Jiří Vejrosta

Air/water partition coefficients for normal alkanes (n-pentane to n-nonane)

Abstract Consistent values of the air/water partition coefficient for n -pentane, n -hexane, n -heptane, n -octane and n -nonane have been measured in the temperature range 15–35°C. All of the results may be summarised by an equation derived on the basis of thermodynamic principles. The constants of this equation have been determined by least-squares regression. The solubilities of hydrocarbons in water as well as thermodynamic quantities relating to the solvation process can be predicted using the equation.

Direct supercritical fluid extraction of water-based matrices

Abstract A short review on direct supercritical fluid extraction (SFE) of organic compounds from aqueous samples is presented. The SFE methodology of water samples is conceptually different from that of solid matrices, and a relatively small number of papers on this subject has been published. As the most promising appears continual SFE of water samples with pure CO2.

Method for the preparation of continuous streams of gaseous calibration mixtures with defined contents of standard substances

Abstract A method for the preparation of gaseous calibration mixtures with defined contents of standard substances is described. An accurately controlled stream of gas ( e.g. , nitrogen) is drawn at a low flow-rate through a thermostated container filled with a chromatographic support impregnated with the standard substance, thus generating a continuous stream of saturated vapour of the substance. This stream is diluted in a mixing chamber with a large stream of pure gas, and a small fraction of the dilute mixture, separated by means of a splitter, is again diluted with a large stream of pure gas in another mixing chamber. In this two-stage dilution procedure it is possible to prepare mixture containing standard substances at parts per billion concentrations with an error of about 4%. Mixtures containing several standards are obtained through use of a separate saturator for each standard; the concentration ratio of two standard substances can be set to within the range 1:1 to 1:10 6 .

Pressurised liquid extraction of ketones of polycyclic aromatic hydrocarbons from soil.

Pressurised liquid extraction (PLE) was used in the extraction of three ketones of polycyclic aromatic hydrocarbons from the sample of a soil highly contaminated with polycyclic polyaromatic compounds. The choice of solvent was the only factor that considerably influenced the extraction efficiency of PLE under the conditions recommended in Method 3545A promulgated by the United States Environmental Protection Agency. The dichloromethane-ethanol solvent mixture was found to be the most efficient solvent. PLE using this mixture provided better recoveries of all analysed ketones relative to Soxhlet extraction.

Correlation of gas chromatographic specific retention volumes of homologous compounds with temperatures and methylene number

Abstract The specific retention volumes of homologous compounds can be expressed by log V g = p + q / T + nr + s , where n is the number of methylene groups in the solute molecule, T is the absolute temperature and p, q, r and s are constants related to the thermodynamic properties of the chromatographic system. Generally, the specific retention volumes measured for four homologues at different temperatures are sufficient for determining the constants of the equation. The accuracy of the V g values calculated for given n,T data by the equation is commensurate with the precision of replicate determinations of the V g value of a given compound on a given instrument.

Systematic errors occurring with the use of gas-sampling loop injectors in gas chromatography

Abstract Gas sampling valves, involving a fixed-volume loop, are widely used as injection devices in gas chromatography. It is shown that adsorption of the substance under consideration on the inner wall of the loop tube will cause a systematic error in the injected amount. This effect can in many practical cases be significant as is shown by experiments and theoretical calculations.

Spurious adsorption effects in headspace-gas determination of hydrocarbons in water

Abstract The adsorption of benzene, hexane, heptane and octane at the phase interfaces in a gas—water system representing those used in static headspace-gas trace analysis was investigated. The apparent bulk water—gas distribution constants, calculated from the known total amounts of the model solutes adn their gas-phase contents determined analytically, true builk water—gas distribution constants, determined directly by analysis of both the aqueous and gaseous phases, and water surface—gas adsorption distribution constants, calculated from the solute mass balance, are presented and discussed. Adsorption phenomena were shown to play a signficant role with alkanes in gas—aqueous liquid systems.

Interference effects in trapping trace components from gases on chromatographic sorbents : Sorption of benzene in the presence of o-xylene

Abstract The sorption isotherms of benzene in the presence of o-xylene as a co-sorbate were measured in various chromatographic sorbent—nitrogen systems at 35°C. The benzene gas-phase concentration was kept at 0.5 ppm while that of o-xylene was varied within about 0.025–25 ppm. With Tenax GC, Porapak P and Porapak Q as sorbents the partition coefficients of benzene were substantially decreased due to the presence even of about 0.01 ppm o-xylene in the gaseous phase. With Apiezon K and QF-1 liquid sorbents the partition coefficients of benzene remained practically constant up to about 2.5 ppm of o-xylene in the gaseous phase.

A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems

Vejrosta, J., Novak, J. and Jonsson, J.A., 1982. A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems. Fluid Phase Equilibria, 8: 25–35. A method has been developed for measuring the partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems, based on the direct analysis of both phases. A gas mixture containing a known proportion of a volatile compound is drawn through the liquid (water) until equilibrium is established. A defined volume of the liquid phase is then withdrawn through a porous-polymer trap while maintaining the system at equilibrium. The residual water in the trap is then expelled by a stream of nitrogen gas, and the deposit remaining is thermally desorbed and analyzed by gas chromatography. This approach, together with an experimental technique for producing gas mixtures containing an accurately known concentration of hydrocarbon at low values, makes it possible to determine accurately the partition coefficients of low-solubility compounds, such as for hydrocarbons in aqueous systems, at very low solute concentrations in the system. The method has been verified by measuring the partition coefficient of hexane between the gas and liquid phases of an aqueous system at various concentrations and temperatures.

Separation of alkali metal carboxybenzenesulphonates and their 2-hydroxyethyl esters on sephadex LH-20 gel

Abstract Mixtures of alkali metal carboxybenzenesulphonates and their 2-hydroxyethyl and bis(2-hydroxyethyl) esters, obtained by esterification of the carboxybenzene-sulphonates with ethylene glycol at elevated temperatures, were readily separated by chromatography on Sephadex LH-20 gel at pH 8.5 by using potassium dihydrogen orthophosphate-disodium hydrogen orthophosphate buffer as eluent.