摘要:

AbstractAn on‐line coupling of size‐exclusion Chromatography (SEC), normal‐phase liquid Chromatography (NPLC), and gas Chromatography (GC) for the characterization of complex hydrocarbon mixtures is described. The hyphenated system separates according to size, polarity, and boiling point. The use of size exclusion as the first separation step allows for the direct injection of complex (“dirty”) samples withont prior clean‐up. SEC‐NPLC coupling was realized using an on‐line solvent evaporator based on fully concurrent solvent evaporation (FCSE) using a modified loop‐type interface, vapor exit and co‐solvent trapping. Complete reconcentration of the analytes was realized by the introduction of a cryogenic cold trap. For the subsequent hydrocarbon group‐type separation an ammo‐silica column with n‐heptane as eluent was used. The NPLC‐GC coupling was based on an on‐column interface using partially concurrent solvent evaporation (PCSE) and an early vapor exit. Initial results obtained on the analysis of a residue from the atmospheric crude‐oil distillation (a so‐called long residue) are presented as an example of the enormous separation power of the SEC‐NPLC‐GC system. The application of the system for quantitat

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200302

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

年代:1997

数据来源: WILEY

摘要:

AbstractA modified sulfur chemiluniinescence detector (SCO) has been interfaced to a HPLC‐HRGC hyphenated system. This combination enables the full characterization and quantitation of the sulfur containing compounds in (heavy) middle distillate oil fractions (boiling range 150–450°C). The system is suited to identify and determine the various groups of orgaiio‐sulfur structures such as: thiols + sulfides + thiophencs, benzothiophenes, dibenzothiophenes and benzo‐naphthothiophenes. Within these groups a separation according to boiling point is accomplished. Therefore it allows the separation, identification and quantitation of a number of individual species, especially those which are refractory to hydrodesulfu‐rization (HDS), such as 3‐methyl‐benzothiophene, 4‐methyl‐dibenzothiophene and ‐J,6‐dimethyl‐dibenzothiophene. The analysis of these groups and specific compounds is the key in understanding the kinetics of the chemistry involved in HDS. The complete instrumental set‐up is fully automated by computer control. To suppress possible interferences and quenching of the sulfur response of the SCL from (large amounts of) hydrocarbons, it is aligned above the adapted flame ionization detector (FID) of the GC. This renders a sensitivity of the SCO for sulfur of 2 pg. s−1, which corresponds to a minimum detectable level for individual sulfur species in oil fractions for the complete system of 1 ppm (mg. kg−1) sulfur. Its linear dynamic range exceeds 105, which means that also untreated, high sulfur containing feedstocks can be analyzed directly. The selectivity of sulfur to carbon of the modified SCO exceeds 106. A number of HDS feedstocks and desulfurized products of different desulfurization levels have been analyzed with the system. From the analysis results the behavior of the refractory compounds in H

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200303

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

年代:1997

数据来源: WILEY

摘要:

AbstractLong‐term exposure to fat‐soluble xenobiotics is assessed by the concentration of DDE [1,1‐dichloro‐2,2‐bis(p‐chlorophenyl)ethyl‐ene], the persistent metabolite of DDT, in subcutaneous fat, aspirated from the buttocks of breast cancer patients and age‐matched controls, from five European centers collaborating in a case‐control study on breast cancer. In such studies using sample material of living subjects only small amounts of samples can be made available for analysis. In this particular study the only sample material available for the analysis of DDE were aliquots of the aspirates that were originally analyzed for fatty acids. Due to the small sample quantities available,e.g. aliquots of 200–800 p. 1, on‐line LC‐GC is most convenient because a major part of the sample can be used in the analytical procedure. In the LC‐GC procedure 50 μl of sample was injected on the LC column resulting in a 180 μl fraction containing the analytes of interest. The LC fraction was transferred to a capillary GC with electron capture detector by means of partially concurrent solvent evaporation. This way, sample handling is minimized thus reducing losses and preventing contamination. The feasibility of the on‐line LC‐GC system for the analysis of DDE is demonstrated with the analysis of 634 adipose tissue extracts in different series. The validity of this approach, using samples already analyzed for another parameter, with LC‐GC is clearly demonstrated by the fact that in over 97% of the samples DDE can be quantified. Thus rendering a meaningful data‐set for further epidemiological evaluation. The DDE levels found ranged

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200304

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

年代:1997

数据来源: WILEY

摘要:

AbstractThe equivalent chain length (ECL) values of the methyl esters of 83 defined fatty acids (FAs) have been determined by gas chromatog‐raphy (GC) on three fused silica DB‐WAX and three DB‐1 columns. ECL values of further 46 FAs were calculated by different methods. Conditions of chromatography, methods of ECL values calculation and differences between ECL values on individual columns and betweentrans‐ andcis‐isomers of corresponding FAs are also

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200305

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

年代:1997

数据来源: WILEY

摘要:

AbstractA simple method for the separation of highly hydrophobic neutral enantiomers by cyclodextrin‐modified micellar electrokinetic chro‐matography (MEKC) is presented and strongly supported by experiments. The separation depends on the ratio between the concentrations of cyclodextrin (CD) and sodium dodecylsulfate (SDS) micelles and there is an optimum value of the ratio for the separation of the enantiomers of norgestrel and 4‐androstene‐3,17‐dione. At the optimum value of the ratio, obtained by adjusting the absolute concentrations of CD and SDS. The electrophoretic mobility difference between two enantiomers can be maintained nearly

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200306

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

年代:1997

数据来源: WILEY

摘要:

AbstractTwo gas chromatographic methods, GC‐FID (flame ionization detection) and GC‐ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl‐methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC‐ELCD method and four decades with the GC‐FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC‐ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods

ISSN:0935-6304    

DOI:10.1002/jhrc.1240200307

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.1240200308

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.1240200309

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.1240200310

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.1240200311

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

年代:1997

数据来源: WILEY