A novel cryogenic modulator was constructed for comprehensive two-dimensional gas chromatography (GC x GC). The modulator is based on two-step cryogenic trapping with CO2 and thermal desorption with electric heating. The GC x GC system included a nonpolar first-dimension column and two semipolar second-dimension columns, one connected to a flame ionization detector and the other one to a electron capture detector. A Matlab-based program, which allowed determination of peak heights and volumes, was written for the data analysis. The GC x GC system was applied for the analysis of polyaromatic hydrocarbons and polychlorinated biphenyls. The functioning of the modulator and the quantitativity of the method were studied with both peak volumes and peak heights from a three-dimensional plot. The separate peak areas from the modulated chromatogram were calculated as a comparison. The quantitative results were compared with those obtained with the same system but without the thermal modulation. The method was found to be repeatable and linear with use of peak volumes as well as peak heights. There was also good agreement with the results obtained by integration of separate peak areas. The developed GC x GC method was applied to the analysis of a Soxhlet extract of a certified sediment sample. The results were compared with the certified values.

No abstract

No abstract

No abstract

Peak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate-co-N-vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm(-1) were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.