Chiral High-resolution Gas Research Articles

Simple gas chromatographic method for the stereodifferentiation of methyl nilate, a chiral α-methyl-β-hydroxy ester

The four stereoisomers of methyl nilate, methyl 3-hydroxy-2-methylbutanoate, have been separated and analyzed by the direct simultaneous achiral-chiral high-resolution gas chromatography (HRGC) and also by the chiral high-resolution gas chromatography-time-of-flight mass spectrometry (HRGC-TOF-MS). The method involved the use of DB-5 and CP Chirasil-Dex CB columns. The elution sequences on the two columns were determined and are reported. The one-step GC method allows the identification by retention data and simultaneously to determine unequivocally the absolute configuration of nilic acid moieties contained in minor complex natural products without previous isolation, as part of a general strategy for the structure determination of the compounds.

Ultrasonic extraction followed by sulfuric acid silica gel cleanup for the determination of ?-hexachlorocyclohexane enantiomers in biota samples

Interest in the analysis of alpha-hexachlorocyclohexane (alpha-HCH) enantiomers as an alternative or complementary approach to elucidating isomer ratios of alpha/gamma-HCH has grown in recent years because it can provide useful information to evaluate the influence of different degradation and transformation processes. In this paper, a simple and rapid method for the determination of alpha-HCH enantiomers in biota samples is described. The method developed consists of ultrasonic extraction, sulfuric acid silica gel cleanup, solid-phase extraction (SPE) column fractionation, and final determination with chiral high-resolution gas chromatography. Ultrasonic extraction greatly shortens the extraction process time, and the sulfuric acid silica gel and SPE cleanup perfectly remove lipids and other interference compounds in the lipid-rich samples. The method is found to be simple, less time-consuming, and easy to operate, thus providing a useful alternative method to assess the enantioselective breakdown of alpha-HCH in biota system.

Selectivity tuning in chiral dual column gas chromatography.

The enantioselective tuning of two columns coupled in series is investigated in chiral high-resolution gas chromatography. Two columns with opposite enantioselectivities (Chirasil-L-Val and Chirasil-D-Val) are coupled in series via a T connector, and the relative retention of enantiomers chromatographed on the system is changed by varying the individual carrier gas flow rates in the coupled columns. The flow-rate ratio necessary for the required selectivity is calculated on the basis of the measured retention factors on the individual columns. The performance of this method for adjusting selectivity is studied by the separation of enantiomers of the N-TFA-O-methyl esters of six amino acids. It is demonstrated that the change of the coupling point carrier gas pressure, at the constant inlet and outlet pressures, may change the enantioselectivity of the given column series to such an extent that the enantiomer elution order may be reversed.

Isolation and identification of the metolachlor stereoisomers using high-performance liquid chromatography, polarimetric measurements, and enantioselective gas chromatography.

Because of the presence of two chiral elements (an asymmetrically substituted carbon and a chiral axis), the herbicide metolachlor consists of four stereoisomers stable at ambient temperature with aSS-, aRS-, aSR-, and aRR-configurations (aSS, the isomer with aS,1'S-configuration, etc.). Metolachlor, initially introduced into the market as the racemic product containing all four stereoisomers, is currently being replaced worldwide by S-metolachlor, the product enantiomerically enriched with the herbicidally active 1'S-isomers (aSS, aRS). The isomer-specific analysis of metolachlor requires not only enantioselective ("chiral") analytical techniques but also suitable reference compounds. In this study, two of the four metolachlor isomers were isolated from rac-metolachlor in enantio- (ee > 98%) and diastereomerically pure forms by a combination of achiral and chiral high-performance liquid chromatography (HPLC). The two isomers were identified as the aSS- and the aRR-isomers by polarimetric measurements, in reference to previous data. The two isomers were then thermally equilibrated to 1:1 mixtures of the aSS/aRS and aRR/aSR diastereomers, respectively, so that analytical data of all four metolachlor isomers became available; they were then used to identify these isomers in technical products by chiral high-resolution gas chromatography (HRGC). The kinetics of the thermally induced interconversion of the atropisomers was studied and the consequences, such as for GC analysis, are discussed. A comparison of on-column and split/splitless injection indicated that the latter technique results in significant isomerization prior to separation and, therefore, cannot be used for accurate isomer analysis.

