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  • 2000-2004
  • 1995-1999  (807)
  • 1998  (807)
  • General Chemistry  (643)
  • Analytical Chemistry and Spectroscopy  (163)
  • Nuclear reactions
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Years
  • 2000-2004
  • 1995-1999  (807)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 84 (1998), S. 199-206 
    ISSN: 1572-9672
    Keywords: Nuclear reactions ; Nucleosynthesis ; Abundances ; Stars:Evolution ; Interior ; Rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We first recall the observational and theoretical facts that constitute the so-called 3He problem. We then review the chemical anomalies that could be related to the destruction of 3He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of 3He in low mass stars and simultaneously account for the low 12C/13C ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of 3He/H in galactic HII regions and allow for high values of 3He observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-193X
    Keywords: Photocycloaddition ; Ring opening ; Oxetanes ; 1,2-Diols ; Alkyldealkoxylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring opening of 3-isopropyl-2-phenyl-3-oxetanol (2a) by various nucleophiles has been studied. In the presence of BF3 as a Lewis acid, a clean reaction at the less substituted C-4 position was observed and the corresponding 1,2-diols 6-11 and 21-23 were isolated in diastereomerically pure form (47-97% yield). Alkyl-, aryl-, alkynyl- and alkenyllithium compounds proved to be suitable carbon nucleophiles. Deprotonated thiols were used as sulfur nucleophiles. An alkoxide derived from benzyl alcohol and an amide derived from benzylamine reacted less readily under these conditions, yielding the 1,2,3-trifunctional compounds 24 (42% yield) and 26 (54% yield). Other 2-phenyl-3-oxetanols such as 2b and 2c can also be employed as electrophiles, whereas 2-anisyl derivatives preferentially undergo rearrangement reactions, as exemplified by the conversion of oxetane 16 to the hydroxy ketone 17 (84% yield). The superior behaviour of 3-oxetanols as compared to their silyl derivatives in reactions with nucleophiles became evident from the reaction of 3-silyloxyoxetane 1a with alkyllithium reagents. A β elimination occurred upon treatment with nBuLi, which, after pericyclic ring opening and addition of nBuLi, yielded the allylic alcohol 20.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-193X
    Keywords: Azoalkanes ; DBO ; Fluorescence quenching ; Exciplexes ; Hydrogen transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fluorescence of the DBO derivatives 1-3 is efficiently quenched by olefins and arenes, exciplex formation and hydrogen transfer operate as quenching mechanisms. The electron-accepting ester groups in the azoalkanes 1-3 promote significantly more effective quenching compared to the parent DBO. Steric hindrance accounts for the differences in the quenching efficiencies, but electronic effects dominate
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: Mannich bases ; γ-Amino alcohols ; Grob fragmentation ; (Z)-Alkenes ; Oxetanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quaternized γ-amino alcohols 5 derived from ternary iminium salts 2 are stereospecifically converted into both unsaturated aldehydes/ketones 6 with a (Z)-C—C double bond in a Grob-type fragmentation and highly functionalized oxetanes 7 by intramolecular substitution.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2201-2207 
    ISSN: 1434-193X
    Keywords: Antibiotics ; Asymmetric synthesis ; β-Lactams ; Michael additions ; Multicomponent reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium dialkylcuprates react either in a sequential one-pot or in a domino “three-component” fashion with chiral Michael acceptors, like Oppolzer's N-enoyl-2,10-camphorsultams 7 and 11 or ‘Evans’ N-enoyl-4-phenyl-1,3-oxazolidin-2-ones 8 and 13, and N-(methoxycarbonylmethylidene)(4-methoxyphenyl)amine 9 to afford the corresponding cis-3-alkyl-4-methoxycarbonyl-1-(4-methoxyphenyl)azetidin-2-ones 10, 14-15 in overall yields of 40-67% and enantiomeric excesses of 91-99%.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2229-2235 
    ISSN: 1434-193X
    Keywords: 3-Nitro-ω-benzylideneacetophenone ; Carbanions ; Michael addition ; Intramolecular vicarious nucleophilic substitution of hydrogen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3-Nitro-ω-benzylideneacetophenone (1) reacts with carbanions containing leaving groups to give addition products to the electrophilic side chain. As a result of conjugated addition and subsequent intramolecular vicarious nucleophilic substitution of hydrogen (VNS) in the nitroaromatic ring of 1 in the position para to the nitro group, 4-cyano-7-nitro-3-phenyl-1,2,3,4-tetrahydronaphthalen-1-one and 4-cyano-7-nitro-3-phenylnaphth-1-ol are obtained. Smooth intramolecular VNS in the position para to the nitro group was observed for 4-chloro-1-(3-nitrophenyl)-3-phenyl-4-(p-tosyl)butanol.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1434-193X
    Keywords: Conformation analysis ; Electrochemistry ; Nitrogen heterocycles ; Dimerization ; Mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In aqueous media the one-electron reduction of the title compounds on a mercury pool generally gives rise to three dimers, which are distinguishable by HPL chromatography. From spectroscopic analyses it has been possible to propose a structure for these conformers and their stability has been studied. Two conformers are unstable, yielding the third conformer. A mechanism is proposed for this transformation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 837-846 
    ISSN: 1434-193X
    Keywords: AZT ; cycloSal-pro-nucleotide ; Prodrugs ; Nucleotide delivery ; HIV chemotherapy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of our cycloSaligenyl- (cycloSal) pronucleotide concept to the approved anti-HIV dideoxynucleoside 3′-azido-3′-deoxythymidine AZT (1) is reported. This pro-nucleotide concept has been designed to deliver the corresponding 3′-azido-3′-deoxythymidine monophosphate AZTMP (2) by selective chemical hydrolysis from the lipophilic precursors cycloSal-AZTMP 4a-h. All derivatives 4a-h were synthesized using differently substituted salicyl alcohols 7a-h as starting materials. In hydrolysis studies, compounds 4 decomposed selectively releasing AZTMP (2) and the salicyl alcohols 7 following the designed tandem reaction. Furthermore, due to the electronic properties introduced by substituents, the half-lives of the triesters 4 could be ajusted over a wide range. Phosphotriesters 4 exhibited considerable biological activity in HIV-1 and HIV-2 infected wild-type human T-lymphocyte (CEM/O) cells, whereas, contrary to our expectations, nearly all activity was lost in HIV-2 infected thymidine-kinase-deficient CEM cells.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1434-193X
