摘要:

AbstractThe potential of enantioselective capillary gas chromatography with modified cyclodextrins as chiral stationary phases for authenticity control is demonstrated for a selection of economically important essential oils. Adulteration can be easily detected in cases where enantiomerically pure constituents are present in natural oils. In cases of (naturally) varying enantiomeric compositions of chiral constituents, enantioselective gas chromatography may prove insufficient.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200202

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

年代:1997

数据来源: WILEY

摘要:

AbstractArtemisinin (an antimalarial compound) and its bioprecursor artemisinic acid, present in the plant Atemisia annua L., were analyzed by supercritical fluid chromatography (SFS) using capillary and packed columns, coupled respectively with a flame ionization detector (FID) and an evaporative light scattering detector (ELSD). Both methods were optimized and validated with columns of different polarity in order to separate artemisinin and artemisinic acid. Analytical results were comparable, but the paced SFC‐ELSD method was faster. Indeed, artemisinin and artemisinic acid were separated with an aminopropyl silica column in less than 8 minutes instead of about 25 minutes by capillary SFS. Contrary to conventional gas and liquid chromatography coupled to an UV‐visible detector, SFS methods determined both compounds directly, without degradation and/or derivatization in the concentration range expected in the plant material. Results obtained on plant extracts by capillary SFS‐FID and packed SFS‐ELSD were confirmed b

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200203

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe aim of this work was to characterize the fulvic acids (FA) extracted from peat by use of capillary electrophoresis (CE). Two FA extracts have been obtained using two different extractants (0.1 M NaOH and 0.1 M NaOH plus 0.1 M Na4P2O7, Na+PP). The CE runs wre performed using a coated silica capillary, and several buffer solutions at different PH values. The results obtained show that the Fa extracts may be well characterized by CE even if the isolelectric point of the fulvic compounds is very low. The best fractionation has been obtained using a buffer borate at PH 8.9 as funning buffer. The charcterization of the two extracts also showed some important differences between the NaOH extract and the Na+PP extract.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200204

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

年代:1997

数据来源: WILEY

摘要:

AbstractSeveral acidic xylooligosaccharides containing unsaturated “hexenuronic acid” units, i.e. 4‐deoxy‐L‐threo‐hex‐4‐enopyranosy‐lurinic acid (4‐ΔU) units, were separated as their alditol derivatives by capillary zone electrophoriesis in 438 mM borate buffer (pH 10.3) and were detected selectively at the μM level on‐column UV detection at 232 nm. These acidic oligosaccharides were obtained from birch and pine kraft pulps on enzymatic hydrolysis with endoxylanases and subsequent treatment with other Trichoderma reesei enzymes. Under the conditions empolyed, acidic 4‐ΔU‐containing xylooligosaccharides with a molecular size renging from trisaccharides up to nonasaccharides could be separated. Oligosaccharides with higher molecular mass were detected first. Two 4‐ΔU‐xylotetraose isomers, with the 4‐ΔU‐group linked to different xylose units in the iligosaccharide backbone, could be resolved from each other with a resolution of about 1. By using a disaccharide (4‐ΔU α‐(1 → 4) linked to N‐acetyl glucosamine) as a model compound the minimum

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200205

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe initial width of the injected solute bands is a major determinant of the final measured peak width. While the individual processes contributing to this intial width have been observed and described qualitatively by many authors, little attention has been focused on their quantitative relationship. Using solid phase microextraction (SPME) and splitless injections of a hydrocarbon test mixutre the contributions to overall peak variance in SPME and splitless injections can be separated and quantitated. In SPME, it is seen that thermal focusing or rapid desorption must serve to provide focused bands. In splitless, thermal fucusing and solvent effects provide focusing. Variance contributions for each of these are calculated and shown.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200206

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

年代:1997

数据来源: WILEY

摘要:

