Harmonisation of coupled calibration curves to reduce correlated effects in the analysis of natural gas by gas chromatography

Quantitative analysis of natural gas depends on the calibration of a gas chromatograph with certified gas mixtures and the determination of a response relationship for each species by regression analysis. The uncertainty in this calibration is dominated by variations in the amount of the sample used for each analysis that are strongly correlated for all species measured in the same run. The "harmonisation" method described here minimises the influence of these correlations on the calculated calibration curves and leads to a reduction in the root-mean-square residual deviations from the fitted curve of a factor between 2 and 5. Consequently, it removes the requirement for each run in the calibration procedure to be carried out under the same external conditions, and opens the possibility that new data, measured under different environmental or instrumental conditions, can be appended to an existing calibration database.     

Analysis of barbiturates by gas chromatography

This review surveys the evolution of gas chromatographyic procedures for the quantification of barbiturates as either the free acids or their derivatives obtained by direct and on-column reactions. Among the aspects discussed, some emphasis is placed on recognized and other sources of interference encountered during analyses.     

Rapid screening of natural products by high-resolution high-temperature gas chromatography

The crude ethanol extracts from the leaves of three Croton hemiargyrus hemiargyreus plants are fractionated by thin-layer chromatography, yielding five fractions. The fractions and the crude extract are analyzed by high-temperature high-resolution gas chromatography coupled with mass spectrometry (HT-HRGC-MS). Several natural products, including thermolabile components, can be characterized directly in the samples, such as alkaloids, terpenes, flavonoids, acids, alcohols, etc. The cold on-column technique proves to be appropriate for the injection of these thermolabile compounds. HT-HRGC-MS is shown to be a valuable tool and an alternative technique to classical phytochemical procedures for the simple and fast routine analysis of natural products in crude extracts.     

Analysis of polychlorinated biphenyl mixtures by gas chromatography

The data published during the recent 10–15 years on the conditions of gas chromatographic separation (columns, temperature modes, and detection methods), identification, and determination of the components of polychlorinated biphenyl technical mixtures are summarized. Special attention is paid to mass-spectrometric detection.     

Analysis of Fischer-Tropsch by-product waters by gas chromatography

This paper describes a quantitative technique for the determination of organic constituents in Fischer-Tropsch by-product waters. Temperature-programmed gas chromatography on derivatized bonded polar capillary columns provides the required separation that permits reliable quantitation of individual compounds. A preliminary combined gas chromatographic–mass spectrometric survey to identify the components present in Fischer-Tropsch by-product waters is presented. The elution order of 58 identified components is tabulated. Components identified in a typical Fischer-Tropsch by-product water include C₁–C₉ linear and branched alcohols, C₃? C₈ ketones, C₂? C₆ carboxylic acids, and C₂? C₄ linear aldehydes.     

Rate study of reduction of 2-heptanone with samarium iodide by gas chromatography

This article describes a newly developed method of gas chromatography (GC) for the rate study of the reduction of organic compounds by samarium iodide. Solvent extraction was used to reduce the interference of GC analysis by inorganic species. Adequate recoveries ranged from 88.3 to 94.5 % and good linearity ranging from 0.1 to 2.1 mM was determined. An internal standard, decane, was used to enhance the precision of this test. The coefficient variations of intra-day and inter-day ranged from 0.22 to 3.00%. The stability of the reacted sample was also assessed. In addition, the reaction rates of the reduction of 2-heptanone by samarium iodide in the presence of hexamethylphosphoramide were examined. The results presented hererin demonstrate the utility of this method in kinetic studies.     

Analysis of seven chlorobiphenyl congeners by multidimensional gas chromatography

Chlorobiphenyl congeners (CBs) are used as indicator compounds in analysis performed to determine whether or not PCB concentrations in food products, waste mineral oil, and environmental samples comply with the maximum levels permitted by legislation. Seven of these compounds have been checked for coelution with other CB congeners by means of a multidimensional gas chromatographic method utilizing a combination of two narrow bore columns, one coated with a conventional non-polar stationary phase and the other with a liquid crystalline (smectic) stationary phase. Peaks of the relevant CBs have been transferred, by heart cutting, from the non-polar column to the liquid crystal column, on which unambiguous separation from possible coeluting CB congeners was obtained. It has been shown that if the seven congeners are analyzed solely on a single, non-polar capillary column the results obtained for two of them may be affected by coelution of other compounds.     

Analysis of D-penicillamine by gas chromatography utilizing nitrogen--phosphorus detection

A method is presented for the analysis of the "orphan" drug D-penicillamine (D-Pa), which is used for the treatment of the inherited rare copper metabolism dysfunction known as Wilson's disease, by assaying a derivative of the compound by gas chromatography employing a rubidium sensitized nitrogen--phosphorus detector. Analytical procedures are described for the analyses of residues of D-Pa X HCl salt in animal feed and for the analyses of the salt or free base from aqueous solutions by utilizing a single-step double derivatization with diazomethane--acetone. Stability data for D-Pa X HCl in animal feed and for the free base in water are presented. An ancillary fluorescence derivatization procedure for the analysis of D-Pa in water is also reported.     

Analysis of trace components in gases by gas chromatography

Summary Relationships are derived describing how the detection limit of a chromatographic system depends on the minimum detectable limit of the detector and the chromatographic parameters such as column length, efficiency, carrier gas flow rate and the capacity factor. Performance data of detectors developed in the last 25 years at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences are given and a few selected application examples are listed. These include trace analysis by preconcentration and by direct analysis and the utilization of multidimensional gas chromatography with two columns, two detectors, a 12-port valve, and a catalytic conversion reactor.     

Analysis of legume oligosaccharides by high-resolution gas chromatography.

The suitability of high-resolution gas chromatography (HGRC) for the analysis of the raffinose family oligosaccharides (raffinose, stachyose, verbascose) was investigated. Aqueous methanol (80%) extracts of pea flour were dried and derivatized with either trimethylimidazole or N-methyl-bis(trifluoroacetamide). Separation of the sugar derivatives was achieved utilizing a 10-m DB5-60W capillary column. The effects of carrier gas (He) flow-rate and split ratio on resolution and reproducibility were studied. HRGC analysis was characterized by excellent resolution and satisfactory reproducibility, and proved to be a rapid, sensitive method for quantitation of oligosaccharides in pea flours.     

Analysis of plasma-polymerized hydrocarbons by pyrolysis/gas chromatography

Plasma-polymerized oils, films and powders obtained from ethylene, acetylene, butadiene, and benzene were characterized by flash pyrolysis and gas chromatography (P/GC). None of the pyrograms resembled those of commercial polyethylene, polybutadiene, or polystyrene. Each of the plasma-polymer pyrograms did exhibit essentially the same fragments up to C₈, albeit in a different distribution, indicating that all samples are structurally similar. Analysis of the P/GC data shows these materials to contain a random arrangement of side chains, crosslinks, double bonds, and aromatic structures. Changes in the fragment distribution were obvious when the sample was a powder, solid film, or oily film produced from the same monomer. It was shown that powder products generally have a higher concentration of branches and/or crosslinks than the oil or film products. There are also differences in the pyrograms of products of the same form derived from dissimilar monomers. The results obtained from P/GC generally support those derived from infrared or NMR measurements performed earlier.