Direct Injection Gas Chromatography Research Articles

GC-MS determination of low hydrocarbon species (C 1–C 6) from a diesel partial oxidation reformer

The partial oxidation (PO x) reforming of Ultra Low Sulphur-Diesel (ULSD), rapeseed methyl ester (RME) - biodiesel and Fischer–Tropsch synthetic diesel fuels (SD) were studied by using a fixed-bed reactor. The ease of reforming the three fuels was first examined at different O/C feed ratios at constant gas hourly space velocity (GHSV) of 35 k h −1 over a prototype monolith catalyst (1%Rh/CeO 2–ZrO 2). The hydrocarbon species (C 1–C 6) produced in the reformer were analyzed using direct gas injection gas chromatography mass spectrometry (GC-MS). Under the same O/C ratios for 35 k h −1 the fuels conversion and process efficiency was dependent on the fuel type, and followed the general trend: SD > biodiesel > ULSD. The GC-MS analysis shows that both, biodiesel and ULSD diesel produced significantly higher amounts of alkenes compared to SD fuel. Fuel with relatively high aromatics content such diesel can be efficiently reformed to syngas over the catalyst used in this study but the reformer operating range (e.g. O/C ratio and space velocity) is limited compared to paraffinic fuels such as FT-SD. At increased GHSV of 45 k h −1 and O/C = 1.75, the diesel fuel conversion efficiency to syngas (H 2 and CO) was improved significantly and the formation of intermediate species such as methane, ethylene, and propylene was reduced considerably as a result of the increased peak reaction temperatures. The reduced HC species and increased H 2 concentration in the reactor product gas from the reforming of FT-SD fuel can provide significant advantages to the IC engine applications.

Metabolic footprinting as a tool for discriminating between brewing yeasts

The characterization of industrial yeast strains by examining their metabolic footprints (exometabolomes) was investigated and compared to genome-based discriminatory methods. A group of nine industrial brewing yeasts was studied by comparing their metabolic footprints, genetic fingerprints and comparative genomic hybridization profiles. Metabolic footprinting was carried out by both direct injection mass spectrometry (DIMS) and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS), with data analysed by principal components analysis (PCA) and canonical variates analysis (CVA). The genomic profiles of the nine yeasts were compared by PCR-restriction fragment length polymorphism (PCR-RFLP) analysis, genetic fingerprinting using amplified fragment length polymorphism (AFLP) analysis and microarray comparative genome hybridizations (CGH). Metabolomic and genomic analysis comparison of the nine brewing yeasts identified metabolomics as a powerful tool in separating genotypically and phenotypically similar strains. For some strains discrimination not achieved genomically was observed metabolomically.

Recent progress in the determination of volatile impurities in pharmaceuticals

We review and discuss recent developments and the main trends in the determination of volatile impurities in drugs, with literature references and applications. We present an overview of regulatory and pharmacopeial status and trends. The techniques described are direct injection, static headspace and solid-phase microextraction (SPME) gas chromatography (GC) together with some gravimetric and thermogravimetric applications. Relevant research provided solutions to all the main challenges in static headspace GC techniques. SPME was extensively used, mainly for identification purposes.

Rapid determination of short-chain fatty acids in colonic contents and faeces of humans and rats by acidified water-extraction and direct-injection gas chromatography

Short-chain fatty acids (SCFAs) have attracted much attention recently because of their positive physiological effects. In this work, a rapid and reliable gas chromatographic method for determination of eight SCFAs, in colonic and faecal samples from rats and humans has been developed and validated. The methodology involves extraction of the SCFAs in water before a direct injection procedure on a FFAP capillary column. A stock standard solution containing acetic acid, propionic acid, n-butyric acid, i-butyric acid, n-valeric acid, i-valeric acid, n-caproic acid and n-heptanoic acid was prepared and used. A high linearity (r2 > 0.9990), low quantification limit (2.38-30.14 microm) and high recovery for most acids were obtained. Acidification of faecal samples was found to be crucial for quantitative determination of the SCFAs, and adjustment of pH to 2-3 was regarded as necessary. Glass wool inserted in the glass liner of the injection port proved effective in preventing the contamination of the column by non-volatiles, and 12% formic acid reduced the ghost peak that appeared gradually after several injections. After validation, the methodology was applied on two faecal samples from rats fed diets containing different amount of dietary fibre and one faecal sample from human fed a normal diet to test the accuracy of the developed method.

