Ladislav Soják

Environmental analysis of volatile organic compounds in water and sediment by gas chromatography

Considerable attention is still devoted to the analysis of volatile organic compounds (VOCs) owing to their occurrence in various fields and also harmful effects on health. The techniques used for their analysis are also manifold. The use of headspace techniques in the analysis of VOCs in various matrices has been well reviewed several times, but other techniques have been discussed only very briefly. The aim of this review is to give a brief survey of all techniques used in the environmental analysis of volatiles in water and sediment with emphasis on new trends and the applicability of these techniques in the analysis of water and sediment samples.

Capillary gas chromatography of alkylbenzenes. I. Some problems encountered with the precision of the retention indices of alkylbenzenes

A high-precision gas chromatographic system, in combination with high-resolution stainless-steel capillary columns and three stationary phases of different polarity, was used to study the separation and retention behaviour of 47 alkyl-benzenes up to C15, including all possible isomers between C6 and C10. The precision of the relative retention data is discussed in relation to the method of time measurement, non-ideality of the carrier gas, column temperature and ageing of the column. Taking into account these factors, the inter-laboratory agreement of the retention indices for aromatic hydrocarbons determined within and between laboratories can be improved considerably. Kovats retention indices and their temperature dependence were obtained with a precision corresponding to a standard deviation of about 0.1 index unit.

Gas chromatography analysis of benzene, toluene, ethylbenzene and xylenes using newly designed needle trap device in aqueous samples

A newly designed needle trap device with Carbopack X as a sorbent material is used for sampling, preconcentration and injection of volatile analytes benzene, toluene, ethylbenzene and xylenes (BTEX) into gas chromatograph. The closed system of stripping the analytes from water samples was used. An injection port with a modified metal liner was used to desorb analytes trapped in needle trap device. The main advantage of needle trap device consists in the simple methodology and easiness and rapidity of the analysis. Needle trap device is suitable for sampling in field. The experimental parameters as breakthrough volume of stripping gas, linearity, repeatability and limit of detection (LOD) and quantification (LOQ) were investigated. LOD ranges from 0.05 to 0.07 microgL(-1) and relative standard deviation ranges from 0.5% to 11.6% at concentrations 5 and 0.1 microgL(-1), respectively.

Gas chromatography of all C15C18 linear alkenes on capillary columns with very high resolution power

Abstract Conditions were studied for the separation of mixtures of all the 60 isomers of C 15 C 18 n -alkenes in the presence of the corresponding n -alkanes in highly efficient glass capillary columns ( N ≈ 0.5·10 6 effective plates for n -alkenes with k ≈ 3), coated with C 87 hydrocarbon, Apiezon L or Carbowax 20M as stationary phase. The separation of cis - and trans -isomers of n -alkenes is made possible at a sufficiently high column efficiency by the different dependences of their retentions on temperature. The separation of positional isomers of n -alkenes having even carbon numbers for the pairs with the most centrally situated double bonds can be achieved only by use of highly efficient columns with polar or non-polar stationary phases ( n req ≈ 10 6 plates). Correlations between the structure and increments H , δ I , d I /d T and Δ I , derived from retention indices of n -alkenes, were used for identification as they reflect the position of the double bond, the geometrical arrangement and the length of the carbon chain in various isomers. The so-called propyl effect was confirmed for trans -4-alkenes, disturbing the regularity of all correlations between structure and retention. The influence of adsorption of n -alkanes and n -alkenes at the polar phase-carrier gas interface on the retention characteristics is discussed. Reproducibility of retention indices of n -alkene isomers is a function of their capacity ratios (thickness of the stationary phase film in the column), decreases with polarity of the stationary phase and the isomer under analysis and with the difference between a reference standard and the n -alken ein question. These effects are so significant for the columns with Carbowax 20M that a different retention sequence was found for some n -alkene isomers in columns with relatively small differences in the thickness of the stationary phase.

