摘要:

AbstractThis study comparts signal enhancement and efficiency in CZK employing three modes of detection: the sleeve cell (a simple method for creating a region of extended path length for absorption detection), the bubble cell (extended light path capillaries), and on‐column detection in 75 μm i.d. capillary. Flow profile in the sleeve cell was monitored under a microscope. An abrupt change in capillary diameter in the sleeve cell region (from 50 μm to 220 μm) did not produce extensive band broadening. The sleeve‐cell detection arrangement delivered a 3.5 fold increase in corrected peak area when compared with an oil‐column detection in 75 μm i.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200402

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

年代:1997

数据来源: WILEY

摘要:

AbstractSplitless injection conditions were optimized by the use of experimental designs (2‐level factorial and central composite designs). Modified parameters were: Type of liner, injection volume, solvent, temperature, splitless time. A prolonged splitless time, considered to be an important parameter, proved to be statistically insignificant. This leads to the conclusion that analytes can penetrate the dead volume between column entrance and split valve. To prevent any penetration of solvents, a small reversed split flow was introduced. It could be shown that this auxiliary flow allows an almost complete transfer of solvents. To further speed up the transfer process, a liner modification was propose

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200403

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

年代:1997

数据来源: WILEY

摘要:

AbstractCapillary gas chromatography (GC) combined with on‐column radio frequency plasma atomic emission detection was evaluated for the determination of polychlorinated and polybrominated biphenyls (PCBs and PBBs). Quantitation was possible utilizing a single chlorine or bromine calibration curve based on a randomly selected reference compound, because the signal per ng of halogen ranged within 17 % for 29 congeners. Combined with an internal standard to correct for potential plasma quenching from matrix components, this type of universal quantitation represented a sub‐stantial simplification of current calibration procedures. In combi‐nation with relatively low detection limits (1–5 pg/s of halogen), the present work suggested that GC, coupled with on‐column atomic emission detection is a promising technique for the determination of halogenated microp

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200404

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

年代:1997

数据来源: WILEY

摘要:

AbstractThree new chiral selectors, 6‐tert‐butyldimethylsilyl‐2,3‐diethyl‐a‐cyclodextrin, 6‐tert‐butyldimethylsilyl‐2,3‐diethyl‐ and dipropyl‐β‐cyclodextrin (TBDE‐α‐CD, TBDE‐β‐CD, TBDP‐β‐CD) were synthesized and tested as chiral stationary phases in capillary gas chromatography. TBDE‐β‐CD in particular showed a high enan‐tioselectivity for test chiral compounds due to good solubility in a polar polysiloxane (OV‐1701). Enantioselectivity obtained with TBDE‐β‐CD was compared with that of 6‐tert‐butyldimethylsilyl‐2,3‐di‐O‐methyl‐β‐cyclodextrin (TBDM‐β‐CD). Better enantiose‐lectivity was obtained with TBDE‐P‐CD than with TBDM‐β‐CD for the test chiral compounds studied. This is probably due to greater effect of the increased hydrophobicity of TBDE‐β‐CD which favors inclusion of the analytes than the effect of increased steric hindrance. With TBDP‐β‐CD the less polar lactones are well separated due most likely to increased hydrophobicity of the propyl groups while the more polar are not well resolved. For TBDP‐β‐CD it is likely that the unfavorable steric hindrance is predominant over the favorable hydrophobicity of the propyl groups, thus hindering the formation of inclusion complexes of the alcohols with TBDP‐β‐CD. TBDE‐α‐CD was also a valuable chiral selec

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200405

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

年代:1997

数据来源: WILEY

摘要:

AbstractVeltol® (2‐methyl 3‐hydroxy 4‐pyrone) and Veltol‐Plus® (2‐ethyl 3‐hydroxy 4‐pyrone) are patented flavor ingredients in food products. Only Veltol® can occur naturally, but both Veltol® and Veltol‐Plus® are often added to food products. In order to monitor the use of these compounds in food products, lower detection limits were needed. The Solid Phase Microextraction (SPME) technique for beverages and SPME coupled with Microwave Assisted Extraction (MAE) for solid food samples were studied. The influence of the pH, salt content, SPME adsorption time, GC inlet conditions, and the conditioning of the SPME fiber were investigated. Different food products were tested including coffee, beverages, chewing gums and potato chips. The coupled MAE and SPME shows good results for solid food samples. The reproducibility of the technique was less than 13%RSD and the detection limit was 10 ppb for Veltol® and 2 ppb for Veltol‐Plus® using the SIM mode in GC/MS. The technique also shows good selectivity for the target compounds investigated i