    Keywords: N-Alkylation ; Diketopiperazine building block ; Peptidomimetics ; RGD analogues ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As a new scaffold for peptidomimetic synthesis, a highly constrained bifunctional diketopiperazine, 4, has been prepared by smooth N-alkylation with tert-butyl bromoacetate. As a first application, we describe herein the synthesis of new peptidomimetics of the Arg-Gly-Asp (RGD) sequence. The product 30, which shows a selective platelet-aggregation inhibiting activity, can be used as a lead for the preparation of more potent products.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 871-876 
    ISSN: 1434-193X
    Keywords: Dioxirane ; Homolysis, induced ; Aminoxyl ; Oxidation ; Spin-trapping ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the reactions of dimethyldioxirane (1a) and methyl(trifluoromethyl)dioxirane (1b) with 2,2,6,6-tetramethylpiperidinyl-1-oxyl (2) (TEMPO) in acetone, the corresponding methoxyamine 1-methoxy-2,2,6,6-tetramethylpiperidine (5) is produced in ≥98% yield, both in air and under N2, and in the absence or presence of a hydrocarbon (adamantane). Kinetic experiments show that aminoxyl 2 triggers the radical decomposition of the dioxirane, in addition to scavenging methyl radicals derived therefrom. The reactions of an aminoxyl less prone to oxidation, namely 1,2-dihydro-2-methyl-2-phenyl-3H-indol-3-one-1-oxyl (4), with dioxiranes 1a and 1b in acetone have also been studied. In these cases, not only is the corresponding methoxyamine 8a produced (yield 12-16%), but quinoneimine-N-oxides 10 (yield 12-21%) and 11 (yield 18-19%) are also formed. Furthermore, significant amounts (8-14%) of the amine 9 (the product of deoxygenation of 4) can be isolated. These observations provide useful information concerning the free-radical mechanism that follows the initial attack by the aminoxyl at the dioxirane.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2373-2377 
    ISSN: 1434-193X
    Keywords: Charge-transfer fluorescence ; Fluorogenic probe ; Fluorescence labelling ; Maleimide group ; Solvatochromism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural modification of the highly fluorescent donor-bridge-acceptor molecule “Fluoroprobe” (FP) is shown to extend the excitation window to longer wavelengths. The resulting “Fluorotrope” (FT) shows appreciable absorption in the 350-420-nm range, so that visible (blue) light can be used for excitation. Further functionalization with a maleimide group results in the novel fluorogenic reagent MaleimidoFluorotrope (MFT) which yields fluorescent adducts with amines, thiols and other reactive groups that add to the double bond of the maleimide. The fluorescence wavelength of these adducts is extremely sensitive to the polarity and mobility of the medium.
    Additional Material: 4 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2379-2387 
    ISSN: 1434-193X
    Keywords: β-Peptides ; Polylithiation of peptides ; Li-enolates of peptides ; Back-bone alkylation of β-peptides ; Diastereoselective alkylation of β-peptide enolates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of N-Boc-protected β-tripeptide derivatives with or without N-methyl groups and with free or Me-ester-protected C terminus has been prepared (8-14, 16, 17). As with α-peptides (→ A), the β-peptide derivatives can be polylithiated (→ B, C). No epimerization of stereogenic centers and no β elimination (exception 17 → 24) is observed upon treatment with bases as strong as tBuLi. The C terminal ester Li-enolate moiety of tetralithio β-tripeptides (cf. C) can be selectively alkylated with methyl, benzyl and allyl halides, and with tert-butyl bromoacetate in yields ranging from 35-80% (8 → 18, 14 → 20-23).
    Type of Medium: Electronic Resource
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  • 13
    ISSN: 1434-193X
    Keywords: Natural products ; Steroids ; Chenodeoxycholic acid ; Brassinosteroid analogues ; Biological activity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and spectroscopic characterization of two new bioactive analogues of brassinosteroids with a 24-hydroxylated cholanic side chain, an A/B ring cis-junction and oxygenated functions in C-7 is described.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2409-2416 
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Rearrangements ; Reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of 1,2-benzodithiino[5,4,3-cde][1,2]benzodithiin-2,7-diamine (1) and dithio-bridged benzidine 2 have been achieved. The starting material for the synthesis of 1 was 1,3-diiodo-5-nitrobenzene (15) which was transformed by conventional means into 1,2-bis[3,5-bis(ethylthio)phenyl]diazane (19). The benzidine rearrangement of 19 in the presence of HBF4 at -30 °C yielded 4,4′-diamino-2,2′,6,6′-tetraethylthiobiphenyl (20) in 50 % yield. Treatment of 20 with sodium in ammonia and work-up in the presence of air yielded 1. The latter compound could be reduced with LiAlH4 to the tetrathiol 20a. The starting material for the preparation of 2 was 3-chloro-1-iodo-5-nitrobenzene (23), a side product of the preparation of 15. It was transformed analogously to the preparation of 1 into 1,2-bis(3-ethylthiophenyl)diazane (28). The benzidine rearrangement of 28 in presence of HBF4 at -30 °C afforded 4,4′-diamino-2,2′-bis(ethylthio)biphenyl (29) in 49 % yield. Treatment of 29 with sodium in ammonia and work-up under aerobic conditions yielded 2. Quantitative reduction of 2 to the thiol 29a could be achieved with LiAlH4. The reversible electrochemical reduction of 1 on unmodified glassy carbon electrodes leads to a product to which the structure of 3 was assigned.
    Additional Material: 5 Ill.
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  • 15
    ISSN: 1434-193X
    Keywords: N-Heterocycles ; Porphyrins ; Radical cations ; N-Dealkylation ; Stereoelectronic effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evidence for a stereoelectronic inhibition of deprotonation of the radical cation of N-benzylpiperidine is presented. This stereoelectronic effect, which is due to the cyclic structure of the precursor, provides a tool to differentiate hydrogen-atom- versus electron-transfer routes in the biomimetic oxidative N-dealkylation of tertiary amines: the electron-transfer route appears to be the operating mechanism.
    Additional Material: 1 Ill.
