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  • 1995-1999  (39)
  • 1980-1984
  • 1890-1899
  • 1995  (39)
  • Gas chromatography
  • 1
    Electronic Resource
    Electronic Resource
    Assessment of occupational exposure to 4,4′-methylenedianiline by the analysis of urine and blood samples (1995)
    Springer
    International archives of occupational and environmental health 67 (1995), S. 67-72 
    Details
    ISSN: 1432-1246
    Keywords: Dermal exposure ; Biological monitoring ; Gas chromatography ; Mass spectrometry ; Methylenedianiline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Seven workers at a work site where methylenedianiline (MDA) was used as a curing agent for an epoxy resin were studied during 4 workdays and one weekend. Internal exposure was monitored by analysis of 4,4′-MDA in hydrolysed urine and blood. After acidic hydrolysis, MDA was extracted, derivatised by use of pentafluoropropionic anhydride, and determined by gas chromatography and mass spectrometry, with negative ion chemical ionization. There was wide variation of MDA concentrations in hydrolysed blood between the workers (range 10–60 nmol/l). Also, the urinary excretion rate varied considerably both between and within the individual workers (0–90 μmol/h). The urinary excretion displayed some variation in relation to exposed periods. The urinary levels were linearly related to the concentrations in blood (r s= 0.93,P = 0.02). The present results show the value of excretion of MDA in hydrolysed urine and concentrations in blood as means for the biological monitoring of MDA exposure. In this case, the exposure was probably mainly dermal, in spite of extensive protection measures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00572228
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  • 2
    Electronic Resource
    Electronic Resource
    Rapid multiresidue screening method for organophosphate pesticides in vegetables (1995)
    Springer
    Chromatographia 40 (1995), S. 417-420 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organophosphate pesticides ; Vegetables ; Pesticide residue analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and efficient multiresidue extraction procedure using ethyl acetate and sodium sulfate has been applied to the analysis of diazinon, methamidophos, chlorpyrifos, malathion, parathion, parathion-methyl, dimethoate and monocrotophos residues in many different kinds of vegetables. No cleanup step was required Concentrated extracts were analysed by gas chromatography with flame photometric detection in phosphorus mode. Recovery studies were performed in six kinds of matrices at two fortification levels. Recoveries were in the range 80–115%. The limit of quantification of the analytical method has been estimated as 0.01 ppm for diazinon, methamidophos and malathion, 0.03 ppm for chlorpyrifos, parathion, parathion-methyl and dimethoate and 0.1 ppm for monocrotophos. Experiments showed that potentially it should be possible to develop a rapid and universally applicable method for organophosphate pesticide residues in different matrices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269905
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  • 3
    Electronic Resource
    Electronic Resource
    Relations between pneumatic parameters of ideal gas in a column with uniform permeability (1995)
    Springer
    Chromatographia 41 (1995), S. 15-22 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Average velocity of carrier gas ; Compressibility of carrier gas ; Pneumatic parameters of carrier gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This report was conceived as a source for the relations between five pneumatic parameters of carrier gas-inlet and outlet pressure, inlet and outlet velocity, and average velocity. Any pair of these parameters can be independent while the remaining three can be expressed as functions of the independent pair. As the total number of the independent pairs is ten, thirty different functions describing relations between arbitrary independent pairs and dependent parameters can be identified. All thirty were derived below together with the complete set of bounds for variations of independent parameters. To derive some relations, a third order rational equation had to be solved. Some properties of that solution are discussed. A simple case of vacuum operations with zero outlet pressure has also been considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274189
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  • 4
    Electronic Resource
    Electronic Resource
    Simulation of column efficiency in temperature programmed gas-liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 37-42 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Temperature programming ; Isothermal measurements ; Column efficiency ; Dead time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary If the dependence of HETP on temperature is specified under isothermal conditions, it is possible to predict the HETP for programmed temperature elution and subsequently peak width at half-height. This requires knowledge of isothermal retention time at retention temperature, which is computed by means of a model including the variation with temperature of dead time estimated from 3 homologs with carbon number: n, (n+j), (n+jk), where n, j and k are any integers. Predicted and measured peak widths corresponded within 4–9%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274193
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of pesticide residues in fruit and vegetables by matrix solid phase dispersion (MSPD) and different gas chromatography element-selective detectors (1995)
    Springer