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200406

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe applicability of the retention index system to hcadspacc solid phase microextraxtion (HS–SPME) was investigated. In headspace SPME, the two equilibria gas phase/matrix and fiber coating/gas phase have to he considered. In this paper the equilibrium fiber coating/gas phase is discussed separately to characterize it more detailed and to investigate several methodical aspects. Therefore, the different distribution constantsKfiber/gasofn‐alkanes, which were used for reference compounds, were related to their Kováts retention indices. The validity of the derived linear relationship logKfiber/gasversus retention indexIis demonstrated for various examples. This relation is helpful for the assessment of distribution constants of substances not available and for the choice of a suitable fiber coating. Furthermore, quantification of analytes in the gas phase can be done without authentic substa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200407

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

年代:1997

数据来源: WILEY

摘要:

AbstractOff‐line normal‐phase LC has been used for the clean‐up of compounds in our laboratory for several years. On‐line coupling of this LC system, which typically yields 12 ml fractions, is not possible due to its large fraction volume. The maximum transfer volume in on‐line LC‐GC/ECD is approx. 300 μl. Therefore down‐scaling of the LC system was attempted in order to reach these low fraction volumes. Miniaturization resulted in a 240 μ1 LC fraction containing the analytes of interest, which is transferred to GC/ECD via an on‐column interface. Sensitivity requires that a minimum amount equivalent to 1–2 mg of sample should reach the GC detector; the selectivity is determined by the separation between the matrix and the last eluting target analyte.For the analysis of fatty samples, limitations were observed in the separation of dieldrin from triglycerides. Other organochlorine compounds, e.g. polychlorobiphenyls (PCBs), the DDT group, HCB and the HCHs can be analyzed with RSDs of 2–4 % (n = 10) at concentration levels of sub‐μ/kg in milk fat using a 3 μm Hypersil silica 5

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200408

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

年代:1997

数据来源: WILEY

摘要:

AbstractSalicylate is a hydrolysis product of salicylate‐containing drugs (such as aspirin) in patients' blood. Monitoring of this ion in blood is helpful for diagnosing of overdosage of these drugs. The present paper describes an ion chromatography (IC) method developed for determination of total salicylate in human serum, in which a hulk acoustic wave (BAW) sensor was used as detector; 0.5 mmoI/L sodium carbonate (Na2CO3, pH 8.5) served as mobile phase. Interference in the determination was negligible. The method is simple, rapid, accurate, and precise. Serum salicylate was analyzed using both the proposed IC‐BAW method and the classical Trinder spec‐trophotometric method, and the results showed that the two method agreed

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200409

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

年代:1997

数据来源: WILEY

摘要:

AbstractSupercritical fluid extraction of oxindole alkaloids fromUncaria Tormentosais described. The extraction was performed with supercritical carbon dioxide alone and with supercritical carbon dioxide modified with 10% metanol, and the extracts were analyzed by GC/MS and HPLC/MS.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200410

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

年代:1997

数据来源: WILEY

摘要:

AbstractA range of unusual fatty acids withcis‐5‐unsaturation had been reported in the seed oil ofCaltha palustris. Seed oils ofCimicifugaspp. have now been found to contain the same unusual fatty acids as are present inCaltha, plus several other minor fatty acids to give a more complex and more unsaturated seed oil fatty acid pattern.The gas chromatographic fatty acid patterns found seem to be consistent and chemotaxonomically significant, because essentially the same pattern was found in several species of the genusCimicifuga. These findings may shed a new light on the relation ofCimicifugatoCaltha, and to other genera in the plant family Ranunculaceae.The situation is illustrated by capillary GLC seed oil fatty acid methyl ester “fingerprints” obtained fromCimicifugaandCaltha, and is discussed in relation to other genera. The occurrence in nature of several of these unusual fatty acids, and their chemotax‐onomic significance is discussed. The close relation of GLC fatty acid patterns ofCalthaandCimicifugacould indicate monophyly and/or their belonging to the same tribe or subtribe. These observations are not in accordance with the phylogenetic systematic schemes of the genera in this plant family as published by variou

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200411

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

年代:1997

数据来源: WILEY