Methyl methacrylate in poly(methyl methacrylate)—validation of direct injection gas chromatography

Gas chromatography (GC) was investigated for the determination of residual methyl methacrylate (MMA) in heat-processed poly(methyl methacrylate) (PMMA) denture base material emphasizing recovery and validation. Standard solutions of MMA and emulsion-polymerized PMMA in dichloromethane were analysed, before and after distillation by a room-temperature air stream into a liquid nitrogen trap, and in the presence of PMMA by direct injection. Quantitative NMR analysis using dimethyl sulphoxide as internal calibration standard in deuterated chloroform solutions provided validation. Good concordance was observed between results under all conditions; no problems arose from direct injection of PMMA solution for GC. Good straight line responses in log–log plots were generally observed. For GC and MMA: log–log calibration curve (slope: 0.9552 ± 0.0051, r 2: 0.9992, n = 32) indicated some non-linearity ( t = 8.875, p ∼4 × 10 −10). Distillation gave slope: 0.9751 ± 0.0213 (NS versus unity; t = 1.172, p > 0.25). For PMMA solutions, distillation ( r 2: 0.9301) gave greater scatter than direct injection ( r 2: 0.9704). For NMR: log–log plot of calculated versus actual MMA (slope: 0.9363 ± 0.0157, r 2: 0.9969, n = 13) again indicated non-linearity ( t = 4.0682, p = 0.0019). PMMA solutions gave slope: 0.9477 ± 0.0328, r 2 = 0.9858 (NS versus unity; t = 1.5941, p = 0.13). Determination of MMA in PMMA by GC is recommended.

Analyses of orange spirit flavour by direct‐injection gas chromatography–mass spectrometry and headspace solid‐phase microextraction/GC–MC

AbstractOrange spirit, a novel fruit distillate, was analysed by direct injection gas chromatography–mass spectrometry and headspace solid‐phase microextraction (SPME) coupled to GC–MS. Different commercial SPME fibre types have been tested for the analysis of orange spirit. The divinylbenzene/carboxen on poly(dimethylsiloxane) fibre was chosen because it gave the best repeatability of the method. Headspace SPME–GC–MS selectivity was found to be comparable to GC direct injection for most orange spirit volatile compounds. The divinylbenzene/carboxen/poly(dimethylsiloxane) fibre had very high affinity for non‐polar and less polar compounds, especially for some components of orange peel oil, which could be considered the impact compounds of orange spirit. In this way, good sensitiveness was ensured for these compounds. Conversely, the GC analysis was more sensitive for polar compounds, especially for molecules such as methanol, isobutanol, n‐butanol and iso‐amyl alcohols. SPME was a useful tool for quickly screening orange flavour compounds and can be considered as complementary to GC direct injection analysis, which should be used when an accurate quantitative determination of analytes is required. Copyright © 2002 John Wiley & Sons, Ltd.

Theoretical principles of thin layer headspace analysis

Theoretical principles of thin layer headspace (TLHS) analysis are reviewed. TLHS utilizes a special heated column in which a continuously flowing thin film of a liquid sample is contacted with a continuously flowing pure gas. Volatile analytes contained in the liquid sample pass to the gas phase and are carried away from the column. For the determination of volatile organic halogen (VOX), the analytes in the gas are mineralized at 900°C, and the mineralization products (hydrogen halides) are absorbed in an appropriate solvent in a second TLHS column kept at ambient or sub‐ambient temperature. The mineralization products can be quantified in the liquid sorbent using conductometric, spectrophotometric, as well as direct and indirect potentiometric methods. The unique feature of this method is the dynamic preconcentration of the analyte in the liquid sorbent. When analyte speciation is required, the liquid sorbent can be generated in TLHS column II by condensation of the water vapour carried by the gas from TLHS column I, and the condensed phase can be analyzed by direct liquid injection gas chromatography. General equations describing the recovery of the analyte or its conversion products in TLHS column II are given, followed by general and partial solutions yielding insight into the nature of the processes and being useful for optimization of the operating parameters of the method. Conditions under which TLHS analysis can be used to separate two compounds are discussed.

