Sorption of volatile organics from water using an open-tubular, wall-coated capillary column

Abstract

Passing an aqueous solution containing volatile organic compounds through a gas chromatography (GC) capillary column allows the extraction of the organic components onto the column stationary phase. If a sufficient volume of the aqueous solution passes through the capillary, the extraction reaches equilibrium. Studies using BTEX (benzene, toluene, ethylbenzene, xylene compounds) in water, with collection and GC-flame ionization detection analysis of 100 μL fractions of the aqueous solution collected from the capillary, enables a sorption profile to be generated. Boltzmann curves may be fitted to the sorption profile data and mathematical integration of the curves allows the estimation of the amount of solute sorbed by the capillary column. The extent or amount of the extraction is found to depend on parameters such as: the phase ratio of the stationary phase coated on the inner wall of the capillary; the extraction temperature; the linear velocity of the aqueous solution through the capillary; the total volume of the sorbing phase; and the original concentration of organic in water before extraction. Stationary phase type will also play a role in the extraction. Variation of the experimental factors, using BTEX extraction as a model system, allowed the derivation of an empirical equation to describe the extraction performance. With this equation it is possible to predict the minimum volume required to be passed through different types of capillary for different solutes to ensure equilibrium extraction. This volume corresponds to the onset of 100% breakthrough. Phenols were used to validate the approach using a polar capillary stationary phase. Experimental data agreed with predictions.