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  • 16
    ISSN: 1434-193X
    Keywords: Colchicine ; 10-Ethylthiocolchicide, diene properties of ; π-Facial diastereoselectivity ; Consecutive [4+2],[3+2] cycloadditions ; Atropisomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloaddition reactions of the facially dissymmetric diene moiety of (-)-(M,7S)-colchicine (5) and (-)-(M,7S)-10-ethylthiocolchicide (9) to various alkynes have been studied. With 5 and the dienophilic benzyne (3), dimethyl acetylenedicarboxylate (DMAD) (4) and cyclooctyne (6) as starting materials all cycloadditions could be realized with high regioselectivity at the 8,12-positions of the alkaloid. The approach of the dienophiles preferentially occurred toward the syn π-face of the diene. In contrast to the cycloaddition mode of 5 the ethylthiocolchicide 9 surprisingly reacted in a different manner. With benzyne as starting material a novel [3+2] cycloaddition of the thioenol ether moiety of 9 towards the dipolarophilic benzyne is supposed, affording the unexpected colchicide 10 after [1,5]H shift of the primarily formed cycloadduct followed by cleavage of the C-S linkage. With DMAD (4) and cyclooctyne (6) the reaction course is more complex. In a consecutive [4+2]/[3+2] cycloaddition (or vice versa) followed by a thermally induced cycloreversion of a not identified intermediate DMAD (4) gives rise to the polycyclic thiophene derivative 13 and the novel allocolchicinoid 14. In a similar way cyclooctyne (6) yielded three products, the thiophene-annulated homobarrelenones 18 and 19 and the tetracyclic allocolchicinoid 21. The structures of the novel colchicine derivatives were assigned on the basis of spectral data, those of the cycloadducts 1 and 19 were verified by X-ray crystallography. For the unprecedented formation of the various allocolchicinoids by consecutive [4+2]/[3+2] cycloadditions plausible reaction pathways are suggested, as far as possible. In addition the inhibitory effects on the tubulin polymerization reaction in vitro of 10, 14, and 21 are reported.
    Additional Material: 2 Ill.
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  • 17
    ISSN: 1434-193X
    Keywords: Paclitaxel (Taxol®) ; Paclitaxel CD-ring ; High-pressure Diels-Alder reactions ; Furan cycloadditions ; Ether cleavage in 7-oxabicyclo[2.2.1]heptanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high-pressure promoted Diels-Alder reactions between several furans and citraconic anhydride have been studied and the cycloadducts obtained have been explored in new straightforward routes to the CD-ring fragment of paclitaxel. The reaction between furan and citraconic anhydride afforded the exo cycloadduct diastereoselectively, whereas a variety of 2-substituted furans afforded approximate 1:1 mixtures of exo regioisomers. Separation of both regioisomers was accomplished after either diastereoselective esterification or regioselective reduction of the anhydride function. Ether cleavage of the bicyclic compounds by either high-pressure promoted ether cleavage or Boord elimination afforded several potential CD-ring precursors which can be used in the total synthesis of paclitaxel analogues.
    Additional Material: 2 Ill.
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  • 18
    ISSN: 1434-193X
    Keywords: Camphoracetyl chloride ; Lactols, fused ; Lactones, fused ; Pseudoacid chlorides ; Reagents, stereoselective ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: endo-Fused lactone 3 was obtained in high yield from the camphoracetic acid 2 with thionyl chloride and a subsequent reduction of intermediate 5 with tributyltin hydride. The structure of 5 was elaborated and some aspects of the mechanism of its formation and reactivity were investigated. Lactone 3 serves as key intermediate for lactol 1 which is a useful reagent in racemate resolution and asymmetric synthesis.
    Additional Material: 1 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2609-2615 
    ISSN: 1434-193X
    Keywords: Supramolecular chemistry ; Domino reactions ; Bipyridines ; 1,x-Cyclohexanediones ; Mannich bases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A one-pot reaction using 1,x-cyclohexanediones, a Mannich base (or its hydrochloride), and ammonium acetate delivers novel pyridines or 3,3′-bridged bipyridine compounds 8, 16, 18, 20, and 22. This strategy offers a great flexibility in the design of new building blocks, e.g. in supramolecular chemistry and underlines the efficiency of domino reactions.
    Additional Material: 1 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2603-2607 
    ISSN: 1434-193X
    Keywords: Fluoro analogs of vitamin A ; Horner-Wittig reaction ; Fluoroisoprenoid building blocks ; Stereoselectivity ; Hydrolysis of chlorofluorocyclopropanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved method for the preparation of ethyl 2-fluoro-3-methyl-2-butenoate (3) is described. The two stereoisomers [(E)-4 and (Z)-4] obtained after γ-bromination can be separated and can be individually converted into the corresponding diethyl phosphonates. The PO-ylides generated by α-deprotonation of the latter lose their stereochemical integrity by rapid torsional equilibration of the ester tail. Thus, Horner-Wittig reactions accomplished with benzaldehyde and (Z)- or (E)-(β-ionylidene)-acetaldehyde lead inevitably to stereorandomization at the terminal, ethoxycarbonyl-bearing double bond affording (E)- and (Z)-isomers in 50:50 to 15:85 ratios, depending on the reaction conditions. The new double bond, however, is formed with perfect trans-selectivity.
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  • 21
    ISSN: 1434-193X
    Keywords: Alkaloids ; Total synthesis/Pumiliotoxin ; PTX-C ; PTX isomers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the synthesis of pumiliotoxin C (1a) and related stereoisomeric compounds 1c-1f. Starting from (+)- or (-)-3-methylcyclohexanone (6a,b), the oxo esters 7a and 7b were prepared. Condensation with (+)- or (-)-3-aminohexanol (8a,b) gave the stereoisomeric 3-aminoacrylates 9a, 9b and 9c. The hydroxy group of the amino-acrylates was transformed into bromide using the tosylate method. Cyclization of the bromides led to unsaturated quinoline ring systems. Finally, decarboxylation and catalytic hydrogenation gave the different cis- and trans-fused stereoisomeric alkaloids of the pumiliotoxin C type. The structures were verified by X-ray analysis.
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  • 22
    ISSN: 1434-193X
    Keywords: Lawesson's reagent ; Thiolation of cyclic ketones ; Anchimeric effect ; cis-Bicyclo[3.3.0]octane-3,7-diones ; 9-Thiatricyclo[3.3.1.03,7]nonane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple and efficient approach to the 9-thiatricyclo[3.3.1.03,7]nonane ring system (5) has been found by treating cis-bicyclo[3.3.0]octane-3,7-diones (1) with Lawesson's reagent or phosphorus pentasulfide. When dione 1 is treated with Lawesson's reagent tetramethyl 3(4aH)oxo-1,4-dihydrophenanthro[9,10-a]pentalene-1,2,4,4a-tetracarboxylate (6) is obtained as a by-product as shown by X-ray structural analysis.
    Additional Material: 1 Ill.
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  • 23
    ISSN: 1434-193X
    Keywords: Pyrazolidin-3-ones ; Optical activity ; Asymmetric synthesis ; Ring transformation ; Hydrazines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure α-alkylidenelactones 7 were prepared by a Wittig reaction from α-bromolactones 4 and chiral aldehydes 6. Compounds 7 react with hydrazines 9 by stereoselective Michael-like addition and ring-chain transformation affording optically active 4-(ω-hydroxyalkyl)pyrazolidin-3-ones 11.