    Chromatographia 41 (1995), S. 685-692 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Matrix solid phase dispersion (MSPD) ; Fruit and vegetables ; Pesticide residues ; Selective detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison between different element selective detectors for the determination of organophosphorus and organochlorine pesticide residues, from fruit and vegetables, was performed by capillary GC with electron capture detector (ECD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD) in the sulphur and phosphorus modes, and mass spectrometry detector (MSD) in selected ion monitoring (SIM) mode. Pesticides were extracted from the different foodstuffs by Matrix Solid Phase Dispersion (MSPD). Recoveries of 41–108 % with relative standard deviation of 2–14 % in the concentration range 0.5–10 μg L−1 were obtained in oranges, lemons, grapefruit, pears, plums, lettuces and tomatoes. The results demonstrated that the extracts of all the samples can be analyzed by the detectors used since no interfering co-extracted compounds were detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267805
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of correlation equations for the prediction of gas chromatographic separation of alkylbenzenes (1995)
    Springer
    Chromatographia 41 (1995), S. 183-186 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation equation ; Alkylbenezenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detailed statistical analysis, comparing the validity of the best literature recommended equations for prediction of retention indices of alkylbenzenes on squalane and methylsilicone stationary phases with the unified retention index concept, is presented. A comparison with literature sources shows that the unified retention index provides the smallest residual error. Hence, it can be applied for prediction purposes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267952
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  • 7
    Electronic Resource
    Electronic Resource
    Ring opening of cyclohexane over ZSM-zeolites followed by reversed-flow gas chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 227-235 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Catalysis ; Ring opening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Kinetic parameters for the ring opening of cyclohexane over modified ZSM-5 zeolites can be measured simultaneously under non-steady state conditions using reversed-flow gas chromatography. At relatively low temperatures, the main product detected and measured was propene. The mathematical relations used for the calculation of adsorption-desorption rate constants, surface reaction rate constants and adsorption equilibrium constants for the reactant cyclohexane are different from previously studied catalytic reactions, owing to the different experimental arrangement for feeding the catalytic bed. The diffusion bands obtained experimentally for reactant or product are described by the sum of two or three exponential functions of time, respectively. From the exponential coefficients of time and the pre-exponential factors, all determined by simple PC programs, the above kinetic parameters are calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267960
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  • 8
    Electronic Resource
    Electronic Resource
    The correlation equations describing retention index data on OV-101, OV-275 and PEG 20M.n-Alkanes andn-alkynes (1995)
    Springer
    Chromatographia 41 (1995), S. 726-727 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention indices ; Correlation equations ; n-Alkenes ; n-Alkynes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The correlation equations between Kovats retention indices ofn-alkenes andn-alkynes, column temperature and number of carbon atoms in molecules of these compounds on OV-101, OV-225 and PEG 20M capillary columns have been calculated. The two variable equationI=A+B·n+C/T give a good fit and are the simplest for prctical use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267812
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  • 9
    Electronic Resource
    Electronic Resource
    Quantitative determination of toxic mono- and non-ortho polychlorinated biphenyls in cod liver oil after selective liquid chromatographic separation (1995)
    Springer
    Chromatographia 41 (1995), S. 585-593 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Polychlorinated biphenyls ; Cod liver oil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary By application of a chromatographic column filled with Supelclean ENVI-Carb/Celite and elution with three solvents of different polarity three PCB fractions were obtained. Fraction A contained poly-ortho PCBs, Fraction B mono-ortho PCBs, and Fraction C non-ortho PCBs. The Supelclean ENVI-Carb/Celite column was used in combination with a sample preparation procedure for pre-cleaning of acid-stable chlorinated hydrocarbons such as DDT and its metabolites, HCH isomers, and regulation-relevant PCB congeners. The method was optimized using standard solutions of 55 PCB congeners, 8 chlorinated pesticides and contaminated cod liver oil samples. The influence of traces of remaining matrix on the elution profile of the organochlorine compounds on Supelclean ENVI-Carb/Celite was observed. Quantitation was carried out by GC-ECD with fused silica capillary columns of different polarity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269724
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  • 10
    Electronic Resource
    Electronic Resource
    Backbone modification of Chirasil-Val: Effect of nonpolar side chains on enantiomer separation in gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 718-723 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantiomer separation ; Chiral polysiloxane ; Amino acids ; Physicochemical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The polysiloxane backbone of the gas chromatography phase Chirasil-Val has been modified by replacing one methyl group per dialkylsiloxy unit by pentyl and hexyl groups, respectively. The new phases offer the advantage of reduced polarities and softening points, while the separation factors (α) of enantiomeric pairs of N,O-trifluoroacetyl amino acid propyl esters show small but intriguing deviations from those determined on Chirasil-Val.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02315143
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  • 11
    Electronic Resource
    Electronic Resource
