ISSN:0935-6304    

DOI:10.1002/jhrc.1240141202

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe sensitive detection of sulfur‐containing analytes is of interest in many industrial applications; selective detection is also desirable since these compounds are usually present at trace levels in difficult matrixes. The purpose of this article is to review the use of the Sievers® ozone‐based sulfur chemiluminescence detector, and its coupling with gas chromatography, supercritical fluid chromatography, and high performance liquid chromatography. Detection limits, linearity, response factors, and selectivity are discussed for each of these techniques. Critical operational parameters for the SCD are also described. The use of other sulfur selective detectors for SFC and HPLC is also briefly summar

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141203

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

年代:1991

数据来源: WILEY

摘要:

AbstractSuccessful separation of the six major hop bitter compounds by micellar electrokinetic chromatography depends critically on precise pH control. Any factor which can affect the actual in‐column pH must, therefore, also be carefully controlled: it has been found that temperature‐induced changes of the buffer pH can cause loss of resolution and even reversals in elution order. The pH level at which the effects occur suggests that the pKa values of the analytes are modified by the micellar med

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141204

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

年代:1991

数据来源: WILEY

摘要:

AbstractA rapid, precise method has been developed for the determination of the fatty acid profile of small samples of milk fat. Lipids are extracted from milk withn‐hexane, triglycerides are trans‐esterified with sodium methoxide, and free fatty acids are esterified with methanolic hydrochloric acid. The methyl esters are separated on a narrow‐bore, 5% phenyl polydimethylsiloxane capillary column. The fatty acid profile is precise: for the various acids the coefficients of variation of peak area are between 6.7% and 9.7%, with a mean of 8.1%, and the coefficients of variation of peak percentage area are between 0.3% and 5.5% with a mean of 1.8%. The nature of the sample preparation procedure does not limit throu

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141205

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe antibiotic streptomycin can be reliably quantitated in injectable pharmaceuticals by GC. The manipulations are not difficult, and total analysis time for duplicate samples is less than twenty minutes.Reaction of the drug with aqueous sodium hydroxide solution generates maltol, which is extracted into chloroform prior to silylation. The silyl ether of maltol is then assayed, using naphthalene as internal standard. Duplicate analyses of twenty pharmaceutical samples showed a relative standard deviation of ±1.3%

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141206

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

年代:1991

数据来源: WILEY

摘要:

AbstractSolid phase extraction with commercial C‐18 cartridges has been applied to the analysis of some well known chemical warfare agents in water samples. Different sample pretreatment and cartridge conditioning procedures, and different extraction solvents were tested to study the optimum conditions for efficient extraction and recovery of the compounds of interest. The eluates were analyzed with a two‐channel gas chromatograph equipped with an autosampler and a retention index monitoring system.The suitability of this technique for real samples is discussed: the rapid hydrolysis of many of the compounds studied and the poor recoveries of the polar degradation products are practical limitations of the met

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141207

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

年代:1991

数据来源: WILEY

摘要:

AbstractFactors influencing the stereoisomeric resolution of underivatized dipeptides and a representative tripeptide on Crownpak (CR) columns have been investigated. The elution order and relative retention suggest that a combination of chiral, steric, and hydrophobic interactions effects the extent of chiral recognition and the retention achieved during separations. Some dipeptides whose amine terminus is located three atoms from the asymmetric center (such as dipeptides ofD,L‐glycine) were resolved, but the elution order was the opposite of that expected for the type of Crownpak column used (CR(+)). Peptides containing hydrophobic substituents were strongly retained, but their retention times could be significantly reduced, and detectability improved, by use of gradient elution. Analysis of a commercial sample ofD,L‐leucine‐D,L‐alanine revealed the stereoisomers to be present in an unexpected quantitative ratio and demonstrated the utility of these separations for quality assurance and quantitative a

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141208

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

年代:1991

数据来源: WILEY

摘要:

AbstractNumerous reports have appeared on the determination of temperature programmed retention indexes in gas chromatography and although chromatographic variables should be completely consistent with published data if such indexes are to be of use, the reproduction of such rigorous parameters is quite difficult. This report presents an approximate method for using published values of temperature programmed retention indexes in isothermal chromatography.In general, the temperature dependence of the isothermal retention indexes of a number of compounds can be expressed as a series of oblique lines on a plot with retention index as the abscissa and temperature as the ordinate; the elution order of the compounds at a given, isothermal, temperature is then indicated by the points at which the compounds' oblique lines cut the horizontal line corresponding to the temperature of interest.In linear temperature programmed chromatography, the horizontal line representing isothermal operation becomes, to a first approximation, a sloping line with a gradient corresponding to the programming rate: this has been verified experimentally and may be valid over a wide range of temperatures. This line can be used to predict isothermal retention indexes for use in qualitative analysis.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141209

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe supercritical fluid extraction of polychlorinated dibenzo‐p‐dioxins from an incinerator fly ash sample has been investigated; supercritical nitrous oxide and its mixtures with methanol and toluene were employed as mobile phases.Recoveries of individual polychlorinated dibenzo‐p‐dioxins congeners were calculated from results of analysis of13C‐labeled dioxins by high resolution GC‐MS employing selected ion monitoring. The extraction procedure was compared with extraction in a Soxhlet apparatus, which is currently used as a standard method for removing chlorinated dibenzo‐p‐dioxins from fly ash samples: the results indicated that the time required for the extraction and clean‐up can be reduced from 24 to 2.5 hours/sample. Quantitative recovery of the chlorinated dibenzo‐p‐dioxins was achieved at μg/kg levels, the relative standard deviation was between 1.8 and 5.8%.The use of a virtually inert fluid such as pure nitrous oxide provides significant improvement over conventional extraction procedures because no solvent residue is left in

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141210

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

年代:1991

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240141211

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

年代:1991

数据来源: WILEY