Comparative Evaluation of Four Methods for Assay ofcis-andtrans-Resveratrol

A comparative evaluation of four methods to measure the concentrations of <i>cis-</i> and <i>trans-</i>resveratrol as well as total resveratrol in commercial wines has been performed. Two of these methods utilized solid-phase extraction of resveratrol isomers prior to analysis by direct-injection gas-chromatography mass-spectrometry (GC-MS) or derivatization with <i>bis</i>-[trimethylsilyl]-trifluoroacetamide (BSTFA) prior to GC-MS analysis. Two methods utilized direct-injection high performance liquid chromatography (HPLC) in normal phase (isocratic) with absorbance detection at 306 nm, and reverse phase HPLC with gradient elution and diode array detection. In virtually all comparisons, the correlation between the values for any two methods was very satisfactory (r &gt; 0.900), but some evidence of systematic bias was obtained which could not be explained by different standardization techniques. High values for <i>trans-</i>resveratrol with direct-injection GC-MS (Method 1) could be attributed, at least in part, to thermal breakdown of resveratrol glucosides to free isomers. The derivatization GC-MS technique (Method 2) showed a tendency to overestimate <i>cis-</i>resveratrol and underes- timate the trans isomer, possibly as a consequence of <i>trans-</i> to-<i>cis</i> isomerization during the derivatization step. Somewhat lower values for <i>cis-</i>resveratrol with the normal-phase HPLC procedure (Method 3) might be a consequence of monitoring a single wavelength (306 nm) which is well above the absorption maximum of this isomer. Method 4 (reverse-phase gradient HPLC with diode array detection) has the advantage of allowing the simultaneous quantitation of many other polyphenols of biologic interest, and as of now may be considered to be the most robust method for routine application.

Indoor exposure to perchloroethylene (PCE) in individuals living with dry-cleaning workers

Perchloroethylene (PCE) is the most widely used solvent in dry-cleaning; it is toxic to the liver, kidney and central nervous system and may be a human carcinogen. PCE levels in the ambient air of dry-cleaners' homes were measured, and samples of end-exhaled air (alveolar air) from subjects who were not themselves occupationally exposed, but who were members of the household of dry-cleaners were compared with samples from the general population. Thirty apartments were visited housing dry-cleaners and their families, and located well away from the dry-cleaning premises. Indoor air samples and alveolar air samples were collected contemporaneously from the dry-cleaners (36) and members of their household (34). The same sampling procedure was followed in 25 private homes where samples of alveolar air were collected from 41 subjects who were not occupationally exposed and who acted as control group. All the samples were analysed by direct-injection gas-chromatography. PCE levels in dry-cleaners' homes proved to be significantly higher than in control houses (geometric means: 265 vs. 2 μg/m 3, P < 0.001). PCE levels in the alveolar air exhaled by dry-cleaners, their family members and control subjects were statistically different (geometric means: 5140, 225 and 3 μg/m 3, respectively; P < 0.001). PCE is a ubiquitous substance in indoor air, but is present at higher concentrations in apartments where dry-cleaners and their families live. Biological monitoring of PCE in alveolar air confirms that family members of dry-cleaners are more exposed than the general population.

Transport and intracellular accumulation of acetaldehyde in saccharomyces cerevisiae

The rate of acetaldehyde efflux from yeast cells and its intracellular concentration were studied in the light of recent suggestions that acetaldehyde inhibition may be an important factor in yeast ethanol fermentations. When the medium surrounding cells containing ethanol and acetaldehyde was suddenly diluted, the rate of efflux of acetaldehyde was slow relative to the rate of ethanol efflux, suggesting that acetaldehyde, unlike ethanol, may accumulate intracellularly. Intracellular acetaldehyde concentrations were measured during high cell density fermentations, using direct injection gas chromatography to avoid the need to concentrate or disrupt the cells. Intracellular acetaldehyde concentrations substantially exceeded the extracellular concentrations throughout fermentation and were generally much higher than the acetaldehyde concentrations normally recorded in the culture broth in ethanol fermentations. The technique used was sensitive to the time taken to cool and freeze the samples. Measured intracellular acetaldehyde concentrations fell rapidly as the time taken to freeze the suspensions was extended beyond 2 s. The results add weight to recent claims that acetaldehyde toxicity is responsible for some of the effects previously ascribed to ethanol in alcohol fermentations, especially Zymomonas fermentations. Further work is required to confirm the importance of acetaldehyde toxicity under other culture conditions.

Comparison of Plasma, Serum, and Whole Blood Ethanol Concentrations

The differences in ethanol concentrations, as measured by direct injection gas chromatography, among plasma, serum, and whole blood from living human subjects are examined. The samples containing serum and the corresponding ones containing whole blood arrived at the laboratory as part of the same submission. The ratio of the concentration of ethanol in serum to that in plasma is 1.00 +/- 0.01:1 with a range of 0.98:1 to 1.04:1. The serum/whole blood ratio and plasma/whole blood ratio are both 1.12 +/- 0.02:1. The former has a range of 1.09:1 to 1.18:1 and the latter ranges from 1.09:1 to 1.17:1.