    High temperature capillary GC analysis of phytopreparations of “espinheira santa” (Maytenus ilicifolia M. andMaytenus aquifolium M. — Celastraceae), a Brazilian antiulcer plant (1995)
    Springer
    Chromatographia 40 (1995), S. 341-344 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pentacyclic triterpenes ; Maytenus aquifolium Martius ; Maytenus ilicifolia Martius ; Phytopharmaceuticals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We report a method for the analysis of triterpenes in aqueous alcoholic extracts ofM. ilicifolia orM. aquifolium leaves, using high temperature capillary gas chromatography in polar columns (OV-17-OH). These species are popularly known in Brazil as “espinheira santa” and have proven antiulcer properties. The method consists of the pre-concentration of the triterpenes from the aqueous alcoholic extract, followed by GC analysis, which permits the determination of the presence of friedelan-3-ol and friedelin. Direct comparison with several triterpenol standards that are usually found in falsified “espinheira santa” samples but are absent in the authentic drug, showed that GC analysis clearly allows detection of the presence of friedelan-3-ol and friedelin and, therefore, permits distinguishing between authentic and false “espinheira santa” aqueous alcoholic extracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290367
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  • 12
    Electronic Resource
    Electronic Resource
    A gas chromatographic flow method for preconcentration and determination of vitamins D2 and D3 in pharmaceutical preparations (1995)
    Springer
    Chromatographia 40 (1995), S. 425-431 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Continuous preconcentration method ; Vitamins D2 and D3 ; Pharmaceutical preparations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A continuous-flow method that combines on-line preconcentration and isolation with gas chromatography for the direct determination of vitamins D2 and D3 in oily solutions is reported. A silica gel column permits preconcentration and isolation of analytes from the vitamin D matrix, although some triglyceride (ca. 25%) is also retained. To overcome problems associated with the low volatility of triglycerides, their retained fraction is further transesterified with potassium methylate to fatty acid methyl esters after elution. The proposed method was applied to the determination of vitamin D in pharmaceutical preparations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269907
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  • 13
    Electronic Resource
    Electronic Resource
    Correlations between gas chromatographic retention data of polycyclic aromatic hydrocarbons and several molecular descriptors (1995)
    Springer
    Chromatographia 40 (1995), S. 532-538 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention-structure correlation ; Molecular descriptors ; Polycyclic aromatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Statistical and factor analysis have been used to test the ability of several molecular descriptors to predict the retention indexes (I) of polycyclic aromatic hydrocarbons determined on SPB-5 and SPB-20 stationary phases. Regression analysis with both columns showed that linear regression with connectivity index and bending energy of the molecules as independent variables gave the best correlation coefficients. ΔI 20–5, considered to be a measure of the polar forces in retention, gave a good correlation with the van der Waals radii of the molecules, or strain, and bending energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290264
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  • 14
    Electronic Resource
    Electronic Resource
    Investigation of thermal and analytical properties of two nematic liquid crystals by gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 581-586 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid crystals ; Internal and external NO2 compounds ; Transition temperature ; Analytical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thermal and analytical properties of two liquid crystals containing internal [2-nitro, 3-methyl 4-(4-heptylbenzoyloxy) 4′-methylazobenzene] and external NO2 [2,3-dimethyl 4-(4-heptylbenzoyloxy) 4′-nitroazobenzene] have been investigated by gas chromatography. Transitions temperatures are determined by inverse gas chromatography using standard columns. Good agreement with values determined by differential scanning calorimetry are found. Analytical capabilities of the two liquid crystals are shown in glass capillary columns. Compared to examples in the literature, the crystals used separated different kinds of solutes. In addition, high molecular mass solutes were eluted at relatively low temperatures. Typical separations are observed for hydrocarbon positional isomers, aromatic hydrocarbons, geometric isomers, and volatile aroma compounds. Comparison between the performance of internal and external, NO2-liquid crystals is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290272
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  • 15
    Electronic Resource
    Electronic Resource
    Preparation and gas chromatographic characterisation of 3-bromo-4-(4-methylbenzyloxy)azobenzene stationary phase (1995)
    Springer
    Chromatographia 41 (1995), S. 697-701 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; New stationary phase ; Packed columns ; Specific retention volumes ; Activity coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of 3-bromo-4-(4-methylbenzyloxy)azobenzene (BMBOA) and its use as a stationary phase in packed columns are described. Chromatographic characteristics such as column efficiency, polarity (McReynolds constants) and operating temperature range were studied. Retention factors, specific retention volumes and activity coefficients for alcohols, esters, ketones, aromatic hydrocarbons andn-alkanes were determined. Phenols and 2,3, and 4-chlorobenzyl chlorides were separated on the new phase. Based on experimental data some assumptions were made on the possible types of intermolecular forces between solute and solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267807
