ISSN:0935-6304    

DOI:10.1002/jhrc.1240131002

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

年代:1990

数据来源: WILEY

摘要:

AbstractA simple and versatile system is described for the on‐line coupling of SFE to capillary GC. The interfacing consists of a programmed temperature vaporizer (PTV) injector. With this injector it is possible to combine solute trapping, elimination of a high flow of extraction fluid, and quantitative transfer of solutes to the seperation column. The problems caused by impurities in the extraction fluid in on‐line SFE‐GC are discussed. Simple methods are described for the purification of commercially available carbon dioxide. The trapping efficiency of the PTV injector is studied. Applications of the SFE‐PTV‐GC system are given for the analysis of polymer anti‐degradants, polar compounds, and samples with environmenta

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131003

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

年代:1990

数据来源: WILEY

摘要:

AbstractA vacuum‐pump‐operated backflush system has been developed for applications involving high‐speed, repetitive GC analysis of gas streams containing ppm and ppb levels of organic vapor. The system uses an injector capable of cryofocusing and a relatively short length of 0.25‐mm i.d. fused silica column for the separation of relatively simple mixtures of volatile compounds. Analysis times typically are in the 5–10 s range, and backflush times are in the 2–5 s range. Gases from the flame ionization detector are used as the backflush carrier gas, and no modification of the detector is necessary. A procedure is described which allows the average gas velocity to be measured during backflush operation. The minimum backflush time is directly proportional to the analysis time and to the square of the column length, making this system most useful with short columns and short ana

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131004

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe composition of the mobile phase employed in capillary zone electrophoresis and the related technique, micellar electrokinetic capillary chromatography, is an important factor in determining separation performance. The influences of ionic salt, surfactant, and organic solvent mobile phase additives on separation efficiency, retention, and elution range are discussed and demonstrated.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131005

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

年代:1990

数据来源: WILEY

摘要:

AbstractSources leading to band broadening and peak distortion have been studied in a capillary column recycle system, based on a commercial microvalve. The ferrule system was a major contributor to band broadening. It was found that the quality of connections is very critical but the internal volume of the valve is not important. The pressure pulses resulting from each switching operation produced some band broadening with substances that had just been transferred through the valve but no adverse effects were noticed when they had travelled some distance into the column. Flow into valve cavities and through tees also produced a drop in efficiency. It is not clear whether this is solely due to problems in column connection or if changes in flow pattern also contribute.The activity of the valve toward polar substances was also assessed. No attempt was made to deactivate valve surfaces. The components of the Grob test mixture were almost unaffected but highly polar and acidic compounds such as nitrophenol showed severe losses. No evidence for catalysis was found.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131006

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe contribution ofextra‐column effects to the height equivalent to a theoretical plate (HETP) in capillary gas chromatography is calculated. Four extra terms are added to the Golay‐Giddings equation and evaluated in order to verify their significance. The paradox of negativeAterms is resolved by curve fitting of experimental values to the theoretical function of HETP, including theextra‐column effects. The importance of theAterm and the diffusion process for an injection in split mode were determined to be negligible compared to the other terms in the HETP equation. On the other hand,extra‐column contributions, proportional to the square of the gas velocity, are of significant importance. This contribution is inversely proportional to the column

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131007

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

年代:1990

数据来源: WILEY

摘要:

AbstractA novel modification of a hydrogen‐atmosphere flamo ionization detector (HAFID) is presented which attenuates response to hydrocarbon compounds, significantly enhancing selectivity towards organometallic compounds by more than an order of magnitude. Chromatograms of an organometallic compound test mixture and regular leaded gasoline are presented to depict the specificity of the respons

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131008

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

年代:1990

数据来源: WILEY

摘要:

AbstractAn experiment was designed to study the long‐term stability of analyses of pesticide residues in a complex food matrix using three different injection techniques. A spinach sample was spiked with five sulfur‐containing pesticides of varying volatility and thermolability: azinphos‐ethyl, dimethoate, methiocarb, ethiofencarb, and tri‐allate. Tri‐allate was selected as internal standard because of its thermal stability and its good chromatographic properties. Flame photometric detection resulted in chromatograms not subject to interference by peaks of compounds of the matrix. Starting with a clean and freshly, silanized injector an additional deactivation was found to occur on the first injection of a food sample resulting in an increased peak area for all pesticides in relation to tri‐allate. Highest long‐term stability was found with PTV injection. Best results for thermolabile carbamates were obtained using on‐column injection. However, they were prone to faste

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131009

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

年代:1990

数据来源: WILEY

摘要:

AbstractTransferring the site of specific substitution of dipentylated cyclodextrins with methyl or acyl residues from the secondary 3‐hydroxyl group to the primary 6‐hydroxyl group was expected to provide new information on the mechanism of chiral recognition. The 3‐position points towards and the 6‐position points away from the cyclodextrin cavity which via inclusion complex formation is supposed to play a major role in chiral separation. The “inverse” 6‐O‐acyl‐2,3‐di‐O‐pentyl‐cyclodextrins displayed almost no enantioselectivity but the corresponding 6‐O‐methyl derivatives are a versatile supplement to the chiral capillary GC phases nowadays available. Among the compounds that could be enantiomerically resolved are alcohols, amino acids, alkyl halides, bicyclic ethers, acetals, olefins, other hydrocarbo

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131010

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

年代:1990

数据来源: WILEY

摘要:

AbstractTwenty different tris(phenylcarbamate)s of cellulose were synthesized and evaluated as chiral stationary phases for HPLC. Optical resolving power of the tris(phenylcarbamate)s depends on the substituents introduced on the phenyl groups. Optical resolving abilities of amylose tris(phenylcarbamate)s were also evaluated. In most cases, either cellulose tris(3,5‐dimethylphenylcarbamate) or amylose tris(3,5‐dimethylphenylcarbamate) exhibited the highest optical resolving ability. Aralkylcarba‐mates such as benzyl‐ and 1‐phenylethylcarbamates of cellulose and amylose were also tested as chiral stationary phases. (S)‐1‐Phenylethylcarbamate of amylose showed a high optical re

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131011

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

年代:1990

数据来源: WILEY