AbstractCapillary gas chromatography in combination with atomic emission and electron impact‐chemical ionizaion mass spectrometry detectors have been used to detect amitraz degradation products in honey storage, characterize their structure, and evaluate their occurrence over a 100 day peroid. To this end, honey samples were extracted with an 8:2v/vn‐hexane/acetone mixture. Amitraz was found to be rapidly decomposed into five related compounds, of whichN‐(2,4‐dimethylphenyl)formamide was the most abundant and per

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200207

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

年代:1997

数据来源: WILEY

摘要:

AbstractFour chiral stationary phases containing modified cyclodextrines diluted in or chemically bonded to a non‐chiral phase were used to resolve chiral organochlorine compounds such as α‐hexachlorocyclohexane (α‐HCH), perdeuterated α‐HCH (α‐PDHCH), β‐and γ‐pentachlorocyclohexene (PCCH), oxychlordane, cis‐andtrans‐chlor‐ dane, cis‐ andtrans‐heptachlorepoxide, PCB 95, PCB 132, PCB 149, and Chiral tozaphenes.The elution order was determined by analyzing standards with known enantiomeric excesses.Furthermore, an internal standard was used to even out slight variations in the ratio of peak hights of enantiomers which were determined from injection to injection.None of the chiral stationary phases resolved all chiral organochlorine compounds. However, the β‐TBDM(35% heptakis (6‐O‐t‐butyldimethylsilyl‐2,3‐di‐O‐methyl)‐β‐cyclodextrin in OV 1701) column allowed the separation of all compounds under investigation except for PCB 95 and chiral toxaphenes.Emphasis was placed on the separation of as many as possible enantiomers on a chiral phase by application of one temperature program and with respect to unambiguous quantitation of biological samples such as

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200208

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

年代:1997

数据来源: WILEY

摘要:

AbstractA method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off‐line preconcentration step by means of a closed‐loop trapping system followed by gas chromatography‐ion trap detection. With the closed‐loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology.By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200209

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

年代:1997

数据来源: WILEY

摘要:

AbstractSome data on a newly developed filter/sorbent indoor air SVOC sampling device for thermal desorption analyiss are described. Thermal desorption of SVOCs spiked on Tenax had reponse factors identical to on‐column injection except for highly polar compounds like fatty acids. SVOCs spiked on quartz fiber filters had response factors that on an average were 80% of the on‐column response factors (66% for oxygen containing compounds and 87% for non‐oxygen compounds) Low nanogram on‐tube amounts of SVOCs were found generally to have lower recoveries than larger amounts from both Tenax and quart fiber filters. This appeared to be explained in part by a relatively larger “memory” effect and lower desorption efficiency. In addition, it was indicated that the “memory” effect was an important source of background contaminations that might impair analysis of low nanogram on‐tube amounts of some SVOCs. Polar SVOCs. Polar SVOCs in the gas phase appear to adsorbto the quartz fiber filters. This functions as a precleaning of the sample and thus minimizes the problem with coeluting peaks. The relative standard from nine duplicate samples appeared to be sufficiently low to distinguis

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200210

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe composition and concentration of polycyclic aromatic compounds (PAC) in fuels. Theier combustion products and in the atmosphere remains a topic of considerable interest. Despite the wealth of literature on the identification of PAC, speciation at low concentrations remains difficult due to instrument limitation and the complexity of fuel and environmental samples. Consequently on line sample preparation procedures (SPE, SFE, LC,etc.) are becomeing an increasingly important step in the analysis procedure particularly where sample clean‐up and fractionation are essential for improving analytical resolution. In this study a normal phase high pressure analytical resolution. In this study a normal phase high pressure liquid chromatography‐gas chromatography (LC‐GC) system has been developed to provide quantitative analysis of samples, as diverse as coal liquids, petroleum fuels, diesel exhaust particulates, and urban air particulates. Separation and identification of parent and alkylated PAH, hetercycline nitro‐and oxy‐PAC can be achieved by direct coupling to an atomic emission detector and a bech top mass spectrometer. For both systems the primary LC separation combined with the large sample volume transferred to GC vastly improves detection limits. Furthermore the complimentary nature of the two detectors used enables the positive indentification of many

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200211

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

年代:1997

数据来源: WILEY