ISSN:0935-6304    

DOI:10.1002/jhrc.1240140702

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

年代:1991

数据来源: WILEY

摘要:

AbstractTotal lipids have been extracted from human serum with chloroform–methanol 2:1 (v/v) and separated into individual classes by TLC. After transesterification the fatty acid methyl esters were analyzed by capillary gas chromatography on an FFAP column. The quantitation of ω‐3 fatty acids has been performed using internal and external standards. Internal lipid standards for each lipid class were carried throughout the entire analytical procedure. Under normal diet eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are incorporated into the lipid classes to different extents: cholesterol esters; EPA, 6.5 ± 1.9 γ/ml serum; DHA, 4.3 ± 1.9 μg/ml: phospholipids; EPA, 5.9 ± 2.7 μg/ml; DHA, 31.8 ± 8.1 μg/ml. Fish oil supplementation leads to a 4 to 6‐fold rise in EPA and to an approximately 2‐

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140703

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of the pressure drop across the column on retention and efficiency in SFC have been studied. Numerical methods are described which enable the prediction of hold‐up time and pressure drop in both packed and open tubular columns. Predictions of both hold‐up time and pressure drop are in good agreement with experimental data.The density gradient along the column can be calculated using the numerical methods and a procedure is described which enables the calculation of the overall capacity factors of the solutes from the density profile in the column. Significant variations of the capacity factor are observed along the column.The effect of the density gradient along the column on local diffusivity and dispersion is studied. The column efficiency in systems with significant pressure drops is affected by changes in: the linear velocity of the mobile phase; the diffusion coefficients; and the capacity factors of the solutes along the column. The overall efficiency of the chromatographic system can be calculated if, as is the case for open tubular columns, adequate plate height equations are availa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140704

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

年代:1991

数据来源: WILEY

摘要:

AbstractAir and surface samples taken following indoor applications of natural pyrethrins and pyrethroids have been analyzed by HRGC‐ECD and HRGC‐MS using negative chemical ionization (NCI). It has been found that pyrethroids persist on surfaces as long as sixty hours after application.Primary pyrethroid degradation products have been characterized by mass spectrometry; their identities and route of formation by ozonolysis have been verified by degradation studies and

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140705

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

年代:1991

数据来源: WILEY

摘要:

AbstractSEC is used for clean‐up of food extracts obtained for analysis of pesticide residues primarily to remove high molecular weight material, among which fat may be present at the largest concentrations. The triglyceride peak, which is usually very large, is eluted before the components of interest. The problem described in this paper deals with the tail of the triglyceride peak: this may intrude into the fraction containing the pesticides and contaminate the G

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140706

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

年代:1991

数据来源: WILEY

摘要:

AbstractA new approach to the introduction of large aqueous samples into a gas chromatograph, solid phase extraction ‐ thermal desorption, is presented. Carrier gas pushes the sample through a packed liner mounted in a programmed temperature vaporizer; analytes retained by the packing material are thermally desorbed after drying of the adsorbent. The sorption properties and thermal stability of some packing materials have been studied off‐line. Tenax GC®, and octyl‐modified silica silylated with diphenyltetramethyldisilazane to improve its thermal stability, appeared to be suitable materials.The drying period and the desorption temperature are critical for satisfactory performance of the method. When Tenax GC® is used as packing material, thermal desorption at 250°C for 15 min gives quantitative recovery for methyl esters up to hexacosanoic acid methyl ester. With the silylated octyl‐modified silica, the application range is limited to the methyl esters of decanoic to octadeca

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140707

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

年代:1991

数据来源: WILEY

摘要:

AbstractMicrocolumn liquid chromatography (micro‐LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro‐UV cell coupled on‐line to a thermionic detector (TID). Micro‐LC showed aca.5‐fold improved separation impedance, aca.1.8‐fold increased column permeability, and greater inertness compared with conventional LC.By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro‐LC‐TID system is linear in the range of 0.05–

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140708

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on‐line to capillary GC‐ECD by means of a loop‐type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean‐up of the extracts analyzed.By means of solid‐phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron‐capturing compounds present in the water at ppt levels. ASPEC‐GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water.The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140709

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

年代:1991

数据来源: WILEY

摘要:

AbstractNucleic acid compositional analysis is discussed, followed by a brief review of the current state of the technology applied in which the benefits and limitations of current methodology are enumerated. An alternative method is presented, namely the use of a micropacked capillary ion exchange column to separate nucleoside monophosphatesviaan anion exchange mechanism. The separated nucleotides are then quantitated by means of post‐column photodiode‐array detection. The use of a photodiode array also enables the verification of peak identity and purity by acquisition of UV spectra at any point in the separation. The technique has applications in the compositional analysis of both deoxyribonucleic acid (DNA) and ribonucleic acid (R

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140710

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

年代:1991

数据来源: WILEY

摘要:

AbstractA new technique for coupling reversed‐phase liquid chromatography (RPLC) with gas chromatography is described. A fraction eluting from an RPLC column is trapped on a short column packed with polymeric adsorbent. After the mobile phase has been displaced with water, the analytes are desorbed with ethyl acetate. Following a delay time to enable the water to be flushed to waste, the ethyl acetate containing the analytes is introduced into the gas chromatograph under conditions suitable for partially concurrent solvent evaporation,i.e.below the solvent boiling point and at a rate just exceeding the evaporation rate. Post‐column addition of water to the RPLC eluent helps to prevent breakthrough of compounds which are only modestly retained on the trapping column. The relationship between the capacity factors of the analytes on the trapping column and the required dilution factor is discussed. Polycyclic aromatic hydrocarbons are used as test compounds to study the sys

ISSN:0935-6304    

DOI:10.1002/jhrc.1240140711

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

年代:1991

数据来源: WILEY