摘要:

AbstractA π‐basic, brush‐type chiral stationary phase (CSP) derived from (S)‐N‐(1‐naphthyl)leucine undecenyl ester has been shown to effectively separate the enantiomers of a broad array of π‐acidic analytes. Armed with a mechanistic hypothesis as to how this CSP differentiates between the enantiomers of π‐acidic derivatives of α‐amino acids, the structure of this CSP was modified in a series of steps, each intended to enhance the enantioselectivity of the CSP. Specifically, brush‐type CSPs were prepared fromN‐(5‐naphthyl)leucine di‐n‐propyl amide and fromN‐(5‐acenaphthyl)leucine di‐n‐propyl amide. The latter selector was also incorporated into a polysiloxane, then coated and bonded to silica. The rationale for each of the structural changes, and its effect on the enantioselectiv

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170902

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

年代:1994

数据来源: WILEY

摘要:

AbstractLevels of linear alkylbenzenesulfonate (LAS) detergents have been measured in Anzali lagoon water sampled at fourteen stations. All samples were extracted with octadecyl‐bonded silica membrane disks. Extraction efficiency, maximum capacity, and the effect of the solvent used to extract the LAS from the membrane disks were evaluated. Extraction efficiencies>95% were obtained by elution of the disks with minimal amounts of solvent. It was demonstrated that membrane disk extraction introduced less error into analytical results than liquid – liquid extraction. Quantitative determination of total LAS levels and measurement of the distribution of LAS homologs with C10C13alkyl chains were performed by high resolution gas chromatography with flame ionization detection after derivatization of the detergents with sulfonyl chloride. The total level of LAS ranged from 0.01 to 0.8

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170903

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

年代:1994

数据来源: WILEY

摘要:

AbstractRacemic amino alcohols have been separated as perfluoroacylated derivatives by gas chromatography using either improved Chirasil‐Val or heptakis(2,6‐di‐O‐methyl‐3‐O‐pentyl)‐β‐cyclodextrin as stationary phase. Using Chirasil‐Val all the amino alcohols investigated were separated to baseline (α values between 1.03 and 1.08) whereas only a few amino alcohols were resolved on the modified cyclodextrin column. The enantioselectivity obtained on the latter phase was, however, significantly higher.The separations were performed as trifluoroacetyl, pentafluoropropionyl, and heptafluorobutyryl derivatives and the chiral discrimination observed for the different derivatives was significantly different for both stationary phases.In oder to obtain a better understanding of the separation mechanism, theGibbs‐Helmholtzparameters Δ(R,S)ΔH° and Δ(R,S)ΔS° were determined. The most extraordinary result was obtained for the trifluoroacetyl derivative ofallo‐threoninol. In addition to the order of elution of the enantiomers being the opposite of that for the other compounds, the separation seems to be entropy controlled (the sign Δ(R,S)ΔH° is positive),i.e.the separati

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170904

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe dependence of the limonene content of lemon (Citrus volkameriana) peel oil on the degree of ripeness of the fruit has been studied by using steam distillation and cold pressing to extract the oils from lemon fruit peel at different stages of maturation (green, greenish‐yellow, and yellow‐orange peel coloration). Samples of essential oils were analyzed by high resolution GC and GC‐MS, using tetradecane as internal standard for quantitation. Forty components were detected; thirty eight were positively identified by comparison of their mass spectra (El, 70 eV) andKovátsretention indexes (determined using a non‐logarithmic scale on capillary columns coated with both polar (DB‐Wax) and non‐polar (DB‐1) stationary phases) with those of standards and with data reported in the literature. The limonene concentration reached a maximum level of 79.4% when the fruit was in the intermediate maturation stage characterized by greenish‐y

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170905

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

年代:1994

数据来源: WILEY

摘要:

AbstractA GC autosampler designed for liquid injection was modified for static headspace sampling. The modification was very simple and involved replacement of the standard 10‐μL syringe with a 100‐μL gas‐tight syringe. Liquid samples (0.2‐1.0 mL) were placed in 2‐mL vials, normally used for liquid sampling and an aliquot of the head‐space above the liquid was withdrawn and injected into the GC. All parts of the sampling system were at ambient temperature. The system was found to be useful for several applications. Among those discussed in this paper are determination of ethanol in the blood or urine of individuals suspected of driving while intoxicated, residual organic solvents in pharmaceuticals, and screening of effluent waters from industrial plants for

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170906

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

年代:1994

数据来源: WILEY

摘要:

AbstractA home‐made temperature control unit has been developed for a commercial capillary electrophoresis apparatus, the Waters Quanta 4000. The effect of the unit on the absolute migration times and peak areas of nine β‐blockers is described. It was found that this homemade temperature control unit considerably (≥ 100 %) improved the repeatability of the sepa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170907

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

年代:1994

数据来源: WILEY

摘要:

AbstractA method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC‐MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2‐ and 3‐dechloroethyliphosphamide, 4‐ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3‐oxazolidine‐2‐one.The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield ofca50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3‐oxazolidine‐2‐one were isolated with high yield by liquid extraction with ethyl acetate at pH 10.Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per m

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170908

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

年代:1994

数据来源: WILEY

摘要:

AbstractA modification of a procedure byHage[1] is proposed for the gas chromatographic evaluation of the content of free medium‐chain fatty acids and related ethyl esters in beer. The method involves extraction of free fatty acids and ethyl esters by SPE using C18bonded phase columns, derivatization of free fatty acids and related ethyl esters with diazomethane, and GC analysis using an SP‐2340 capillary column. The results obtained have shown the method to be rapid and highly reproducible. The technique has been compared with other methods used for determination of free fatty ac

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170909

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

年代:1994

数据来源: WILEY

摘要:

AbstractSDS (sodium dodecyl sulfate) has been quantitatively determined by capillary zone electrophoresis using a fused silica capillary and a 5 mMdihydroxybenzoic acid / sodium hydroxide buffer in 5% methanol solution at a pH of 8.1. The ion was detected by indirect UV absorption at 250 nm. Detection range was from 0.8 to 50 mg SDS/L. This rapid method requiring only small sample volumes was developed in support of an aquatic toxicology study in a simulated stream water and is applicable to waters containing common inorganic ions.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240170910

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.1240170912

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

年代:1994

数据来源: WILEY