ISSN:0935-6304    

DOI:10.1002/jhrc.1240151202

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

年代:1992

数据来源: WILEY

摘要:

AbstractFatty acids can be conveniently derivatized in less than one minute with (chloro)alkyl chloroformates such as methyl chloroformate, 2‐chloroethyl chloroformate and 2,2,2‐trichloroethyl chloroformate. 2,2,2‐Trichloroethyl chloroformate is the most reactive reagent, and yields a reaction product which can be sensitively detected by GC ECD (detection limit 50 ng/ml,i.e.25 pg/injection, for C8, C10, and C12acids).In non‐aqueous media 3‐picoline,N‐methylpiperidine, and dimethylaminopyridine show catalytic activity comparable with that of pyridine and can, therefore, replace it.N‐methylpiperidine is the best basic catalyst in aqueous media (i.e.media containing up t

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151203

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe development of tandem mass spectrometry (MS‐MS) and its combination with gas chromatography (GC‐MS‐MS) has greatly enhanced our ability to analyze exceedingly complex mixtures from a wide variety of sources, including fossil fuels. This paper describes a comparison of the conventional electron impact (El) mass spectral fragmentation patterns, obtained in the MS‐MS precursor – product mode, of three oleanane isomers and one ursene, all of which are used as indicators of higher plant input to the sedimentary environmentResults show that El and collision‐activated dissociation (CAD) spectra are most similar at collision energies between −15 and −20 eV.The presence of methyl substituents in these pentacyclic terpenes plays an important role in the process of ring fragmentation: the daughter spectra of the M – 15 fragments can be used to obtain structural information, such as the positions of

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151204

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

年代:1992

数据来源: WILEY

摘要:

AbstractThermal gradient programmed gas chromatography (TGPGC) separations involve the application of three‐dimensional thermal field programming. The operational aspects associated with TGPGC are such that rapid GC analyses can be achieved for complex and broad‐volatility‐range samples using open tubular columns with high thermal compliance, physical compactness, and geometric conformity. Elapsed times for TGPGC analyses of complex samples have ranged from 50 to 300 s. The application of rapidly changing thermal fields (or temperature surfaces) in TGPGC is accomplished through the use of a column sheath assembly. Recent research has centered upon different column sheath assembly designs and instrumental implementation of the TGPGC mode of operation. The instrumental implementation of the TGPGC mode for conducting GC and GC‐MS analyses places special demands upon the design and performance of numerous operational aspects of the system,e.g., the response‐time characteristics associated with analyte detection and the analytical output signal handling cap

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151205

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

年代:1992

数据来源: WILEY

摘要:

AbstractMore than 30 enantiomeric alcohols have been analyzed, without prior derivatization, by gas chromatography using a fused silica capillary column coated with octakis(3‐O‐trifluoro‐acetyl‐2,6‐di‐O‐n‐pentyl)‐γ‐cyclodextrin. Most were analyzed over a range of isothermal temperatures from 35 to 70°C. Enantiomeric separations were observed for most of the analytes, even at temperatures as low as 35°C.The stereoselectivity of the stationary phase was found to depend on the length of the longest carbon chain attached to the stereogenic centre in 2‐ and 3‐hydroxy alkanes, the relative positions of the methyl and hydroxyl substituents in methylsubstituted alcohols, and the effects of multiple bonds in the analyte molecule. Thermodynamic data calculated from the results suggest that the enantiomers of all the analytes are resolved by a similar process. Retention and thermodynamic data are presented and pos

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151206

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

年代:1992

数据来源: WILEY

摘要:

AbstractA novel integral restrictor–collector has been designed for use with a conventional supercritical fluid extraction (SFE) apparatus. The assembly reduces the path length between a micrometering valve and collector (a solid phase extraction (SPE) column), obviating the need for the complicated tubing and connectors usually associated with such devices. Also described is a heating‐block assembly which encases the micrometering valve and provides uniform heating of the valve during extraction.The valve–SPE column assembly was part of a system used to perform the first reported SFE multi‐residue drug recovery from fortified liver. Extractions used carbon dioxide pressurized to 690 bar as the supercritical fluid. Flow rates of expanded gas through the SPE columns were 3–4 L/min with concomitant quantitative trapping of the analytes on the sorbent bed. After SFE the three nitrobenzamide antimicrobial drug residues from the liver were eluted from the SPE columns by off‐line analysis. The results demonstrated that losses of trace level analytes in tissue may be significantly reduced by including an integral metering valve‐collector assembly as part of the

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151207

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe classical vaporizing injector has been modified for splitless injection of large volumes: during solvent evaporation in the packed vaporizing chamber, the carrier gas supply is interrupted and the septum purge outlet fully opened. This prevents vapors penetrating the gas regulation system and keeps the pressure increase in the injector to a minimum.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151208

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

年代:1992

数据来源: WILEY

摘要:

Abstract3‐Carboxy‐4‐methyl‐5‐propyl‐2‐furanpropionic acid (furanpropionic acid), a metabolite commonly found in human blood and urine, is one of the major acidic components which accumulates in the blood of patients with renal failure. Polyunsaturated fatty acids such as eicosapentaenoic acid (C20:5 ω−3) and long chain furan fatty acids, both present in commonly available fish oil capsules, are regarded as possible precursors of furanpropionic acid. Because of its strong binding to albumin and its various interactions with other endogenous and exogenous components, it is of great importance to determine the concentration of furanpropionic acid in blood and urine regularly.Solid phase extraction has been used to concentrate furanpropionic acid from both blood and urine samples. After esterification with ethereal diazomethane, gas chromatographic separation was performed on a HP‐1 column (dimethylpolysiloxane). Quantitation with an internal standard was performed by mass selective detection in SIM‐mode, qualifier ions being used for identification and accuracy.Fish oil supplementation of the diet of 24 patients for four weeks led to 3‐fold and 5 to 6‐fold increases in the levels of furanpropionic acid in serum

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151209

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

年代:1992

数据来源: WILEY

摘要:

AbstractSupercritical carbon dioxide and xenon are compared as mobile phases for SFC‐FTIR. Examples are presented illustrating the use of xenon in SFC and it is compared with carbon dioxide for a range of compounds of different polarities. Investigations of the effects of mobile phase temperature and density on infrared spectra measured in supercritical solution are also presented.It has been found that carbon dioxide gives smaller shifts with temperature and density changes than had been reported previously and that carbon dioxide and xenon give rise to remarkably similar effects in almost all circumstances. A comparison of SFC‐FTIR spectra with vapor‐ and condensedphase data is presented and it is shown that such data will require modification to model the effects of the supercritical solvent. The study shows that such modification should be relatively straightfo

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151210

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

年代:1992

数据来源: WILEY

摘要:

AbstractLiquid – liquid extraction withN‐methyl‐2‐pyrrolidone, combined with solid‐phase extraction on silica gel usingn‐pentane and dichloromethane as solvents, has been used for the isolation and concentration of the aromatic fraction from lubricating oil.The identification of individual compounds in this aromatic fraction was performed by capillary gas chromatography–mass spectrometry (CGC‐MS) and by determination of retention indices. Quantitative results were obtained by flame ionization detection (CGC‐FID). Eighty four compounds, predominantly naphthalenes, phenanthrenes, biphenyls, fluorenes, dibenzo‐thiophenes, and their alkylated derivatives, have been identified in a commercial lubricating oil. The total amount of the aromatic fraction did not excee

ISSN:0935-6304    

DOI:10.1002/jhrc.1240151211

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

年代:1992

数据来源: WILEY