ISSN:0935-6304    

DOI:10.1002/jhrc.1240120302

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

年代:1989

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120303

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

年代:1989

数据来源: WILEY

摘要:

AbstractA high temperature gas chromatograph has been developed which is capable of operating at column oven temperatures up to 500°C. In addition, the detector can operate at temperatures up to 500°C, and the injector up to 450°C. The injector on this instrument is a temperature programmable direct injector, designed specifically to introduce labile or high molecular weight samples into the GC without molecular weight discrimination. The design of this GC and injector will be described, and high temperature applications will be discuss

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120304

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

年代:1989

数据来源: WILEY

摘要:

AbstractTwo methods for sampling and concentration of volatile organic compounds are reported. In the first method, traps coated with a very thick film (ca.100 μm) of cross‐linked silicone stationary phase are employed. Such thick films can be prepared with a modified dynamic coating procedure, which is briefly described. The low phase ratio traps can be utilized for enrichment of volatiles from gaseous as well as aqueous matrices.The second technique is based on chromatographic evaporation of a solvent in a capillary tube, where the process is sustained by a repeated sample injection and a cyclic flow reversal. In this way, large solvent volumes can be handled by a small volume system. Under optimal conditions, when using a solvent barrier, quantitative recovery is possible even for compounds of comparatively high volatility. Another important application of the technique is extraction of trace components from gases such as headspace samples, polluted air,e

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120305

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

年代:1989

数据来源: WILEY

摘要:

AbstractSeparations of high efficiency and/or speed can be achieved in capillary GC by capillary columns of lower internal diameter (<50 μm). Sampling techniques for the analytical application of narrow bore fused silica columns have been evaluated with regard to quantitation. On‐column injection cannot be applied. Therefore liquid samples have to be vaporized in external devices before they enter the chromatographic system. Sample introduction by syringe with subsequent splitting must and can be applied but requires special syringes with perfect piston sealing because of the high inlet pressures needed even with hydrogen as carrier gas. For general analytical applications, valve systems should be developed to eliminate both the syringe and the septum from instrumental GC set‐up's.In SFC using either narrow bore capillary or packed microbore columns, time‐controlled valve sampling with partial displacement of the sample from the loop seems to be an adequate technique because of the very high inlet pressures involved. Splitting in combination with valve operation can also be applied in capillary SFC at least to samples of good solubility in the mobile phase. A disadvantage of splitting in SFC is that another restriction for the adjustment of the split flow is nec

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120306

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

年代:1989

数据来源: WILEY

摘要:

AbstractA model utilizing the extended Golay‐Giddings equation, with an added term that expresses the instrumental contributions to the plate height, has been tested and found to accurately predict the chromatograph's output for a given set of operating conditions. The model forms the basis of a computer program that will recommend the length of column (of a specified inside diameter and film thickness) to be used (at a given temperature and input pressure) to obtain a minimum time analysis of the most difficult to separate pair of the mixture. Alternative solutions are available that specify the length of column, operating pressure, and the maximum permissible sample size required to provide a minimum analysis time for a system with specified minimum detection limit

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120307

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

年代:1989

数据来源: WILEY

摘要:

AbstractOxo‐ and hydroxycarboxylic acids as metabolites of valine, leucine, and isoleucine and of ketogenesis are simultaneously quantitated in the form of their methyl esters and methyl esters/O‐methyloximes by gas chromatography using internal and external standards. Normal values for the urinary excretions of the amino acid metabolites are between 3 ± 2 μmol/24 h (mean value ± standard deviation) for 2‐oxoisocaproic acid and 122 ± 58 μmol/24 h for 3‐hydroxyisobutyric acid. In diabetic ketoacidosis the values are increased by a fa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120308

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

年代:1989

数据来源: WILEY

摘要:

AbstractAn elastic inner wall coating in the fused silica capillaries used for Micro‐LC (LC on packed fused silica capillary columns) stabilizes the packed bed and thus increases column efficiency and life expectancy. Probably the particles of packing material are partly forced into the elastic polymer layer which thus holds the packing in position. Bonded polymers of very different chemical polarity can be used with equally good results. Variation of the coating layer thickness shows that there is an optimum value around 0.3 μm. A discussion of various wall effects in LC columns is presented. The i.d. of the columns is a most important parameter in this respe

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120309

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe retention characteristics of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) have been examined in liquid chromatography on a microcapillary column packed with cellulose acetate. Particulate and fibrous cellulose acetate were used as the stationary phase. Fibrous cellulose diacetate was found to be of use as an alternative stationary phase for liquid chromatography, although the separation efficiency was low. The retention characteristics for planar PAHs were linearly correlated with the size of the molecules, but the retention behavior for alkylbenzenes and nonplanar PAHs was affected by exclusion. The retention order was strongly influenced by the addition of dimethylformamide or water to methanol in the mobile phase. The results suggested that the retention behavior is influenced by a slight change in the polymer matrix of cellulose acetate.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120310

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

年代:1989

数据来源: WILEY

摘要:

AbstractFormation of volatiles in onion varieties, aging of coffee, and the quality of birch syrup were studied by using near room temperature headspace GC‐MS analysis. Accurate volumes (1–500 mL) of the gaseous samples were introduced into the capillary column either by a syringe or by sucking with a pump. The standard deviation of the contents was typically 1‐7% depending on the foodstuff and the compound. The ratio of 2,3‐butanedione to 2‐methylfuran decreased during the storage of coffee and was a typical measure of aging. Analysis of even the very polar 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone in the headspace of birch syrup was possible. The distribution patterns of the sulfur‐containing volatiles generated by crushed onions were close to each other in different varieties. The rate of the total formation of the compounds varied from

ISSN:0935-6304    

DOI:10.1002/jhrc.1240120311

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

年代:1989

数据来源: WILEY