Quantitative analysis of orange juice flavor volatiles by direct-injection gas chromatography

Quantitative analysis of orange juice flavor volatiles by direct-injection gas chromatography

Direct injection technique for gas chromatographic determination of ethanol and other volatiles in concentrated cell suspensions

The accuracy of direct injection gas chromatography for the estimation of volatile components in concentrated, undisrupted cell suspensions was assessed. Quantitative recovery of intracellular and extracellular ethanol, butanol and acetone was obtained. The technique eliminates the requirement for a separate disruption step to release intracellular components and the need to measure the percentage of disrupted cells.

Reactions of singlet oxygen in humic waters

SUMMARY. The oxidation of 2, 5‐diniethylfuran (DMF) to cis‐1, 2‐ diacetylethylene (DAE) is a specific test for singlet oxygen (1O2). A method has been developed for the measurement of DAB by direct injection gas chromatography. By the use of this method, the photochemical generation of 1O2 has been demonstrated in samples of two Canadian humic waters.Two other photochemical reactions probably mediated by 1O2generation, the oxidation of histidine and the inactivation of a‐chymotrypsin, have been demonstrated in these waters.The possible ecological and environmental implications of these findings are discussed.

The determination of traces of organohalogen compounds in aqueous solution by direct injection gas chromatography—mass spectrometry and single ion detection

By means of gas chromatography—mass spectrometry with direct injection, a diglycerol column and single ion detection, a detection limit of 2 μg l -1 can be obtained for chloroform and other organohalogen compounds in aqueous solutions: no concentration or extraction is required.

Concentration of solutes from aqueous solution

Various methods for the concentration and determination of organic substances in drinking water are discussed. In each case, a reference for the method is given; the method is discussed briefly; and the accuracy or precision and applicablity of the method are mentioned. Methods discussed are resin sorption, solvent extraction, gas stripping, water-gas distribution, direct injection gas chromatography, resin sorption-pyridine desorption, and resin sorption-thermal desorption. (BLM)

The Determination of Solvation Numbers of Ligands, Chelates, and Complexes in Various Solvents by Differential Direct Injection Enthalpimetry, Viscosity, and Gas Chromatography Measurements

Abstract The number of H2O and organic solvent molecules associated with rhodo-mine B, tris-1,10-phenanthroline iron(II) chloride, and iron(III) ace-tylacetonate in seven extraction solvent systems was determined. The methods of measurement were viscosity, gas chromatography, and differential direct injection enthalpimetry.

Stability of Preservatives (I)

The degradation mode of sorbic acid, dehydroacetic acid, methyl- and propyl-p-hydroxybenzoate in aqueous solution respectively was studied, using gas chromatographic assay method. It was noted that sorbic acid both in acidic and alkaline region was the most stable of these preservatives, whereas dehydroacetic acid was rapidly decomposed either in acidic or in strong alkaline and, hydrolysis of p-hydroxybenzoate was observed in alkaline region.The simultaneous detection of 2, 6-dimethyl-4-pyrone, 2, 6-dimethyl-4-pyrone-3-carboxylic acid, triacetic acid lactone and 2, 6-dihydroxy-2, 5-heptadien-4-one (diacetylacetone) as presumable degradation products of dehydroacetic acid could be readily implemented with direct injection gas chromatography.The degradation mechanisms of dehydroacetic acid and 2, 6-dimethyl-4-pyrone-3-carboxylic acid, both in acidic solution at 60° respectively, were followed by gas chromatography at a given time interval. As degradation products of dehydroacetic acid and 2, 6-dimethyl-4-pyrone-3-carboxylic acid, 2, 6-dihydroxy-2, 5-heptadien-4-one (diacetylacetone) and 2, 6-dimethyl-4-pyrone were identified with direct injection gas chromatography, and 3-carboxy-2, 6-dihydroxy-2, 5-heptadien-4-one was separable newly as the ester.According to the degradation products, the degradation pathway of dehydroacetic acid in acidic solution was considered to be the fact that of the lactone ring dehydroacetic acid was first broken to produce 3-carboxy-2, 6-dihydroxy-2, 5-heptadien-4-one, and then its decarboxylation immediately following the reaction yielded 2, 6-dihydroxy-2, 5-heptadien-4-one, which was dehydrated finally to 2, 6-dimethyl-4-pyrone.