    Additional Material: 5 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2673-2676 
    ISSN: 1434-193X
    Keywords: Aromatic aldehydes ; Pinacol coupling ; Radical reactions ; Reagent control ; Titanium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel concept for conductingtransition-metal-catalyzed radical reactions that allows highly diastereoselective titanocene-catalyzed pinacol couplings is described.
    Additional Material: 4 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2677-2682 
    ISSN: 1434-193X
    Keywords: Terpenoid lactones ; Antifeedants ; Limonene ; Claisen rearrangement ; Iodolactonization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four enantiomeric pairs of spirolactones were obtained in a four step synthesis from (+) and (-) limonene. The Claisen rearrangement and iodolactonization were the key steps of the syntheses presented. The structures of products were confirmed by X-ray crystallography of 11, 18b, and 19.
    Additional Material: 3 Ill.
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  • 26
    ISSN: 1434-193X
    Keywords: Phosphole ; Phosphanorbornadiene ; Stille cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of alkynylstannanes with 1-phenyl-3,4-dimethylphosphole at 150 °C affords the corresponding 2-stannyl-1-phosphanorbornadienes (2a, b), in fair yield. Oxidation under mild conditions affords the corresponding phosphane oxides (3a, b), whereas more drastic conditions (H2O2, 15% in toluene at 80 °C) induce the oxidative cleavage of the P-CH2 bond of the bridge to give a bicyclic phosphinate such as 4. Treatement of 4 by iodine leads to a tin → iodine exchange. The X-ray crystal structure analysis of the resulting 1-phospha-2-oxabicyclo[2.2.2]octa-5,7-diene 1-oxide confirms the functionalisation at the α-position and the relief of ring strain taking place upon insertion of oxygen into the P-CH2 bond of the norbornadiene. The 2-stannyl-1-phosphanorbornadiene 1-oxides (3a, b) readily undergo tin → iodine exchange. The resulting 2-iodo derivatives (6a, b) can be cross-coupled with 2-furyl-, 2-thienyl-, 2-pyrrolyl-, phenylethynyl-, and vinyl-tributylstannanes to give the corresponding 2-functional 1-phosphanorbornadiene 1-oxides in excellent yields (80-95%)
    Additional Material: 1 Ill.
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  • 27
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Density functional calculations ; Cycloadditions ; Dihydropyrans ; Enantioselective oxidations ; Sulfur heterocycles ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 4-benzylidene-3-oxo[1,3]oxathiolan-5-ones 13-15, which were derived from the 3-oxo[1,3]oxathiolan-5-ones 9-11 by Knoevenagel condensation with the aldehydes 12, cyclize in an intramolecular hetero Diels-Alder reaction with high yield and excellent endo/exo as well as induced diastereoselectivity to give the hetero Diels-Alder adducts 16-18. The preferred formation of the Knoevenagel products 13-15 with a (Z) configuration was predicted with DFT calculations (B3LYP-6-311+G*) using the model systems 28 and 29. In addition B3LYP-6-31G*/sB3LYP/3-21G(*) calculations on transition structures for the hetero Diels-Alder reaction of 29 and 30 allowed a good correlation with the experimental results, which show that an endo attack of the dienophile syn to the S-O group in 13-15 leads to the main products.
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  • 28
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    Liebigs Annalen 1998 (1998), S. 2759-2767 
    ISSN: 1434-193X
    Keywords: Phosphorus phthalocyanines ; Triazatetrabenzcorroles ; Dihydroxyphosphorus(V) phthalocyanine hydroxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The previously reported reaction of phthalocyanines [H2(pc)] with PBr3, which was claimed to give a phosphorus(III) phthalocyanine “(PcPIII)”, has been reinvestigated in detail with both unsubstituted and alkyl-substituted phthalocyanines, 1-4. The products exhibit unusual electronic and mass spectra compared to normal phthalocyanines and have been identified as oxophosphorus(V) triazatetrabenzcorroles 5-8. The corresponding dihydroxyphosphorus(V) phthalocyanine hydroxides 9-12 have also been synthesized for the first time by insertion of phosphorus(V) into phthalocyanines and have been characterized in detail. The different reactivities of PBr3 and POX3 (X = Cl, Br) toward phthalocyanines are discussed.
    Additional Material: 3 Ill.
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  • 29
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    Liebigs Annalen 1998 (1998), S. 2769-2773 
    ISSN: 1434-193X
    Keywords: Rubicenes ; Cyclization ; Polycyclic aromatic hydrocarbons ; Arenes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of novel disubstituted rubicenes 1a-k is described. Starting from 1,5-dichloroanthraquinone and aryllithium reagents 3, the diol adducts 4 are reduced and the resulting diarylanthracenes 5 are cyclized to afford the title compounds in fair to good overall yield.
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  • 30
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 37-41 
    ISSN: 1434-1948
    Keywords: Tripodal P ligands ; Rhodium ; Water-soluble complexes ; Immobilization ; Biphasic hydroformylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the water-soluble tripodal phosphane ligand cis,cis-1,3,5-(PPh2)3-1,3,5-[CH2(OCH2CH2)xOCH3]C6H6 (x = 30-160) (5) has been achieved in a four-step reaction sequence. The alcohol Mo(CO)3[cis,cis-1,3,5-(PPh2)3-1,3,5-(CH2OH)3C6H6] (1) is converted to the corresponding alcoholate 2, which forms the polyethylene glycol derivative 3 in a polyaddition reaction with oxirane. After methylation of the end groups of 3, the ligand 5 is obtained by a combined photochemical/oxidative demolybdenation reaction. The water-soluble tripodal phosphane 5 and the methoxymethyl functionalized tripodal ligand 6 react with Rh(PPh3)3(CO)H to form the water-soluble and water-insoluble rhodium carbonyl hydrido complexes 5a and 6a, respectively. The catalytic activity of the rhodium complex 5a in the hydroformylation of 1-hexene was found to be comparable in a single-phase system (1-hexene/methanol) with that in the biphasic system (1-hexene/water). Only traces of alcohol were found, which demonstrates that the catalyst 5a displays higher selectivity in hydroformylation than in hydrogenation.
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  • 31
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    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 55-59 
    ISSN: 1434-1948
    Keywords: Arsaalkenes ; Arsenic ligands ; Carbonyl complexes ; Chromium ; Iron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of equimolar amounts of the metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] (1) with the carbonyl complexes [Ni(CO)4], [Fe2(CO)9], and [{(Z)-cyclooctene}Cr(CO)5], respectively, affords the adducts [(η5-C5Me5)(CO)2FeAs{M(CO)n}=C(NMe2)2] with [M(CO)n] = [Ni(CO)3] (2); [Fe(CO)4] (3), and [Cr(CO)5] (4). These feature η1 coordination of the arsaalkene ligand via the arsenic atom. The molecular structures of the complexes 3 and 4 have been determined by X-ray diffraction analyses.