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  • 16
    Electronic Resource
    Electronic Resource
    Utilization of Rohrschneider's concept and Tekler equation in linear temperature programmed GC. Precalculation of retention data (1995)
    Springer
    Chromatographia 40 (1995), S. 28-32 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Linear temperature programming ; Tekler-equation extension ; Retention index precalculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An extension of Rohrschneider's concept to the field of the linear temperature programmed gas liquid chromatography, is proposed, which is based on Antoine's equation for the temperature dependence of the reduction index of Takács et al. and Tekler. The new method presented in this paper, applied to retention data of two stationary phases of low polarity, PS-255 and OV-105, gives a new possibility of precalculating retention data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274603
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  • 17
    Electronic Resource
    Electronic Resource
    Analysis of short chain fatty acids from different intestinal samples by capillary gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 550-556 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Open tubular columns ; Short chain fatty acids ; Intestinal fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A capillary gas-liquid chromatography method for the analysis of free short chain fatty acids in intestinal samples was developed. Analytical results obtained with intestinal samples are influenced not only by high molecular mass matrix constituents but also by matrix components with a molecular weight smaller than 5000 daltons. To achieve a faithful transfer of SCFA into the chromatographic system it was important to avoid accumulation of involatile deposits on the surface of the inlet liner. Cleaning of the inlet linear lead to a significant weakening of matrix effects. The method described, using an Innowax column, is more effective, particularly with respect to precision and sensitivity, and is clearly superior to packed columns. The capillary is the column of choice for the separation of short fatty acids in samples from the small intestine and stomach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290267
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  • 18
    Electronic Resource
    Electronic Resource
    Fast headspace analysis with short microcapillary columns (1995)
    Springer
    Chromatographia 41 (1995), S. 419-423 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Microcapillary columns ; Short columns ; Volatile compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method of analysis using headspace gas chromatography with microcapillary columns is proposed. Small diameter (50 μm I.D.) fused-silica capillary columns with non-extractable SE-54 and PS-255 polysiloxane stationary phases were used for the analysis of low boiling organic compounds. The small diameter columns possess the usual very high efficiency so that the method can be employed for the headspace analysis of complex mixtures. The use of short microcolumns reduces the analysis times in comparison to conventional capillary columns. Good performances were obtained in the analysis of volatile compounds in some lemon essential oil, perfumes, and water samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02318616
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  • 19
    Electronic Resource
    Electronic Resource
    Large volume sample introduction using temperature programmable injectors: Implications of liner diameter (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 19-27 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Large volume injection ; PTV injectors ; PTV splitless injection ; PTV solvent split injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180106
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  • 20
    Electronic Resource
    Electronic Resource
    Characterization of silicones by direct-deposition GC/FT-IR (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 289-294 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Supercritical fluid chromatography ; FT-IR spectrometry ; Characterization ; Silicones ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Materials used in the manufacture of silicone breast prostheses were analyzed by supercritical fluid chromatography (SFC) and high temperature gas chromatography (GC) coupled with direct deposition FT-IR detection. The chromatographic resolution and deposition quality were found to be unsatisfactory for SFC/FT-IR; however, high temperature GC/FT-IR produced excellent results. The chromatograms and spectra obtained allowed for the identification of poly-dimethyl silicones and mono-, di-, and tri-diphenylsubstituted poly-dimethyl silicones. An automated method of baseline correction was developed that allowed functional group chromatograms due to molecules containing Si-phenyl bonds to be constructed without significant interference from Si-methyl bonds despite the fact that the Si-C stretching mode of Si-phenyl bands overlapped significantly with the strong bands due to Si-CH3 groups.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180505
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  • 21
    Electronic Resource
    Electronic Resource
    Analysis of fragrances in cosmetics by gas chromatography-mass spectrometry (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 653-658 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Mass spectrometry ; Fragrance analysis ; Cosmetics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A gas chromatographic (GC)-mass spectrometric (GC-MS) method has been developed for the routine analysis of 11 fragrance substances in cosmetics: cinnamic alcohol, cinnamic aldehyde, eugenol, hydroxy citronellal, α-amyl cinnamic aldehyde, geraniol, isoeugenol, coumarin, dihydrocoumarin, citronellal and citral. Methods for sample preparation of various types of cosmetic products, prior to GC analysis, have also been developed and proved to be rugged. Detection limits of all of target fragrance substances were approximately 1 ppm. Calibration curves of the target fragrance substances analyzed by GC were found to be linear in the investigated concentration range, 0.005% - 0.50%. The recoveries of the target fragrances from various types of cosmetic products were 80% - 116% and the relative standard deviations of the quantitative analysis of the target fragrance substances were within 5%.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240181008
