摘要:

AbstractA method combining the techniques of liquid – solid disk extraction (LSDE) and supercritical fluid elution (SFE) has been developed for the phenols regulated by the Clean Water Act. LSDE uses a disk or membrane made of polytetrafluoroethylene (PTFE) fibrils impregnated with small particles, e.g. styrene divinylbenzene (SDB) resin, to extract phenols from water. After disk extraction the retained analytes are eluted from the disk using SFE. SFE is used as an alternative to liquid solvent elution with an organic solvent. Analytes are separated, identified, and quantified using gas chromatography – ion trap detector mass spectrometry (GC‐ITDMS). The method is capable of sub parts per billion detection limits, and precision of 5–28%RSD.Evaluation of various disks or membranes, such as C18‐silica disks, SDB disks, and ion exchange membranes, has also been performed for the extraction of phenols from water. The results obtained from thein‐situaqueous acetylation of phenols and extraction of their acetates are quantitative. The utilization of LSDE and SFE techniques has proven to be a more effective approach than liquid – liquid extraction in minimizing air pollution and

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170702

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

年代:1994

数据来源: WILEY

摘要:

AbstractFatty acids from blood serum lipids and fish oil preparations are derivatized with 2‐amino‐2‐methyl‐1‐propanol to form 2‐substituted 4,4‐dimethyloxazolines. The derivatives are separated on a 25 m × 0.25 mm FFAP column and identified by mass spectrometry using electron impact ionization. The positions of the double bonds of mono‐ and polyunsaturated fatty acids can be easily and reliably recognized from a characteristic fragmentation feature of the oxazolines. Several unsaturated C16 to C22 fatty acid isomers are identified whose exact structure has not been derived from the commonly us

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170703

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn trace analysis by capillary GC it is often desirable to use larger than normal injection volumes to obtain sufficient sensitivity. This, however, results in a wider solvent peak and tailing, and may reduce column efficiency. This paper describes the use of a short length of a capillary precolumn coated with a stationary phase of polarity similar to that of the sample solvent and a film thickness greater than that of the analytical column; provided the right combination of polarities of injection solvent and liquid phases are used, the precolumn focuses the solvent band, thereby enabling the maximum injection volume to be increased without measurably reducing efficiency. Typical precolumn dimensions are 1 m length, 0.32 mm i.d., and 0.5 μm stationary phase film thickness. Using a precolumn increases the maximum injection volume up to 8 or 10 μl, or three times that appropriate for a conventional analytical column, with little or no loss in efficienc

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170704

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

年代:1994

数据来源: WILEY

摘要:

AbstractAs part of a continuing evaluation of new analytical and sample preparation techniques conducted by the US Environmental Protection Agency (EPA), the use of capillary gas chromatography with atomic emission detection (GC‐AED) for the simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples was investigated. Pentylmagnesium bromide was used to pentylate ionic organotin, organolead, and organomercury compounds; the pentyl derivatives were then separated by GC and determined by AED. Several important GC‐AED parameters, including the type of injector inlet, carrier gas flow rate, and helium make‐up gas flow rate, were optimized for the simultaneous determination of these organometallic compounds. Their minimum detectable concentrations were approximately 1.0 to 2.5 ng/mL using a 0.5‐μL on‐column injection. The calibration curves exhibited good linearity between 2.5 and 2500 ng/mL for organotin and organolead compounds, and between 2.5 and 10000 ng/mL for organomercury

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170705

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe counter ion in CZE separation systems affects resolution, effective field strength and electroosmosis. Alkali metals (lithium, sodium, potassium, and cesium), the ammonium ion, and several complexes of metals with ammonia ([Ag(NH3)2]+, [Cu(NH3)4]2+, [Zn(NH3)4]2+, [Cd(NH3)4]2+, [Ni(NH3)6]2+, and [Co(NH3)6]2+) have been studied for their effect on the separation of diuretics. With the alkali metals the electroosmotic flow velocity decreased and the effective field strength and resolution increased as the hydrated radius of the alkali metal decreased.All the metal‐ammonia complexes except that with silver greatly reduced the electroosmotic flow velocity (Veo) and had only a slight effect on the effective field strength (Eeff). Because these complexes had a negligible effect on the ionic strength of the buffer, they enabled high separating power to be maintained during the separation, and hence the use of more energy in the separation system. This yielded better resolution of the compounds, but the analysis time was then compromised.A simultaneous reduction in capillary length andVeowhile maintaining the high voltage enabled increased resolution without an increase in analysis time. The ability to controlVeoby adding small concentrations (<100 μM) of metal complexes to the buffer solution makes it possible to adjust the analysis time and capillary length independently while employing high separation pow

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170706

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

年代:1994

数据来源: WILEY

摘要:

AbstractIdentification ofcis/transisomers of unsaturated fatty acids cannot usually be achieved by GC‐MS (gas chromatography‐mass spectrometry) without reference substances. In this study a GC‐FTIR‐MS system (gas chromatography‐Fourier transform‐mass spectrometry) was used to identify fatty acid methyl esters (FAMEs) and differentiate between thecis/transisomers. Besides methyl esters, 2‐alkenyl‐4,4‐dimethyloxazoline derivatives (DMOX), which have been used to locate double bond positions of unsaturated fatty acids, were examined with respect to their suitability forcis/transdifferentiation.A combined GC‐FTIR‐MS system with a wide band (4000–550 cm−1) mercury cadmium telluride (MCT) detector was used in series and parallel to identify 31 reference unsaturated fatty acids, including 7 pairs ofcis/transisomers. Serum samples of healthy persons and commercially available fish oil were analyzed as examples of complex mixtures. Using splitless injection the detection limit for the less sensitive IR detector was 25 ng/μl in case of the weakcisandtransbands.In the FTIR spectracis/transisomers were identified by analysis of bands arising from CH out‐of‐plane (oop) bending: for both the FAME and DMOX derivativescis‐1,2‐disubstituted double bonds give a strong band near 720 cm−1and the correspondingtransisomers near 967 cm−1.cisIsomers could be identified further by a band at 3012 cm−1. With the combined data of the GC‐FTIR‐MS system it is now possible to identify polyunsaturated fatty acids with r

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170707

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

年代:1994

数据来源: WILEY

摘要:

AbstractSeries of C‐ring monoaromatic steroid hydrocarbons (C21, C22, C27 C29) and triaromatic steroid hydrocarbons (C20, C21, C26 C28) have been recognized in the aromatic hydrocarbon fraction of Alamein crude oil from the western desert, Egypt. Detection of these compounds were based on mass fragmentography of the key ionsm/z253 andm/z231 and comparison of the mass spectra and relative retention times with literature data. The predominance of the C29monoaromatic steroids and C28triaromatic steroids provide further evidence for a land plant origin of Alamein oil. The results substantiate previous evidence of the occurrence of an aromatization process with increasing maturation and indicate a moderate maturity level for Alamei

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170708

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

年代:1994

数据来源: WILEY

摘要:

AbstractA capillary gas chromatographic method has been developed for the determination of glycerol, erythritol, arabitol, sorbitol, and inositol in vinegar. After addition of phenyl‐β‐glucopyranoside as internal standard, the sample was then dried and silylated. The analysis was performed both on the crude silylated sample and after liquid – liquid extraction. The repeatability of the two methods was evaluated on twenty three different types of vinegar and the extraction did not seriously affect the analysis. Extraction of the TMS‐ethers enables elimination of a large number of interfering substances such as acids and polyphenols and so acts as a purification of th

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170709

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

年代:1994

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170711

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

年代:1994

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170712

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

年代:1994

数据来源: WILEY