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  • 32
    ISSN: 0935-6304
    Keywords: Epoxytriacylglycerols ; high temperature gas chromatography ; hydroxytriacylglycerols ; ketotriacylglycerols ; lipids ; negative chemical ionization mass spectrometry ; SOP-50 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Five seed oils consisting of unusual triacylglycerols have been examined by high temperature gas chromatography using glass capillary columns coated with the stationary phase SOP-50 (50%-diphenyl-50%-dimethylpolysiloxane, methoxy-terminated). The investigated hydroxy, epoxy, and ketokonjuene triacylglycerols were first derivatized in order to permit analysis by high temperature gas chromatography. Structural elucidation of the intact triacylglycerols was performed with high temperature gas chromatography/negative chemical ionization-mass spectrometry using NH3 as a reagent gas. Individual derivatized lipid species with a molecular weight up to 1176 g/mol could be identified.
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  • 33
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    Journal of High Resolution Chromatography 21 (1998), S. 169-174 
    ISSN: 0935-6304
    Keywords: CZE ; detection limit ; signal-to-noise ratio ; correlation chromatography ; reproducibility ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Poor signal-to-noise ratios and analytical reproducibility in capillary electrophoresis were improved by application of multiple injections of the same sample at (pseudo) randomly chosen time moments. One order of signal-to-noise ratio improvement was achieved in practice using an in-house developed computer-controlled pneumatic sampler. However, it is demonstrated here that better implementation of the capabilities of multiple input requires that the detector signal noise be “pre-whitened”, i.e. spikes, baseline drift, oscillations etc. must be removed from the detector signal before transforming it to the electropherogram in the common form. Such filtering of the detector signal was realized by implementing iterative, menu-driven software written in Matlab, a high-level programming language.
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  • 34
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    Journal of High Resolution Chromatography 21 (1998), S. 181-184 
    ISSN: 0935-6304
    Keywords: Trace analysis, atmospheric ; digital signal processing ; signal to noise reduction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 35
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    Journal of High Resolution Chromatography 21 (1998), S. 189-192 
    ISSN: 0935-6304
    Keywords: Chiral stationary phases ; pyrethroic acids ; enantiomer separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 36
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    Journal of High Resolution Chromatography 21 (1998), S. 193-196 
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; dissolving solvent selection ; optimization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 37
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    Journal of High Resolution Chromatography 21 (1998), S. 201-208 
    ISSN: 0935-6304
    Keywords: PAN ; peroxyacetyl nitrate ; alkyl nitrate ; chlorinated hydrocarbons ; halocarbons ; capillary GC-ECD ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A cryogenic preconcentration/high-resolution gas chromatographic technique has been developed for the rapid, simultaneous quantitation of C1-C4 organic nitrates and halocarbons in ambient air. Whole-air samples are collected in TedlarTM bags by an evacuated-chamber method. Samples were stable in 0.010-cm-thick bags for 24 h if they were immediately stored in a freezer at -25°C. Analytes in a 50-cm3 air sample were efficiently preconcentrated on fused-silica beads at -180°C and thermally desorbed at 30°C. High-resolution gas chromatography with a cross-linked polydimethylsiloxane fused-silica capillary column and an electron-capture detector were used for separation and quantitation of the analytes. An analysis time of about 12 min was facilitated by sample cryofocusing at -180°C and oven temperature programming. Recoveries of the analytes by the evacuated-chamber method were better than 95%. The sensitivity of the technique for sample volumes of 50 cm3 is in the sub-parts-per-trillion by volume (ppt[v]) range for many of the analytes, with an average precision of about ±5% for analytes at levels of about 10 ppt(v).
    Additional Material: 4 Ill.
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  • 38
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; enantiomer separation ; hydroxypropyl-β-cyclodextrin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Following an extended screening project, 86 racemic drugs were investigated by capillary zone electrophoresis in the presence of the chiral solvating agent (CSA) hydroxypropyl-β-cyclodextrin. A total of 42 drugs out of 86 tested was thereby separated into enantiomeric pairs. Statistical analysis of the numerous experiments performed un der identical conditions reveals a loose correlation of the migration separation factor (αm) with the migration retardation factor (Rm). For a subset of 23 drugs, a drop in the concentration of the CSA was also studied, showing the way to further optimization.
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  • 39
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    Journal of High Resolution Chromatography 21 (1998), S. 253-257 
    ISSN: 0935-6304
    Keywords: Edible oils ; lipids in foods ; HPLC ; Polycyclic Aromatic Hydrocarbons (PAHs) ; off line LC-LC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 40
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    Journal of High Resolution Chromatography 21 (1998), S. 234-240 
    ISSN: 0935-6304
    Keywords: Micellar electrokinetic capillary chromatography ; electroosmotic migration ; electrophoretic migration of micelle ; retention mechanism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In the present work, four organic modifiers, viz. urea, dioxane, methanol, and tetrahydrofuran, were comparatively and systematically studied in terms of their effects on electrokinetic migration behavior and the retention mechanism of homologous solutes in MECC. The results showed that the electroosmotic mobility, μeo, and the electrophoretic mobility of a micelle, μep,mc, decrease linearly with increasing organic modifier concentration. The ability of organic modifiers to lower μeo is greater than their ability to lower μep,mc. The negative values of the slopes of these linear relationships, Deo and Dep,mc, increase along the series the order urea 〈 methanol 〈 dioxane 〈 tetrahydrofuran. The logarithm of the capacity factor (ln k′) of uncharged homologous solute, which is mainly determined by the hydrophobic interaction, decreases linearly with increasing organic modifier concentration, due not only to the decrease in the partition coefficient but also to the decrease in the phase ratio. A linear relationship was observed between the slope of the plot of ln k′ vs. organic modifier concentration and the carbon number of homologous compound. The slope of such a relationship can characterize the hydrophobicity of the organic modifier. The hydrophobicity of such organic modifiers is also found to increase along the series urea 〈 methanol 〈 dioxane 〈 tetrahydrofuran.
    Additional Material: 7 Ill.
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  • 41
    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.
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  • 42
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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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  • 43
    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.
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  • 44
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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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  • 45
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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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  • 46
    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.
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  • 47
    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
    Additional Material: 4 Ill.
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  • 48
    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
    Additional Material: 1 Ill.