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  • 22
    Electronic Resource
    Electronic Resource
    Gas chromatographic study of the thermal and analytical properties of a nematic luquid crystal and its cupric complex (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 304-308 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Nematic liquid crystal ; Cupric complex ; Transition temperatures ; Analytical performance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nematic compound N-4-(2′-(4″-dodecyloxybenzoyloxy)-4′-do-decyloxy)azobenzenyl-4-dodecyloxysalicylideneimine, known as LH, and its cupric complex, bis[N-4-(2′-(4″-dodecyloxybenzoyloxy)-4′-dodecyloxy)azobenzenyl-4-dodecyloxysalicylidene]iminato of copper (II), known as CuL2 have been used as stationary phases for gas chromatography. The thermal properties of LH and CuL2 have been determined with conventional metal columns, using n-alkanes as solute probes. Plots of In V0g against 1/T clearly show the temperature transitions of LH and CuL2. The analytical capabilities of the two stationary phases were established by use of 25 m glass capillary columns. Satisfactory separations were obtained for positional hydrocarbon and halocarbon isomers, aromatic and polyaromatic compounds, and volatile essential oil constitutents.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180508
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  • 23
    Electronic Resource
    Electronic Resource
    Analysis of monoterpenes from conifer needles using solid phase microextraction (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 587-592 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Headspace ; Solid phase microextraction ; Retention index ; Monoterpenes ; Pinus ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The applicability of solid phase microextraction (SPME) to the headspace analysis of monoterpene hydrocarbons from conifer needles was examined. To this end, the influences of fiber coating thickness, exposure time, and exposure temperature on the enrichment of the different monoterpene hydrocarbons were investigated. The distribution constants between polydimethylsiloxane fiber and gas phase at a given temperature were found to be very different. A relation is therefore derived to calculate the distribution constants of substances not available from their Kováts retention indices. A slightly different approach could be the use of so-called “relative distribution factors”, not considering the actual volume of fiber coating. In view of the different enrichment conditions in SPME as well as the general problems of headspace analysis, a comparison with a completely different method of sample preparation is presented. Furthermore, some applications of SPME to the analysis of monoterpenes from pine needles are given.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180915
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  • 24
    Electronic Resource
    Electronic Resource
    Floral volatiles fromClarkia breweri andC. concinna (Onagraceae): Recent evolution of floral scent and moth pollination (1995)
    Springer
    Plant systematics and evolution 194 (1995), S. 55-67 
    Details
    ISSN: 1615-6110
    Keywords: Onagraceae ; Clarkia ; Gas chromatography ; mass spectrometry ; monoterpenes ; benzyl esters ; floral fragrances ; intraspecific variation ; moth pollination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Clarkia breweri (Onagraceae) is the only species known in its genus to produce strong floral fragrance and to be pollinated by moths. We used gas chromatography-mass spectrometry (GC-MS) to identify 12 abundant compounds in the floral headspace from two inbred lines ofC. breweri. These volatiles are derived from two biochemical pathways, one producing acyclic monoterpenes and their oxides, the other leading from phenylalanine to benzoate and its derivatives. Linalool and linalool oxide (pyran form) were the most abundant monoterpenoids, while linalool oxide (furan form) was present at lower concentrations. Of the aromatic compounds detected, benzyl acetate was most abundant, whereas benzyl benzoate, eugenol, methyl salicylate, and vanillin were present as minor constituents in all floral samples. The two inbredC. breweri lines differed for the presence of the additional benzenoid compounds isoeugenol, methyleugenol, methylisoeugenol, and veratraldehyde. We also analyzed floral headspace fromC. concinna, the likely progenitor ofC. breweri, whose flowers are odorless to the human nose. Ten volatiles (mostly terpenoids) were detected at low concentrations, but only when headspace was collected from 20 or more flowers at a time. Trans-β-ocimene was the most abundant floral compound identified from this species. Our data are consistent with the hypothesized recent evolution of floral scent production and moth pollination inC. breweri.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983216
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  • 25
    Electronic Resource
    Electronic Resource
    Chromatographic determination of phosphine (PH3) and hydrogen sulfide (H2S) in the headspace of anaerobic bacterial enrichments using flame photometric detection (1995)
    Springer
