摘要:

AbstractThe enantiomeric distrubution of solerone (5‐oxo‐4‐hexanolide) 1, ethyl 4‐hydroxy‐ 5‐oxohexanoate 2, ethyl 5‐hydroxy‐4‐oxohexanoate 3, 4‐oxo‐5‐hexanolide 4, and solerol (5‐hydroxy‐4‐hexanolide) 5 in sherry wines was determined by several HRGC techniques. While gas chromatography‐mass spectrometry on chiral cyclodextrin phases (chiral GC‐MS) prevented any racemization of α‐ketols 2 and 3 caused by keto‐enol tautomerization during analysis, multidimensional gas chromatography MDGC (coupled either by “live‐T” switching or by “moving column stream switching” MCSS) led to rearranged constitutional‐and stereoisomers. The stereochemical results are discussed r

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractMaple SyrupUrine disease (USUD) is an autosomal recessive inherited metabolic disorder of branched‐chain amino acid (L‐valin, L‐leucine, and L‐isoleucine metabolism named after the characteristic smell of affected patients urine. MSUD is caused by a deficiency of the branched‐chain α‐keto acid dehydrogenase compex resulting in an accumulation of branched‐chain aamino acids and the corresponding α‐keto‐and α‐hydroxy acids in blood, urine and cerebrospinal fluid causing neurological damage and mental retardation. The enantioselective analysis of chiral MSUD metabolites and analysis of achiral compounds as correspondingN,O‐methoxycarbonyl methyl esters by derivatization with methyl chloroformate (MCF) has been achieved simultaneusly by enantioselective multidimensional gas chromatography‐mass spectrometry using heptakis (2,3‐di‐O‐methyl‐6‐O‐tert‐butyl‐dimethyl‐silyl)‐β‐cyclodextrin as chiral stationary phase. Derivatization with MCF allows the analysis of the structurally different metabolitetes such as branched‐chain‐carboxylic‐, α‐oxo‐, α‐hydroxy‐ and α‐amino acids in a single chromaatographic run. Mass selective detection immensely improves the unequivocaaal identification of metabolites even when they occur as trace compound. The described method allows a reliable screening of MSUD metabolites in patients' urine without time consuming sample preparation and is also suitable for label enrichment analysis without any methodical changes. During thi

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractAn automated system for derivaatization was coupled on‐line with solid‐phase extraction‐gas‐chromatography (SPE‐GC). The system was optimized for the determination of phenol and chlorinated phenols in aqueous samples. The test analytes were acetylated with acetic anhydride; proper buffering of the sample was a critical factor. Next, the phenol acetates were enriched on a SPE cartridge and transferred to a GC; two appraoaches were studied. In the first approach, the derivatives were enriched on disposable C18 cartridges (ASPEC type) and desorbed with methylacetate. Aan aliquot of the final eluate was injected on‐line the GC by means of a loop‐type interface. In the second approach, trace enrichment was performed on 10 × 2 mm i.d. LC‐type precolumn packed with polystyrenedivinylbenzene copolymer (PLRP‐S) this precolumn was dried with a mitrogen purge and the phenol acetates were desorbed with ethyl acetate which was injectedon‐line into the retention gap of the GC under partially concurrent solvent evaporation (PCSE) conditions. The Derivatization‐SPE‐GC system which was based on the loop‐type interface has the advantage of simplicity and easy operation, the main drawback is the impossibility to determine phenol acetates which elute prior to trichlorophenol acetates. With the derivatization‐SPE‐GC approach using PCSE‐based desorption, even the most volatile analyte of the test series, phenol acetate, can be determined successfully. The entire procedure, including the derivatization step, was fully automated and integrated in one set‐up. The precision data for the integrated on‐line derivatization‐SP‐FID system were fully satisfactory, with RSD values of 1–12 % at the 1 μg/1 level. When a sample volume of 2.2 ml was analyzed, The detection limits for the chlorinated phe

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractToxicity evaluation of Dicofol toAstyanax bimaculatus schubarti, a characteristic fish species living in tropical rivers and lakes was carried out through LC50– 96 Hours. These experiments were performed under laboratory controlled conditions with atmospheric air flow and dilution water at 25°C in the static mode, supercritical fluid extraction (SFE) with pure CO2and CO2modified with hexane and methanol were used at 50, 70, 80, and 100°C and 300 atm. Several collection modes were studied to extract Dicofol from fish samples. The extraction efficiencies were directly comparedd with those obtained after 8 h of Soxhlet extraction using the same clean‐up with Florisil and analysis by HRGC/ECD and HRGC/MS as a confirmatory analytical technique. The SFE recoveries at temperatures lower than 80°C were typically lower than soxhlet recoveries; however a temperature increase enhanced the efficiency of SFE. The results showed that under certain conditions, supercritical fluid gave higher extractio power (extracted 11 % more pesticide), shorter extraction time, and lower solvent consumption than Soxhlet, thus affording an excellent alternative to the conventional method for extracting Dicofol from fish

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this study, it is shown that calibration solution prepared in control matrix extrix extract can be used to compensate for matrix‐induced chromatographic response enhancement observed for certain pesticedes. This phenomenon is characterized by enhanced chromatographic response for certain pesticides in the presence of matrix du to reduced analyte loss during injection. Unacceptably high recoveries are seen for affected pesticides when maatrix‐free solutions are used for reference and calibration. The effects of matrix concentration on overall enhancement and linear response were determined. When used as reference standards for the determination of recovery, matrix‐standard solutions were found to provide acceptable recoveries for pesticides subject to matrix‐induced chromatographic response enhancement along with other pesticides. General guidelines are presented for using matrix‐standard calibration solutions in pesticide residue

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractThe gas Chromatographic properties of five laterally substituted liquid crystals are the subject of a comparative study. These liquid crystals belong to the homologous series: 2‐alkoxy‐3‐methyl‐4‐(4‐ethoxybenzoyl‐oxy)‐4′‐(4‐trans‐n‐pentyclcyclohexanecarboxyloxy) azobenzene, referred to as ALn, wheren, the carbon number in the lateral alkoxy chain, is equal to 4, 6, 8, 10, or 12 carbon atoms. Their thermal properties were established by differential scanning calorimetry (DSC). It appears that the introduction of a lateral alkoxy chain affects the nematic temperature range which decreases when the carbon number increases. The chromatographic separation abilities of AL4, AL6, AL8, AL10, and AL12 were studied using capillary glass columns. The five liquid cystals are efficient before and after solid‐nematic or nematic‐liquid transitions; however, the plate numbers are higher in the nematic state. Interesting analytical properties were noted in various fields: iisomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds, andcisandtransisomers. However, the chain length does not exert any great influenc

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

摘要:

AbstractA new method for the preconcentration of trace components from gaseous samples is described. The system is based on enrichment of the solutes on a packed bed of 100% polydimethylsiloxane (PDMS) particles followed by thermal desorption and GC analysis. It was demonstrated that breakthrough volumes for packed PDMS traps can be calculated from theoretical equations. The PDMS material exhibits excellent thermal stability even after 200 consecutive runs. Additional advantages of packed sorbent beds over conventional adsorbent materials include high inertness, the absence of displacement effects and a reduced affinity for water. The practicality of the system was demonstrated by the analysis of air and natural gas using the system described here, components in the range of octane to benso[a] pyrene could be quantitatively trapped and thermally desorbed at mild temperatures. With the present set‐up the detection limit is in the order of 0.1 ng/m3(MSD detector

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200711

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1997

数据来源: WILEY