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  • 49
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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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  • 50
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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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  • 51
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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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  • 52
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    Journal of High Resolution Chromatography 21 (1998), S. 435-439 
    ISSN: 0935-6304
    Keywords: Micellar Electrokinetic Chromatography (MEKC) ; counter pressure moderated MEKC ; migration time window ; peak resolution and peak capacity in MEKC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The influence of a hydrostatic counter pressure on basic mobility equations in MEKC was analyzed theoretically and investigated experimentally. Taking into account the influence of counter pressure, the modified mobility equations predict a decreased migration time ratio t0/tMC, which was confirmed by results obtained in SDS-MEKC separation of a homologous series of n-alkyl phenyl ketones. As a result, the migration time window could be enlarged in a simple way without having to change the chemistry of the system. Although counter pressures reduce peak efficiency in MEKC by disturbing the plug profile, the concomitant enlargement of the migration time window compensates for this effect. Especially for later migrating compounds, peak resolution could be enhanced at moderate counter pressures. The overall peak capacities within the whole migration window increases slightly when applying counter pressures up to 10 mbar.
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  • 53
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    Journal of High Resolution Chromatography 21 (1998), S. 445-449 
    ISSN: 0935-6304
    Keywords: chiral separation ; organic cation effect ; ethylamines ; ethanolamines ; basic drugs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper addresses the influence of small organic cations in the background electrolyte (BGE) on chiral separation by capillary zone electrophoresis (CZE). Seven basic drugs, viz. alprenolol, amphetamine, anisodamine, isoprenaline, pinacidil, synephrine, and verapamil were used as test compounds with hydroxylpropyl-β-cyclodextrin (HP-β-CD) as the chiral selector. Resolution of the chiral test compounds was studied at pH 2.5 in the presence of Tris, ethanolamine, diethanolamine, triethanolamine, diethylamine, and triethylamine, which exist in their cationic forms at this pH value. Among the six cationic additives studied, triethylamine is most effective in enhancing resolution. A tentative mechanism of the effect is proposed.
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  • 54
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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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  • 55
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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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  • 56
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    Weinheim : Wiley-Blackwell
    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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  • 57
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 587-591 
    ISSN: 0935-6304
    Keywords: capillary GC ; polymethoxyflavones ; citrus oil ; GC/MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The cold pressed peel oils of three species of citrus fruit, viz. sweet orange, tangerine, and grapefruit, have been examined for polymethoxyflavones by GC and GC-MS. Four GC column stationary phases were compared and separation of the six predominant orange oil polymethoxyflavones was obtained isothermally at 310°C in under ten minutes, including the resolution of the polymethoxyflavones from β-sitosterol. The nature of the stationary phase and the analysis temperature exercise dramatic effects on the resolution and elution order of the components, DB-35ms providing the best overall separation. A temperature programmed separation is also presented and the polymethoxyflavone composition of all three oils, as determined by GC-MS, is described. This is the first reported GC-MS study of the PMFs of these citrus species. While tangerine oil is as rich in polymethoxyflavones as orange oil, they are less abundant and occur at lower concentrations in grapefruit oil. Hydroxy-polymethoxyflavones were identified by GC-MS in tangerine oil. One hydroxy-pentamethoxyflavone, M+ = 388, identified in tangerine was also present at low levels in both orange and grapefruit oils. These results are compared with previous studies utilizing HPLC and GC.
    Additional Material: 6 Ill.
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  • 58
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 605-607 
    ISSN: 0935-6304
    Keywords: Reversed-flow MEKC ; separation according to polarity ; organic modifiers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reversed-flow MEKC, i.e. MEKC at low pHs to suppress the electroosmotic flow, was evaluated for the separation of some homologous series. At low pHs compared to MEKC, the elution order reverses and normal phase type migration is obtained. Moreover, the elution window is nearly infinite. Efficiencies are very high and reproducibilities in absolute migration times are acceptable (%RSD 〈 5). The influence of a series of alcohol modifiers was investigated.
    Additional Material: 2 Ill.
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  • 59
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 597-604 
    ISSN: 0935-6304
    Keywords: high temperature gas chromatography ; atomic emission detection ; microwave induced plasma ; compound independent calibration ; non-ionic surfactants ; alcohol ethoxylates ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---High temperature gas chromatography (HT-GC) coupled to atomic emission detection (AED) has been applied for the determination of alkyl chain distribution, mole average degree of ethoxylation and weight percent distribution of the corresponding homologues of alcohol ethoxylates without all the actual homologues being available as pure references. Based upon its constant elemental response, the HT-GC-AED system has been evaluated for its applicability to compound independent calibration within the homologous series of the alcohols and alcohol ethoxylates. Discrimination against high molecular weight components by gas chromatography requires conversion to the acetyl or trimethylsilyl derivatives. The latter includes introduction of the hetero atom silicon and thus allows monitoring of the silicon trace. Thus selectivity will be enhanced by excluding detection of compounds which do not react with the derivatization reagent. The method has been validated with the analysis of the technical product Brij 30, consisting of a mixture of alcohol ethoxylates with a vendor-specified mole average degree of ethoxylation of four. The experimental result yields a mole average degree of 4.0 ± 0.1 in the carbon, silicon and oxygen traces.
    Additional Material: 12 Ill.
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  • 60
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 608-612 
    ISSN: 0935-6304
    Keywords: propolis ; profiling ; CZE ; MEKC ; flavonoids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The usefulness of capillary electrophoresis (CE) with diode array detection for the profiling of Propolis, a hive product, is investigated. Water extracts of Propolis were analyzed with both capillary zone electrophoresis (CZE) at pH 7.0 and 9.3, and micellar electrokinetic chromatography (MEKC) with sodium dodecyl sulfate at pH 9.3. Characteristic profiles were obtained and several organic acids and preservatives could be identified by means of library comparison of the recorded UV spectra combined with addition of reference compounds to the extracts. The selectivity of the CZE and MEKC system differed considerably but the information obtained with both methods was similar. The dry residues of the water extraction were extracted with ethanol-water (70 : 30, v/v) and analyzed with the MEKC system to enable the separation of the more hydrophobic constituents of the Propolis samples. Complex profiles containing various well separated peaks were obtained allowing the identification of some interesting flavonoids. On the basis of the recorded CZE and MEKC profiles, the Propolis samples could be divided into two clearly different groups which are probably from a different origin.
    Additional Material: 4 Ill.