    Chromatographia 40 (1995), S. 399-403 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Phosphine ; Flame photometric detection ; Anaerobic bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method is presented which distinguishes phosphine from hydrogen sulfide and other possible headspace gases of anaerobic microbial cultures. In anaerobic cultures spiked with phosphine, this gas is recovered in the liquid and gaseous phase down to 10 pg per ml of gas or liquid. No biogenically produced phosphine was found. Phosphine in amounts as small as 30 ng per 1 can be stored for several days in glass bottles covered with rubber septa, filled with nitrogen, in the presence or absence of water or of an anaerobic bacterial culture. Due to the selectivity of the detector and the retention characteristics of the porous layer open tubular polymer column alkanes, alkenes and organosulfur compounds routinely found in anaerobic bacterial headspaces do not interfere with the analytical quantification of phosphine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269902
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  • 26
    Electronic Resource
    Electronic Resource
    Gas chromatography on a self-associating component of a binary phase. Retention model by formal analogy with conductance of electrolytes in dilute solution (1995)
    Springer
    Chromatographia 41 (1995), S. 221-226 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Binary stationary phase ; Self-associating phase components ; Retention model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dependence of specific retention by a binary stationary phase in GC can be expressed as the sum of the products of the specific retention of the pure components times their respective volume fractions. In this study, however, one component has a site, which is not only mainly responsible for the selectivity, but also participates in strong self-association. This requires introduction of a concentration-dependent factor (μx) in the corresponding term of the equation correlating Vg mix x with x. In the GC resolution of N-trifluoroacetyl-amino acid isopropyl esters on a binary phase, N-lauroyl-L-amino t-butyl amide-squalane, data for the values of μx were obtained. Adapting a previously developed LC retention model to the above GC data, an equation was derived for the dependence of μx on the weight fraction (x) of the selector, namely μx=√1/x. This relationship permits calculation of retention volumes on the binary phase for a given x, as well as corresponding resolution coefficients of enantiomeric amino acid derivatives with generally excellent agreement with experiment. The chirality of the system is not relevant to application of the equation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267959
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  • 27
    Electronic Resource
    Electronic Resource
    Modelling of GC and HPLC separations of simazin and atrazin by Experimental Design methodology (1995)
    Springer
    Chromatographia 41 (1995), S. 553-560 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Experimental design ; Modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Experimental Design methodology allows the modelling and optimization of the chromatographic separation of similar pesticides (triazine family) by GC and HPLC. The GC separation of simazin and atrazin is well modelled by a first degree equation, involving injected volume, carrier gas pressure and rising oven temperature. The LC is modelled by a second degree equation, depending on injected volume, eluent flow and composition. These calculated models allow easy optimization of the separations, using isoresponse curves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269719
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  • 28
    Electronic Resource
    Electronic Resource
    A comparison of the critical parameters of some adsorbents employed in trapping and thermal desorption of organic pollutants (1995)
    Springer
    Chromatographia 41 (1995), S. 599-604 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organic volatile pollutants ; Adsorbents ; Breakthrough volumes ; Thermal desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison of some adsorbents, commonly used for trapping trace volatile organic pollutants followed by thermal desorption, is presented. The evaluation has been performed on 12 compounds representative of the main classes of organic substances. Breakthrough volumes and desorption recoveries have been measured. Every adsorbent gave good results for a range of compounds, but none were able to cover all the compounds examined. Thus, a multilayer trap utilising the best features of each adsorbent was introduced with very good results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269726
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  • 29
    Electronic Resource
    Electronic Resource
    Adrenal tissue in the male African catfish, Clarias gariepinus: localization and steroid hormone secretion (1995)
    Springer
    Cell & tissue research 280 (1995), S. 653-657 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Adrenals ; Morphology ; Steroids ; Gas chromatography ; Mass spectrometry ; Clarias gariepinus (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Interrenal-like tissue in male African catfish is localized in paired organs, situated retroperitoneally anterior of the kidney. Histological and enzyme-histochemical (3β-hydroxysteroid dehydrogenase) reactions were carried out on sections of these organs in order to localize steroid-producing cells. In vitro incubations were carried out to determine the steroidogenic capacity of the interrenal-like tissue. Twenty-one steroids could be identified and quantified in the incubation medium, by means of gas chromatography followed by mass spectrometry. Cortisol, 5α- and 5β-androstanedione and androstenedione together comprised about 80% of the total steroid content. In a previous study, twenty testicular steroids were detected in plasma after castration. In the present investigation we have shown that most of these steroids can be produced by the interrenal-like tissue, which thus can be considered as an extra-testicular source of gonadal steroids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318367
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  • 30
    Electronic Resource
    Electronic Resource
    On-line coupling of solid-phase extraction and gas chromatography with atomic emission detection for analysis of trace pollutants in aqueous samples (1995)
    Springer
