Study of peak profiles in nonlinear gas chromatography: Application to the peak distortions observed with overloaded capillary columns

The elution profiles observed with overloaded capillary columns are well described by a four-parameter theoretical model derived from the basic mass balance equations which relies on an expansion of the partition isotherm to the second term and takes the sorption effect into account. The reliability of the model is demonstrated by the fact that the peak leaning coefficient obtained from a least squares fit of the model to the experimental peak is in good agreement with that obtained from the variation of peak height with retention time at peak maximum. The coefficeint of apparent axial dispersion is independent of sample size and can be used to characterize the plate height at zero concentration of an overloaded capillary column.     

On-line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography

The introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off-line experiments requiring collection and reinjection of the separate fractions or by on-line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on-line to a capillary gas chromatograph. The liquid chromatograph (so designed) can act as a highly efficient clean-up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean-up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.     

Automated determination of nifedipine in human plasma by capillary gas chromatography with electron capture detection

A rapid, sensitive, and reliable method for the determination of nifedipine in human plasma is described. Using a single-step solvent extraction and capillary gas chromatography combined with electron capture detection, an assay sensitivity of 2 ng/ml is achieved routinely using 0.5 ml of plasma. Intact nifedipine is quantitated and separated from its nitroso- and nitropyridine-derivatives. The suitability of the assay for pharmacokinetic studies is illustrated.     

An improved method for steroid profile analysis using capillary gas chromatography

Summary Steroid conjugates are hydrolysed enzymatically using β-glucuronidase after extraction from urine using a solid phase extraction cartridge. After hydrolysis the free steroids are removed from the matrix, again utilising solid phase extraction. Derivatisation of the free hydroxyl groups using Hydrox-Sil AQ produces the respective TMS ethers which are extracted into hexane, in which solvent they are stable for many days. Capillary GC analysis with flame ionisation detection produces a profile of the steroids present in the sample. This technique is suitable for following changes in the urinary excretion profiles of patients undergoing investigation for a variety of steroid production-related diseases.     

Analysis of mutagenic amino acid pyrolyzates with a fused silica capillary column

In this study, application of a fused silica capillary column for analysis of major mutagenic heterocyclic compounds found in cooked foods was investigated.     

Dynamic headspace capillary gas chromatography: A versatile analytical technique

The applicability of dynamic headspace analyses for viscous liquids and solid samples is demonstrated. Some comments on the usefulness of this technique for quantifying volatiles in polymeric matrices are made.     

Enzyme activity determination by radio gas chromatography on capillary columns

Androgen 5α-reductase from the foreskin of 48 boys in prepubertal age was analyzed by evaluation of the apparent K_m-and V_max- values after tissue incubation. Reaction rates were calculated after determination of specific radioactivity of distinct metabolites, by comparison to the radioactivity of the precursor. Reaction products were separated by radio gas chromatography on capillary columns. The chromatography system was based on multicolumn equipment with column switching facilities and a variable splitter at the outlet of the separation column. A radioactivity monitor (gas proportional counter) was used for measurement of radioactivity in the column effluents. An electron capture detector was used for mass detection of steroid acyl derivatives.     

Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Enantiomer separation of 2-halocarboxylic acid esters by chiral complexation gas chromatography

The enantiomer separation of 2-halocarboxylic acid esters on two chiral nickel(II) bis-((perfluoroacyl)terpeneketonates) by complexation gas chromatography is described. The quantitative entiomer separation of branched 2-halocarboxylic acid esters is achieved with nickel (II) bis (3-(heptafluorobutanoyl)(1R, 2S)-pinan-4-onate) 1 while unbranched 2-halocarboxylic acid esters are preferably separated on nickel(II) bis(3-(heptafluorobutanoyl)-(1S)-10-methylenecamphorate) 2. The metal chelates 1 and 2 are accessible in both enantiomeric forms allowing the determination of the enantiomeric excess (ee) effective and reliable.     