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  • 61
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 625-627 
    ISSN: 0935-6304
    Keywords: End-closure ; end-seal ; static coating ; glass and fused silica capillaries ; press-fit cap ; polyethylene closure ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 62
    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: ---Simultaneous element-selective detection of the halogens and carbon was accomplished with capillary gas chromatography coupled with microplasma mass spectrometry. The microplasma ion source was a radio frequency plasma contained inside the last 4-5 cm of the 0.32 mm i.d. fused silica capillary column. The ion source was located inside the high vacuum housing of the MS, and only the GC carrier gas (2.3 mL min-1 of helium) was used for plasma generation. Atomic ions were detected in the positive mode. Detection limits were in the low picogram area, and the selectivity to carbon ranged from 8×102 for fluorine to higher than 104 for the other halogens. By introduction of both hydrogen and oxygen as reagent gases, peak tailing was avoided by suppression of analyte reactions with the silica walls of the ion source. Special attention was given to the fluorine-selective detection due to an interfering background species at m/z 19, assumed to be H3O+ originating from the reagent gases. The background signal was minimized by careful control of the power level.
    Additional Material: 5 Ill.
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  • 63
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    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.
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  • 64
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    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.).
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  • 65
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    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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  • 66
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    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.
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  • 67
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    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.
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  • 68
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    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.
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  • 69
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    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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  • 70
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    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.
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  • 71
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    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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  • 72
    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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  • 73
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    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.
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  • 74
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    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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  • 75
    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.
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  • 76
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    Journal of High Resolution Chromatography 21 (1998), S. 11-17 
    ISSN: 0935-6304
    Keywords: Acridine-modified HPLC stationary phases ; ligand mobility ; fluorescence spectroscopy ; time-resolved fluorescence anisotropy ; solid state NMR spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ligand mobility of silica-based HPLC stationary phases modified by various surface coverages of acridine-9-carboxy(N-aminoethylaminopropyl)amide ligands was investigated by fluorescence spectroscopy, time-resolved fluorescence anisotropy measurements, as well as solid-state 13C-CP/MAS- and 1H-MAS-NMR spectroscopy. Rotational correlation times, τR, of the bound acridine fluorophore obtained from fluorescence anisotropy measurements are significantly longer in the bound phase, than in solution. Also, in time-resolved experiments anisotropies do not decay to zero. These results are interpreted in terms of wobble-in-cone ligand motion. The mobility of the fluorophore in the presence of liquid phase correlates strongly with the solubility of the model compound acridine-9-carboxy-n-butylamide in the same solvent. In the good solvent acetonitrile τR = 3.2 ns is found, whereas in methanol, τR 〉 80 ns is obtained. NMR measurements of the dry phase yield large linewidths, cross polarization constants, TCH, and spin-lattice relaxation times, T1ρH, shifting around the minimum in the correlation time curve. Both fluorescence and NMR data indicate medium to low ligand mobility. No difference in the mobilities of alkyl spacer and aromatic group is observed, probably due to the rigidity of the amide group.
    Additional Material: 6 Ill.
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  • 77
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    Journal of High Resolution Chromatography 21 (1998), S. 18-24 
    ISSN: 0935-6304
    Keywords: Reversed-phase HPLC ; capillary electrophoresis ; MALDI-MS ; whey proteins ; multiple peaks ; bovine serum albumin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Elution of a commercial sample of bovine serum albumin (BSA) in a reversed-phase (RP) HPLC system at room temperature gives a distorted peak. If a shallow gradient is used during elution a split peak is observed. The nature of the several parts of this multiple peak is studied using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), size-exclusion chromatography (SEC), amino acid analysis, re-elution in RP-HPLC of collected fractions, capillary electrophoresis (CE), and matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS). This study demonstrates that the split peak of BSA observed in these chromatographic conditions is due to the monomer, dimer and other aggregates existing in the commercial sample of the BSA used. Moreover, it is proved that typical RP-chromatographic conditions do not cause aggregation of BSA.
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  • 78
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    Journal of High Resolution Chromatography 21 (1998), S. 59-62 
    ISSN: 0935-6304
    Keywords: capillary electrophoresis ; mass spectrometry ; MALDI ; CE-MALDI ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 79
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    Journal of High Resolution Chromatography 21 (1998), S. 55-58 
    ISSN: 0935-6304
    Keywords: liquid chromatography-mass spectrometry ; electrospray ionization ; haloacetic acids ; trace analysis of environmental water samples ; waste water samples ; river water samples ; seawater samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Negative ionization electrospray liquid chromatography mass spectrometry was developed for the simultaneous determination of all nine haloacetic acids containing bromine and chlorine. Haloacetic acids were separated on a crosslinked polystyrene resin column using 3% acetic acid dissolved in acetonitrile:water (20:80) as mobile phase. The precision of this method varied from ±2.2 to ±7.1% for nine haloacetic acids. In addition, quantitative results obtained with spiked water samples at three different concentrations are described. The limit of detection of the proposed method using 200 mL of water samples was between 0.003 and 0.070 μg/L. This method was successfully applied to the trace determination of haloacetic acids in waste water, river water, and seawater.
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  • 80
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    Journal of High Resolution Chromatography 21 (1998), S. 63-64 
    ISSN: 0935-6304
    Keywords: Injection port performance ; comprehensive two-dimensional GC ; GC× ; GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 81
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    Journal of High Resolution Chromatography 21 (1998), S. 65-68 
    ISSN: 0935-6304
    Keywords: GC-MS ; rain ; roof runoff ; fatty acids ; phenols ; alkanes ; chlorinated compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 82
    ISSN: 0935-6304
    Keywords: gas chromatography, helium ionization detector (HID) ; formaldehyde ; atmospheric oxygenates ; volatile organic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two different gas chromatographic detectors, the helium ionization detector (HID) and the more commonly used flame ionization detector (FID), were used in parallel to compare their responses to a number of organic compounds. Atmospherically important oxygenated species were analyzed, as well as hydrocarbons and chlorinated and sulfur containing organics. The HID exhibited the better response to all compounds investigated, most notably to formaldehyde and higher oxygenates. A gas chromatographic system was developed to trap and analyze atmospheric organic compounds with HID detection. This required careful choice of the adsorbent material and removal of inorganic components (namely nitrogen and oxygen) before analysis. Real air samples were then taken and analyzed qualitatively for a range of olefinic and aromatic compounds.
    Additional Material: 6 Ill.
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  • 83
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    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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  • 84
    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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  • 85
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 107-112 
    ISSN: 0935-6304
    Keywords: Linalool; linalyl acetate ; enantioseparation by enantioselective gas chromatography ; enantiomer distributions in natural products obtained by different extraction processes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The enantiomeric distributions of linalool and linalyl acetate in various natural products are measured by enantioselective gas chromatography on alkyl-substituted cyclodextrins. Different plant cultivars were investigated by four extraction processes: steam distillation, solvent extraction, supercritical fluid extraction, and headspace analysis. Careful attention must be paid to linalool which undergoes partial racemization under certain processing conditions. In most cases, enantiomeric distribution is a powerful tool for authenticity testing.