    Chromatographia 40 (1995), S. 119-124 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Atomic emission detection ; Aqueous samples ; Solid-phase extraction ; Organophosphorus pesticides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An on-line, solid-phase extraction gas chromatography atomic-emission detection (SPE-GC-AED) system has been set up using an on-column interface to transfer 100 μl of desorbing solvent to the GC part of the system. Analytical characteristics such as recovery, precision and linearity of calibration plots were comparable with those of the off-line combination of SPE-GC-AED using organophosphorus pesticides as test compounds. The fully on-line set-up causes a marked improvement in detection because of the quantitative transfer of the analytes from the SPE module to the GC: detection limits are as low as 5–20 ng l−1 for the analysis of 10 ml raw and spiked surface water samples using the phosphorus channel. Detection levels can be further enhanced by processing up to 100 ml samples. The integrated analytical system is robust. The potential of the on-line set up has been demonstrated for the analysis of surface water and waste water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02272157
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  • 31
    Electronic Resource
    Electronic Resource
    Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography use of an anion-exchange membrane to remove an ion-pair reagent from the eluent (1995)
    Springer
    Chromatographia 40 (1995), S. 267-271 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; On-line coupling ; Ion-exchange membrane ; Ion-pair reagent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In order to enable the coupling of reversed-phase liquid chromatography (RPLC) with capillary gas chromatography (GC), the performance of an anion-exchange micromembrane device has been studied to remove the ion-pair reagent methanesulphonic acid from an acetonitrile/water LC eluent. The regenerant in the membrane was tetrabutylammonium hydroxide dissolved in acetonitrile/water, which effects an anion-exchange of methanesulphonate ions for regenerant hydroxide ions. The efficiency of the exchange process was found to be 99.9%. This enabled the direct introduction of the LC eluent, free of ions and with the proper acetonitrile/water ratio, into the GC. The applicability of the on-line LC-micromembrane-GC system has been illustrated for the potential drug eltoprazine, which is quantitatively recovered with a coefficient of variation for standard solutions of 3% at the 150 μg/ml analyte level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290356
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  • 32
    Electronic Resource
    Electronic Resource
    On-line automated sample preparation-capillary gas chromatography for the analysis of plasma samples (1995)
    Springer
    Chromatographia 40 (1995), S. 500-506 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; ASPEC ; Trazodone in plasma ; Method automation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An automated sample preparation module, (the automated sample preparation with extraction columns, ASPEC), was interfaced with a capillary gas chromatograph (GC) by means of an on-column interface. The system was optimised for the determination of the antidepressant trazodone in plasma. The clean-up of untreated plasma was carried out with disposable C18 cartridges, using several washing steps. The analyte was desorbed with methanol, the extract was diluted on-line with buffer and preconcentrated on a PLRP-S trapping column. The trapping column was dried by purging with nitrogen gas. Desorption (phase switching) of the trapping column was carried out with ethyl acetate which was introduced into a retention gap using partially concurrent solvent evaporation conditions. Trazodone was determined by GC with flame ionisation detection (FID). With a 1 ml sample, this resulted in a detection limit for trazodone in plasma of 3 ng/ml. The system showed good linearity and repeatability in the range 0.01–1 μg/ml, thus covering the range of pharmacokinetic/dynamic-to-therapeutic concentrations of trazodone in plasma. Preliminary results for benzodiazepines are promising. They indicate that the use of a selective detector such as the nitrogen/phosphorus detector, is to be recommended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290259
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  • 33
    Electronic Resource
    Electronic Resource
    A simple gas chromatographic method for the analysis of oxygenates in gasoline (1995)
    Springer
    Chromatographia 40 (1995), S. 607-610 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Packed column separations ; C1−C4 alcohols ; Ethers ; Gasoline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A number of oxygenated compounds such as C1−C4 alcohols, methyl tert-butyl ether (MTBE), and tertamyl methyl ether (TAME) are increasingly being used in gasoline as octane boosters and to reduce vehicular emissions. Monitoring of individual oxygenates in gasoline is important for quality control and regulatory purpose. Although, several analytical methods based on gas chromatography have been reported, a need was still felt to develop a simple and cost effective method of analysis. In this paper, a packed column gas chromatographic method is described for the analysis of C1−C4 alcohols, MTBE and TAME over a wide concentration range (2–20% V/V) in gasoline. The method involves determination of alcohols and ethers separately on two different columns. The alcohols are determined on a 20 ft column packed with poly(ethylene glycol) 400 as a stationary phase while the ethers are analysed on a 20 ft OPN-Poracil C column. The analysis of alcohols on poly(ethylene glycol) 400 column also provides data on aromatic components of gasoline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290276
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  • 34
    Electronic Resource
    Electronic Resource
    Determination of cholesterol in milk fat by gas chromatography with direct injection and sample saponification (1995)
    Springer
