in which the normal binding site carbonate was replaced with C18O32-. The higher energy RR spectra of the various samples are quite similar, whereas the low-energy band patterns are strongly influenced by the mutations and isotopic substitution. Comparison of the RR data obtained from Fe2Tf, Tf/2N, and C-terminal monoferric transferrin reveals that the intensities and energies of the modes below 900 cm-1 are different for the two binding sites. This result helps reveal an isolated electronic transition for the N-terminal active site near 365 nm, where laser excitation yields selective enhancement of the low-energy N-terminal modes. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 435-444, 1997
    Additional Material: 7 Ill.
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