    Additional Material: 1 Ill.
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  • 86
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 121-123 
    ISSN: 0935-6304
    Keywords: gas chromatography ; capillary columns ; column efficiency ; column comparison ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The correct meaning of the the term “utilization of the theoretical efficiency” vs. the “coating efficiency” is explained.
    Additional Material: 1 Tab.
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  • 87
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 125-127 
    ISSN: 0935-6304
    Keywords: multidimensional gas chromatography ; self-made connectors ; effluent splitting ; press fit connectors ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 88
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 133-136 
    ISSN: 0935-6304
    Keywords: GC ; analysis of vegetable oil ; petroselinic acid ; butyl esters ; 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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  • 89
    ISSN: 0935-6304
    Keywords: Enantioselective multidimensional capillary gas chromatography (enantio-MDGC) ; stable isotope ratio mass spectrometry (IRMS) ; multidimensional gas chromatography coupled on-line with isotope ratio mass spectrometry (MDGC-IRMS) ; calibration; isotope discrimination ; authenticity control ; authentication of genuine flavor components ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Multidimensional gas chromatography coupled on-line with isotope ratio mass spectrometry (MDGC-IRMS) is presented as a powerful method for origin-specific analysis. Scope and limitations of this sophisticated coupling technique are discussed with regard to accuracy and precision.
    Additional Material: 6 Ill.
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  • 90
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 161-168 
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; optimization ; mixture design ; DUP 654 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Capillary Electrochromatography (CEC) offers a rapid, economical, and efficient means for resolving nonionic compounds in the reversed phase mode on octadecylsilane (ODS) columns. A CEC optimization on a Hypersil ODS capillary column was employed to identify a suitable mobile phase for the pressure-driven (reversed phase ODS) separation of the anti-inflammatory 2-phenylmethyl-1-naphthol (DUP 654), and its related substances. The proportions of mobile phase modifiers methanol, acetonitrile, and water as well as pH were employed as variables in a stacked mixture design. Comparable response surface profiles were obtained for the CEC separations at pH 4 and pH 8. However, subtle differences were evident in the quality of separations obtained in the liquid chromatographic (LC) mode when using a specially-prepared column packed with exactly the same stationary phase as used in the CEC experiments. A mapping of the response surface for separations on a commercially available Hypersil ODS LC column revealed obvious differences. The differences indicate that the transfer of ODS based separation methods between CEC and LC involves more than simply transferring the conditions from one mode to the other.
    Additional Material: 7 Ill.
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  • 91
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 175-180 
    ISSN: 0935-6304
    Keywords: Supercritical Fluid Extraction (SFE) ; supercritical fluid chromatography ; solid trapping ; solvent trapping ; polymeric phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---One way of collecting extracted analytes after a supercritical fluid extraction (SFE) is to pass the depressurized fluid through a trap composed of a solid adsorbent. The influence of the adsorbent nature on the trap efficiency has been studied. First, the retention factors of each compound of a polarity test mix (tetracosane, naphthalene, fluoranthene, acetophenone, N,N-dimethylaniline, 2-naphthol, decanoic acid) have been determined on five high specific area (greater than 800 m2/g) polymeric phases by supercritical fluid chromatography (SFC). The comparison of this values with those obtained on octadecyl silica (ODS) showed that polymeric phases have the greatest retention power. After that, the efficiency of a solid trap filled with the greatest retention power polymeric adsorbent was evaluated by using pure carbon dioxide and 2.5%, 5%, 10%, and 20% methanol-modified carbon dioxide. As expected, this trap permitted a quantitative collection of all the former compounds even when a content as high as 10% of methanol was implemented. A solid trap filled with ODS adsorbent allowed quantitative collection of all the compounds only at a methanol content lower than 2.5%.
    Additional Material: 7 Ill.
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  • 92
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 185-188 
    ISSN: 0935-6304
    Keywords: Dill ether ; stereoselective synthesis ; dill ether stereoisomers ; enantioselective GC ; 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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  • 93
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 197-199 
    ISSN: 0935-6304
    Keywords: Chiral recognition of 2-pentanol enantiomers ; enantioselective interactions ; capillary gas chromatography ; permethylated-β-cyclodextrin ; 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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  • 94
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    Weinheim : Wiley-Blackwell
    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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  • 95
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    Weinheim : Wiley-Blackwell
    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.
    Additional Material: 7 Ill.
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  • 96
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 427-434 
    ISSN: 0935-6304
    Keywords: Linear solvation energy relationship ; retention ; mobile phase ; stationary phase ; additives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Linear solvation energy relationships (LSERs) were used to delineate which specific intermolecular interactions are responsible for changes in retention for a variety of well characterized analytes when acidic and basic additives were used in reversed phase HPLC. The effects of trifluoroacetic acid, triethylamine and a combination of trifluoroacetic acid and triethylamine on the LSERs were compared to those observed in the absence of additives. These effects were examined using four different mobile phase modifiers and five different stationary phases. Trifluoroacetic acid alone and in combination with triethylamine produced LSER regression coefficients nearly identical to those obtained with no additive present in the mobile phase. Triethylamine alone produced different LSER regression coefficients from the other systems unless the mobile phase contained trifluoroethanol as the mobile phase modifier, or the stationary phase consisted of a polymeric support.
    Additional Material: 3 Ill.
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  • 97
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 498-504 
    ISSN: 0935-6304
    Keywords: Nonaqueous solvents ; capillary electrophoresis ; charge transfer complexation ; argentation ; silver ion ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This study represents the first application of Ag(I) charge transfer complexation in nonaqueous capillary electrophoresis. This method applies the principles of argentation chromatography to nonaqueous electrophoretic separations and is termed “nonaqueous argentation electrophoresis”. Since the separations are performed in 100% nonaqueous media, the advantages of nonaqueous solvents, such as enhanced solubility and flexibility in selectivity enhancement, compared to an aqueous or mixed hydroorganic solvent, are realized. A variety of compounds were separated. Qualitatively, the separation of eleven sulfonamides in 100% acetonitrile is shown to improve greatly upon the addition of Ag(I). These results also show that nonaqueous argentation electrophoresis provides fast, well-resolved separations of compounds, such as N-containing heterocyclics, that can selectively complex with Ag(I). Migration data and separation selectivities of these compounds by nonaqueous argentation electrophoresis were compared to previous aqueous argentation electrophoresis results. Selectivities were found to be significantly different for the two separation media. Ag(I) complexation provides an effective means of manipulating selectivity in nonaqueous capillary electrophoresis.
    Additional Material: 9 Ill.
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  • 98
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    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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  • 99
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    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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  • 100
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    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.
    Type of Medium: Electronic Resource
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