    Chromatographia 41 (1995), S. 23-28 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Cholesterol ; Direct injection ; Saponification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and direct gas chromatographic (GC) method for determining free cholesterol in milk fat using a capillary column and programmed-temperature vaporizerinjector was assayed. It was compared with other procedures involving saponification of fat, solvent extraction of unsaponifiable matter—with and without fractionation by thin-layer chromatography—and transformation of sterols into silyl derivatives prior to GC analysis. This paper proposes an alternative to other published procedures. Repeatability of the method was assessed and the coefficient of variation determined as 2.1%. The alternative saponification method exhibited comparable accuracy (coefficient of variation=1.8%). Recovery ranged from 99.1% to 105.6%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274190
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  • 35
    Electronic Resource
    Electronic Resource
    Specific interactions of n-donor adsorbates with N-benzoylthiourea-copper(II) complexes chemically bonded to silica supports (1995)
    Springer
    Chromatographia 41 (1995), S. 107-111 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Metal complex stationary phases ; Specific interactions ; N-benzoylthiourea groups
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Silica was modified with γ-aminopropyltriethoxylsilane, and then the amino group was converted into an N-benzoylthiourea compound. Treatment with anhydrous CuCl2 solution, gave a copper(II) complex on the surface. In order to estimate the ability of the complex to interact specifically with electron donors, a number of retention parameters were determined for three groups of compounds showing electron-donor properties: ketones, ethers and nitroalkanes. On the basis of the results, the effect of adsorbate structure on the strength of specific interactions was established. The packings studied may be useful for the analysis of the mixtures of ketones, ethers, and nitroalkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274203
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  • 36
    Electronic Resource
    Electronic Resource
    Solid phase microextraction using fused silica fibers coated with graphitized carbon black (1995)
    Springer
    Chromatographia 41 (1995), S. 678-684 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid phase micro extraction ; Graphitized carbon black ; Volatile organic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper presents the results obtained using fused-silica fibers coated with graphitized carbon black (Carbograph-Alltech) for solid-phase microextraction (SPME). The extraction and calibration curves relative to organic micro-pollutants present in gaseous and aqueous samples are reported. Examples of applications of this extraction procedure to GC and GC-MS analysis of organic micro-pollutants in actual samples are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267804
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  • 37
    Electronic Resource
    Electronic Resource
    Determination of volatiles in spirits using combined stationary phases in capillary GC (1995)
    Springer
    Chromatographia 41 (1995), S. 722-725 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Mixed stationary phases ; Distilled beverages ; Direct analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1∶1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267811
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  • 38
    Electronic Resource
    Electronic Resource
    Capillary gas chromatography of aromatic bicyclic and tricyclic spiro ketones (1995)
    Springer
    Chromatographia 41 (1995), S. 594-598 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Capillary column ; Bicyclic spiro ketones ; Tricyclic spiro ketones ; Retention index at different temperatures ; Retention vs stationary phase polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of some aromatic bicyclic and tricyclic spiro ketones on fused silica capillary columns coated with polydimethylsiloxane, cyanopropylmethylsiloxane and poly(ethylene glycol) stationary phases was investigated. Retention indices were determined at two temperatures in order to enable understanding of the compounds' chromatographic behaviour. The respective standard deviation values were 0.8, 0.5 and 0.3 index units. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic spiro ketones is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269725
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  • 39
    Electronic Resource
    Electronic Resource
    Adrenal tissue in the male African catfish, Clarias gariepinus: localization and steroid hormone secretion (1995)
    Springer
    Cell & tissue research 280 (1995), S. 653-657 
    Details
    ISSN: 1432-0878
    Keywords: Adrenals ; Morphology ; Steroids ; Gas chromatography ; Mass spectrometry ; Clarias gariepinus (Teleostei)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Interrenal-like tissue in male African catfish is localized in paired organs, situated retroperitoneally anterior of the kidney. Histological and enzyme-histochemical (3β-hydroxysteroid dehydrogenase) reactions were carried out on sections of these organs in order to localize steroid-producing cells. In vitro incubations were carried out to determine the steroidogenic capacity of the interrenal-like tissue. Twenty-one steroids could be identified and quantified in the incubation medium, by means of gas chromatography followed by mass spectrometry. Cortisol, 5α-and 5β-androstanedione and androstenedione together comprised about 80% of the total steroid content. In a previous study, twenty testicular steroids were detected in plasma after castration. In the present investigation we have shown that most of these steroids can be produced by the interrenal-like tissue, which thus can be considered as an extra-testicular source of gonadal steroids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318367
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