Environmental Behavior of Acetamide Pesticide Stereoisomers. 2. Stereo- and Enantioselective Degradation in Sewage Sludge and Soil

The degradation of five acetamide pesticides (alachlor, acetochlor, metalaxyl, metolachlor and dimethenamid) with different types of stereoisomerism (axial- and/or C-chirality) was studied in soil and sewage sludge using chiral high-resolution gas chromatography/mass spectrometry (HRGC/MS). Overall degradation rates in both media were in the order of alachlor > acetochlor > dimethenamid > metolachlor > metalaxyl. The results indicated the degradation of metalaxyl, metolachlor, and dimethenamid to be stereo- and/or enantioselective, particularily with respect to C-chirality. For acetochlor (axial-chiral), the results were inconclusive due to interference in the detection of this compound. Metalaxyl showed different enantioselectivity in the two media with the 1'S-(+)-enantiomer faster degraded in sewage sludge and the fungicidal more active 1'R-(-)-enantiomer faster degraded in soil. α-Hexachlorocyclohexane (α-HCH) and its enantioselective degradation were used as an internal control to confirm biotic action in the sewage sludge. Surface water (lakes, drainage canal) and rain contained detectable quantities (2-120 ng/L) of some of these pesticides. The peak area ratios in all but one sample (drainage canal) were close to those of the technical products, indicating little if any biological degradation.

Isomer-selective and enantiomer-selective determination of DDT and related compounds using chiral high-resolution gas chromatography/mass spectrometry and chiral HPLC.

The composition of technical DDT was investigated using achiral and chiral high-resolution gas chromatography (HRGC) and electron-ionization mass spectrometry (EI-MS). 2,4'-DDT and 2,4'-DDD, two important components of technical DDT, were enantiomerically resolved by chiral HRGC with silylated β-cyclodextrin and by chiral high-performance chromatography (HPLC) with permethylated γ-cyclodextrin as chiral selectors. The (+)- and (-)-enantiomers were assigned by chiral HPLC using chiroptical measurements. Enantiopure isolates were then used to identity these enantiomers in chiral HRGC analyses. Previous data indicated (+)- and (-)-2,4'-DDT to have Sand R-configuration, respectively, but the absolute configurations for (+)- and (-)-2,4'-DDD were hitherto unknown. They were now assigned via the reductive dechlorination of the individual 2,4'-DDT enantiomers which proceeded stereoselectively to the corresponding 2,4'-DDD enantiomers. The results showed (+)- and (-)-2,4'-DDD to have R- and S-configuration, respectively. The enantiomers of 2,4'-DDD thus have reversed signs of rotation for polarized light compared to the enantiomers of 2,4'-DDT with the same configuration. The enantiomer resolution of several additional chiral compounds in technical DDT is reported ; enantiomeric ratios of 1.0 indicated all chiral compounds to be present as racemates in the technical and in the synthetic reference materials. We report the first enantioselective determinations of technical DDT ; the methods presented should also be applicable to the analysis of environmental and biological samples.

Environmental behavior of acetamide pesticide stereoisomers. 1. Stereo- and enantioselective determination using chiral high-resolution gas chromatography and chiral HPLC.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnvironmental behavior of acetamide pesticide stereoisomers. 1. Stereo- and enantioselective determination using chiral high-resolution gas chromatography and chiral HPLC.Hans-Rudolf. Buser and Markus D. MuellerCite this: Environ. Sci. Technol. 1995, 29, 8, 2023–2030Publication Date (Print):August 1, 1995Publication History Published online1 May 2002Published inissue 1 August 1995https://doi.org/10.1021/es00008a022RIGHTS & PERMISSIONSArticle Views392Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (929 KB) Get e-Alerts Get e-Alerts

Isomer and Enantioselective Degradation of Hexachlorocyclohexane Isomers in Sewage Sludge under Anaerobic Conditions

The degradation of the four most common hexachlorocyclohexane (HCH) isomers in sewage sludge was studied using chiral high-resolution gas chromatography/mass spectrometry. Pure isomers and the technical HCH mixture were incubated with sludge from a communal sewage sludge treatment plant. High enantioselectivity was observed for α-HCH with the (+)-enantiomer faster degraded than the (-)-enantiomer. The degradation rates of the different HCHs were in the order of γ-HCH > α-HCH > δ-HCH > β-HCH with half-lives between 20 and 178 h for y- and β-HCH, respectively. The rates correlate with the number of axial Cl's in an isomer. Degradation in active sewage sludge was predominantly biotic (80-95%), as compared to the slower degradation in sterilized sludge. However, degradation in sterilized sludge was still significantly faster than hydrolysis in water. This enhanced chemical degradation must be due to additional compounds present in sludge and may possibly involve surface-catalyzed reactions. Suspected initial metabolites of HCHs such as tetra- and pentachlorocyclohexenes (TCCHs, PCCHs) and -hexanes were not detectable, presumably because these compounds degrade even faster than they are formed. Despite the faster degradation of(+)-α-HCH under anaerobic conditions and its faster degradation in surface waters (North Sea, Baltic Sea, Canadian freshwater lakes) under aerobic conditions, (+)-α-HCH is more accumulating in most aquatic biota. General conclusions on the fate of chiral compounds in the environment and on consequences for the monitoring of such compounds using enantio- and nonenantioselective analyses are given.