Capillary gas chromatography of alkylbenzenes : II. Correlations between the structures and methylene group increments and differences in retention indices of isomers

Abstract The contribution to gas chromatographic retention behaviour of methylene group increments and differences in the retention indices (δ I ) of isomers of alkylbenzenes up to C 16 on squalane and acetyltri- n -butyl citrate was studied. The methylene group increments appear to vary over a wide range (60–100 i.u.) and depend on the magnitude, positions and relative lengths of the alkyl chains and on the number of carbon atoms. Anomalous retention behaviour of n -propylbenzene and its derivatives, except for molecules in which there are alkyl groups in both positions vicinal to the n -propyl group, was found. Hence, the correlations of I CH 2 in homologous series can serve as indicators of fine structural peculiarities of the molecules. The applicability of regularities in methylene group increments and δ I values, based on precise measurements of retention indices of low-molecular-weight alkylbenzenes, for confirmation of the identities of high-molecular-weight alkylbenzenes ( > C 10 ) is demonstrated.

Correlation of the boiling points of non-branched C9 and C10 olefins with the gas chromatographic retention indices

Abstract A correlation was made between the boiling points of fourteen non-branched nonenes and decenes and the retention indices, and also a comparison of the results obtained by known methods of calculation with the available tabulated data. The gas chromatographic measurements were carried out on a 200-m long capillary column (stainless steel) coated with squalane at 86, 100 and 115° and permitted boiling points to be determined with a reproducibility of ± 0.1°. Substantial deviations were found from the Kovats rule δI ≈ kp δTb for the behaviour of isomeric hydrocarbons on a non-polar stationary phase. In the case of the olefins studied, the proportionality constant, for which a value of approximately 5 is stated in the literature, fell within the range 1.8–13.9 on squalane. The correction factor fc used for the calculation of IB by M atukuma is constant only in the case of trans-alkenes, whereas for cis-alkenes and I -alkenes it is dependent on the number of carbon atoms in the olefin molecule.

Topological analysis of the behaviour of linear alkenes up to tetradecenes in gas-liquid chromatography on squalane

Abstract DARC topological analysis (DTA) has been applied to Kovats retention indices for a series of 84 linear alkenes up to tetradecenes studied by gas-liquid chromatography on squalane at 100 °C. The topology-information diagram gives information at the skeletal carbon atom level of the alkene molecules. Very small structural effects are detected and discussed on a statistical basis. This set of n -alkenes constitutes a good model for testing the interpretative and physico-chemical potentialities of DTA in order to establish a set of precise reference data for higher n -olefins of petrochemical interest.

Capillary gas chromatography of alkylbenzenes : III. Correlations between the temperature and pressure coefficients of the retention index and structure

Abstract Correlations between the structures of alkylbenzenes and the temperature and pressure coefficients of their retention indices were studied, in addition to their dependence on the polarity of the stationary phase, the column inlet pressure and the nature of the carrier gas. The temperature coefficients (d I /d T ) vary within relatively wide limits and reflect fine-structural differences in the alkylbenzenes. They are inversely proportional to the symmetry of the molecules and the size of their alkyl groups. The d I /d T values are about one order of magnitude larger on the highly polar 1,2,3-triscyanoethoxypropane (TCEP) than on squalane. Although the data on the pressure coefficients on TCEP are limited, there are indications that correlations similar to the d I /d T —structure correlations also hold. Under the same experimental conditions, a change in the carrier gas from hydrogen the nitrogen at a constant inlet pressure (1 atm) has an effect on the retention index of alkylbenzenes of the same order as that resulting from an increase in the inlet pressure of nitrogen of 1 atm The possible application of d I /d P values for identification purposes in combination with gas chromatography at higher pressures is discussed.

Hochleistungs-gaschromatograpahie an flüssigkristallglaskapillaren☆

Abstract High-performance glass capillary columns with 5- n -heptyl-2-(4- n -nonyloxyphenyl)-pyrimidine were applied for separations of isomeric alkylbenzenes and n -alkens in smectic C and smectic A also in the nematic, isotropic and crystalline range. Structure-retentio correlations were discussed from calculated retention indices and their dependence on temperature. The smectic modifications shows better separations in comparison with previous methods.

Anomalies in the gas chromatographic behaviour of substances facilitating a ring conformation through their propyl group

Abstract The applicability of precise gas chromatogaphic measurements has been demonstrated for the identification of very fine structural features of compounds. On the basis of the gas chromatographic behaviour of five classes of unsaturated hydrocarbons and four classes of compounds containing hetero-atoms, it is concluded that retention anomalies are to be expected for compounds with molecular structures that make it possible to form a ring conformation of the propyl group with the π-electron system of the remainder of the molecule and that this phenomenon is a common feature of the compounds with such structures.