Quantitative gas chromatography using a new automated derivatizer

In the gas chromatographic analysis of complex biological samples, the most time-consuming and error-prone steps are the pretreatment required for isolation and purification of the compounds of interest and, for most analytes, the derivatization to chemically and thermally stable compounds with high volatility. These wet-chemical steps are usually carried out manually, and for routine analysis of large numbers of samples they are often rate-limiting. A dedicated automated derivatizer has been constructed, the employment of which significantly reduces the time required for manual labor and increases the reproducibility of derivatization and hence the accuracy of analysis.     

The autoderivatization of 4-ketocyclophosphamide during capillary gas chromatography

The selectivity of a capillary gas chromatographic assay for the anti-neoplastic and immunosuppressive agent cyclophosphamide (CPA) towards one of its naturally occurring metabolites, i.e. 4-ketocyclophosphamide (4-keto CPA), has been studied. Mass spectrometry studies showed that a cyclization product of 4-keto-CPA can form using the same chromatographic conditions as those under which CPA was determined. However, the amount produced is relatively small (less than 10%) compared with the percentage produced from CPA. Furthermore, both cyclization products, formed by loss of HCI and intraalkylation of the parent compounds, can be separated well under suitable chromatographic conditions.     

Capillary gas chromatography of amino acids as their tert-butyldimethylsilyl derivatives in the analysis of serum amino acids in metabolic diseases

Reaction of amino acids with N-methyl-N-(tert-butyldimethylsilyl)trifluoroaceamide (MTbSTFA) in acetonitrile affords good yields of amino acid derivatives with excellent gas chromatographic and mass spectrometric properties. The single-step derivatization procedure is highly reproducible. The TBDMS amino acids are stable at room temperature for at least three days. Only a single peak is observed for each amino acid. The procedure allows simultaneous analysis of asparagine and glutamine together with other serum amino acids. Separation is achieved on a borosilicate glass capillary coated with OV-1. The mass spectra of the TBDMS amino acids possess characteristic diagnostic ions. These properties were used in the sensitive detection by GC-MS and SIM-GC-MS of GABA and pipecolic acid in the serum of a newborn suspected of a Zellweger-type syndrome, which could not be detected by other methods.     

Glass capillary gas chromatography of amino acid enantiomers

Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable.     

Optimization of capillary parameters for gas chromatography

An HETP equation for the capillary column is developed that takes into account the dependence of gaseous diffusion on pressure, the compressibility of the mobile phase, together with the unique relationship between mobile phase velocity, and the resistance to mass transfer in the stationary phase. The equation is used to develop a procedure for column optimization and expressions are derived that allow the optimum column radius and optimum column length to be calculated for a given fixed inlet pressure. It is shown that fast, simple separations are optimally achieved using relatively short small diameter columns. Conversely, optimum performance for the separation of complex mixtures requiring higher efficiencies requires the use of long columns with relatively large diameters.     

Sample introduction in high speed capillary gas chromatography; input band width and detection limits

The speed of analysis in capillary gas chromatography can be substantially increased by reduction of the column inner diameter. However, special demands are then posed upon instrumental design. In particular, the sampling system is highly critical because it has to be capable of delivering extremely small injection band widths which must be compatible with the column inside diameter. This study focuses on the evaluation of two potentially suitable sample introduction systems with respect to input band width and detection limits and their compatibility with small bore (≦ 100 μm) columns in capillary gas chromatography. One of them allows liquid on-column injection, based on liquid splitting, of only a few nl onto small bore (≦ 100 ?m) fused silica columns. For gases, input band widths as low as 1 ms are obtained with this system. The other one is part of a miniaturized gas chromatograph with extremely low dead volume interfaces and detector volumes. It allows input band widths for gases of a few ms. Without any preconcentration ppm concentrations are measured in gaseous samples with a 80 ?m thick film capillary column. It will be shown that a further reduction of the minimum detectable amount and analysis time is possible with this equipment.