Recognition of vinification technology through gas chromatographic data on enantiomeric purity of free amino acids

Analysis of D-amino acids in food, a matter of growing interest due to nutritional implications, has been used as a tool for food evaluation, detection of falsifications and as a genuinity parameter. The evolution of free D-amino acids in wines of a portuguese Vitis vinifera variety (Roupeiro white), bottled during the period 1978–1989 is studied by means of chiral high resolution gas chromatography. D-Ala, D-Val, D-Thr, D-Leu, D-Ser, D-Asx, D-Met, D-Phe, and D-Glx are present in most of the analyzed wines. It was not possible to correlate the evolution of the D/L ratio to the age of the wine. However, a clear correlation between enantiomer purity profiles and the vinification technique could be established. The results show that free D-amino acids may be used as markers for the biotechnological process used in vinification.

Transformation experiments with two chiral endosulfan metabolites by soil microorganisms ? CHIRAL HRGC on lipophilic cyclodextrin derivatives

Two chiral metabolites of the hexachlorinated cyclodien insecticide endosulfan, C9H6Cl6O3S, the endosulfan hydroxyether and the endosulfan lactone, were separated into their enantiomers using lipophilic β-cyclodextrin derivatives in chiral high-resolution gas chromatography (CHRGC). We separated the hydroxyether on heptakis-(2,3,6-tri-O-pentyl)-β-cyclodextrin (LIPODEX-C) and the endosulfan lactone on heptakis-(3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin (LIPODEX-D). We also investigated the enantioselective formation and transformation of these two metabolites by soil organisms. To approximate real world conditions of microbiological transformation, incubation experiments with mixed cultures of soil microorganisms were carried out. Significant differences were observed in the transformation experiments under aerobic and anaerobic conditions. The endosulfan hydroxyether (ESH) is not formed enantioselectively from prochiral endosulfan diol (ESD) in the aerobic transformation pathway. The hydroxyether itself is enantioselectively converted to the endosulfan lactone (ESL) as a major pathway only under aerobic conditions. Corresponding enantiomers of endosulfan hydroxyether and endosulfan lactone with the same absolute configuration could be assigned. The lactone enantiomers are stereoselectively formed via the hydroxyether as a minor pathway under anaerobic conditions. While the first eluting lactone enantiomer was more abundant in the aerobic experiment, it was the second eluting under anaerobic conditions. Four major so far unidentified metabolites were detected in the anaerobic incubations of both the endosulfan hydroxyether and the endosulfan diol.

Identification of the (+)- and (-)-Enantiomers of Chiral Chlordane Compounds Using Chiral High-Performance Liquid Chromatography/Chiroptical Detection and Chiral High-Resolution Gas Chromatography/Mass Spectrometry

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIdentification of the (+)- and (-)-Enantiomers of Chiral Chlordane Compounds Using Chiral High-Performance Liquid Chromatography/Chiroptical Detection and Chiral High-Resolution Gas Chromatography/Mass SpectrometryMarkus D. Mueller and Hans-Rudolf. BuserCite this: Anal. Chem. 1994, 66, 13, 2155–2162Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/ac00085a034RIGHTS & PERMISSIONSArticle Views237Altmetric-Citations37LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (862 KB) Get e-Alerts Get e-Alerts

Isomeric and Enantiomeric Composition of Different Commercial Toxaphenes and of Chlorination Products of (+)- and (-)-Camphenes

The isomeric composition of commercial toxaphenes, including products of U.S. and former Est German origin, and the enantiomeric composition of several key components were investigated using achiral and chiral high-resolution gas chromatography (HRGC) in combination with mass spectrometry (MS). Achiral HRGC with electron-capture, negative ionization (ECNI) MS was used for congener group analysis and chiral HRGC with electron ionization (EI) MS/MS for the isomer selective and enantioselective determination of some polychlorobornanes and polychlorobornenes [...]

