摘要:

AbstractAn automated large volume on‐column injection technique (LOCI) for capillary gas chromatography – mass spectrometry, GC‐MS, with solvent divert and heated retention gap technology has been used to simplify the method for determining sixteen neutral chlorinated extractable compounds (NCEC) in industrial plant process water samples at a level of 10 ng/L. According to the simplified procedure, 30 mL of water sample is extracted with 5 mL hexane, and 100 μL of the extract analyzed by combining large volume on‐column injection with mass‐selective detection operated in the selected ion monitoring mode. This combination has enabled simplification of the sample preparation and analysis procedures and provided a fast, labor‐saving technique for analyzing water samples. Simplifications include significant reduction of sample and eluent volumes during extraction, and elimination of theKuderna‐Danishevaporative concentration step. The latter simplification has not only resulted in significant time savings, both during the analysis and for subsequent glassware cleaning; analyte losses and the introduction of contaminants and artifacts which may occur during this step have also been eliminated.System behavior,e.g.linearity of detector response, method detection limit, and reproducibility, were evaluated for all sixteen analytes using spiked water samples in the lower ng/L range. The response of the mass detector is linear in the range 5–20000 ppt for all sixteen NCEC investigated. Injection of 100 μL of sample using LOCI makes it possible to achieve an instrument detection limit in the ppt range. The calculated method detection limits are similar to those of the instrument precision and are lower than the required method detection limit of 10 ppt.Extraction efficiency has been maximized by optimizing sample‐to‐solvent ratio and extraction time. The extraction efficiency seems to be independent of sample‐to‐solvent ratio in the range of 2. 5 to 6 and increasing the extraction time from 25 to 120 minutes resulted in no significant increase in efficiency. Extraction efficiency also seems to be independent of the concentration of analyte in the water samples. The simplified procedure presented here was automated by means of a laboratory robot and used to generate all the extraction data re

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171002

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

年代:1994

数据来源: WILEY

摘要:

AbstractA one meter stainless steel capillary column coated with a 20μm film of polydimethylsiloxane was used to replace the Teflon gas sampling loop of a HRGC – flameless SCD system. This column trap was equilibrated with the gaseous sample and then purged with carrier gas while being sequentially, resistively heated in ten 10 cm sections. The sequential heating of the 10cm sections was timed such that the velocity of the moving heated zone was approximately the same as the velocity of the carrier gas. The thick stationary phase film served to retard the front end of the injection band while the ballistic heating accelerated the back end. The net result was focusing of the injection, which gave rise to a narrower injection profile than that obtained with the original Teflon lo

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171003

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

年代:1994

数据来源: WILEY

摘要:

AbstractA new HPLC test has been developed for monitoring the racemiza‐tion which occurs during the coupling of Z‐Ala‐Trp‐OH with Val‐OMe by various methods. It is based on reversed phase HPLC separation of tripeptide diastereomers (LLL–LDL) and fluorescence rather than UV detection. The extent of racemization has been estimated for different carbodiimides, mixed anhydrides, and additive‐relea

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171004

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

年代:1994

数据来源: WILEY

摘要:

AbstractA series of non‐porous, microspherical zirconia‐based stationary phases with surface bound cationic functions have been introduced and evaluated in ion exchange chromatography of proteins and small acidic solutes. Different surface modification procedures were evaluated in the covalent attachment of weak, strong or hybrid anion exchange moieties on the surface of non‐porous zirconia micropar‐ticles.N,N‐Diethylaminoethanol (DEAE) was used as the weak anion exchange ligand while glycidyltrimethylammonium chloride, which was covalently attached to poly(vinyl alcohol) layer (PVAN) on the zirconia surface, constituted the strong anion exchange moiety. Partially quaternarized poly(ethyleneimine) hydroxyethylated (PEI) was used as the hybrid type of anion exchange coating. DEAE‐zir‐conia microparticles acted as purely cation exchange stationary phases toward basic proteins indicating the predominance of electron donor‐electron acceptor interaction (EDA) with surface exposed zirconium sites as well as cation exchange mechanism via electrostatic interaction with unreacted and unshielded hydroxyl groups. PVAN‐zirconia stationary phase exhibited anion exchange chromatographic properties toward acidic proteins, but EDA interaction has stayed as an important contributor to solute retention despite the presence of a relatively thick layer of poly(vinyl alcohol) on the surface of the zirconia particles. The modification of zirconia surface with partially quaternarized PEI proved to be the most effective approach to minimize Lewis acidic metallic properties of the support. In fact, PEI‐zirconia stationary phase operated as an anion exchanger toward acidic proteins and other s

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171005

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

年代:1994

数据来源: WILEY

摘要:

AbstractVery good separations of non‐ionic organic compounds have been achieved by capillary zone electrophoresis (CZE) using a tetrahep‐tylammonium salt as an additive in aqueous acetonitrile as solvent. A systematic study was undertaken to determine the effect of experimental parameters on electroosmotic mobility and electro‐phoretic mobility. It was found that pH, acetonitrile concentration, and the type and concentration of quaternary ammonium salt are important experimental variables. Under appropriate conditions, the separation window was enlarged and a broad range of electrically neutral organics, including very hydrophobic compounds (e. g. poly‐cyclic aromatic hydrocarbons) and fairly hydrophilic compounds were separated in a relatively short time. By adjusting the separation conditions, high resolution CZE of a specific group of neutral organic compounds could be achieved. A method for calculation of capacity factor was proposed and capacity factors for a variety of non‐lonic organic compounds were c

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171006

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

年代:1994

数据来源: WILEY

摘要:

AbstractA new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC‐11) has been prepared and coated on a fused silica capillary column. The main chroma‐tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC‐3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171007

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe effect of using ammonia as a carrier gas on the response of the flame ionization detector (FID) has been investigated. It was found that the FID response, calculated as the effective carbon number (ECN), increased for all the compounds studied when ammonia, rather than helium, was used. The change was 0–0. 9 carbon atom for hydrocarbons, one carbon atom for alcohols and diphenyl ether, and 0.4–1 carbon atom for phenols and ketones. The increase inECNwas larger for amines (0. 8–5 carbon atoms), but these numbers also reflected an improvement in chromatographic performance as a result of reduced adsorption on the column. The largest change in signal‐to‐noise ratio, a six‐fold increase, was obtained for octyl‐amine; ratios for hexyl methyl ketone, diisobutyl ketone, dihexyl‐amine, dibutylamine, andN‐methyloctylamine increased by a factor of 2–3 when ammonia was used as carrier gas. To determine the extent to which the effect on detector response was solely attributable to ammonia, a mixture of 5 % ammonia in nitrogen was used as detector make‐up gas with helium as carrier gas. Under these conditions the noise in the FID increased but for most of the compounds studied the signal‐to‐n

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171008

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

年代:1994

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171009

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

年代:1994

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171010

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

年代:1994

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240171011

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

年代:1994

数据来源: WILEY