Isomer- and enantiomer-selective analyses of toxaphene components using chiral high-resolution gas chromatography and detection by mass spectrometry/mass spectrometry

Achiral and chiral high-resolution gas chromatography (HRGC) in combination with electron ionization (EI) mass spectrometry/mass spectrometry (MS/MS) was used for the analysis of toxaphene components in a technical mixture and in tissue extracts of several aquatic vertebrate species collected from the Baltic Sea (herring, salmon, seal), the Arctic (seal), and the Antarctic (penguin). Enhanced isomer selectivity of some toxaphene components was obtained by selected-reaction monitoring (SRM) using ion transitions commonly not observed with other halogenated contaminants. All species showed extensive alteration of the original toxaphene mixture with only a few, but largely the same, polychlorobornanes present

Species discrimination in five species of winter-flying geometrids (Lepidoptera) based on chirality of semiochemicals and flight season

Enantiomer separation of (6Z,9Z)-cis-3,4-epoxynonadecadiene and (3Z,9Z)-cis-6,7-epoxynonadecadiene could be achieved using chiral high-resolution gas chromatography and a cyclodextrin-bond column. (3Z,9Z)-(6R,7S)-Epoxynonadecadiene was identified from ovipositor extracts ofColotois pen-Naria, while inErannis defoliaria the 6S,7R-enantiomer was found. In field trapping tests pure synthetic enantiomers caught only conspecific males of these species. (3Z,6Z,9Z)-Nonadecatriene was found in both species, while the presence of (3Z,6Z,9Z)-heneicosatriene was indicated inC. Pennaria only. A 10∶10∶3 blend of (3Z,9Z)-(6R,7S)-epoxynonadecadiene, (3Z,6Z,9Z)-heneicosatriene, and (3Z,6Z,9Z)-nonadecatriene was found to be optimal for catchingC. Pennaria, whileE. Defoliaria males were optimally caught by a 1∶1 mixture of (3Z,9Z)-(6S,7R)-epoxynonadecadiene and (3Z,6Z,9Z)-nona-decatriene. (6Z,9Z)-(3S,4R)-Epoxynonadecadiene was identified from ovipositor extracts ofAgriopis (Erannis) aurantiaria. In field tests the pure enantiomer proved to be a highly specific sex attractant for both the late autumn/early winter flyingA. Aurantiaria and the late winter/early spring flyingA. Leucophearia. Males ofAgriopis marginaria, which fly in late winter/early spring, were attracted to (3Z,9Z)-(6S,7R)-epoxynonadecadiene. The addition of (3Z,6Z,9Z)-nonadecatriene to theS,R-enantiomer increased captures. Optimal catches were recorded with a 10∶3 epoxide-hydrocarbon blend. Enantiomer specificity in all species was confirmed in EAG measurements.

Enantioselective determination of chlordane components, metabolites, and photoconversion products in environmental samples using chiral high-resolution gas chromatography and mass spectrometry

Enantiomer separation of various chlordane compounds, including heptachlor, the oxygenated metabolites heptachlor epoxide (HEP) and oxychlordane (OXY), and photoconversion products was investigated using chiral high-resolution gas chromatography and detection by electron ionization (EI) and electron-capture, negative ionization (ECNI) mass spectrometry (MS). In technical chlordane and in ambient air from Scandinavia, heptachlor and the chiral octa- and nonachlordanes were present in enantiomeric ratios of 1:1. The results indicate input of these compounds via aerial transport into the northern environment as racemic mixtures. Laboratory experiments using solid-phase photolysis by natural sunlight yielded caged and half-caged products from heptachlor and cis-chlordane, respectively.

Enantiomer separation of chlordane components and metabolites using chiral high-resolution gas chromatography and detection by mass spectrometric techniques

Octa- and nonachlordanes, oxychlordane, and heptachlor exo- and endo-epoxide were analyzed using achiral and chiral high-resolution gas chromatography (HRGC) and detection by electron ionization (EI) and electron-capture, negative ionization mass spectrometry (ECNI MS). Two β-cyclodextrin (β-CD) derivatives were used as chiral selectors and dissolved in a polysiloxane stationary phase (PS086)

Enantioselective determination of chlordane components using chiral high-resolution gas chromatography-mass spectrometry with application to environmental samples

Technical chlordane was examined using both achiral and chiral high-resolution gas chromatography (HRGC) with detection by electron capture, negative ionization mass spectrometry (ECNI-MS). The enantiomer separation of several chiral octachlordanes including cis- and trans-chlordane was achieved and enantiomeric ratios of approximately 1:1 were determined using a modified β-cyclodextrin as the chiral selector. The method was then applied to tissue extracts of several aquatic vertebrate species collected from the Baltic Sea (herring, salmon, and seal) and from Antarctica (penguin).

Fast and precise determination of .alpha.-hexachlorocyclohexane enantiomers in environmental samples using chiral high-resolution gas chromatography

A high-resolution gas chromatographic method is described which allows the determination of the enantiomeric ratio of α-hexachlorohexane (HCH) in environmental samples within 18 min. A stationary phase with low bleeding was obtained by diluting permethylated heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin in a OH-terminated polysiloxane. It allowed temperature programming with detection in the low-picogram range using electron capture detection and high-resolution mass spectrometry. The separation method is compatible with standard sample cleanup procedures, which facilitate the reanalysis of stored sample extracts