MEASUREMENT OF PHENOLS ON A LOOP-SUPPORTED LIQUID-FILM BY MICELLAR ELECTROKINETIC CHROMATOGRAPHY AND DIRECT UV DETECTION

This paper describes a direct measurement of phenolic substances in th e gas phase at levels relevant to occupational health by micellar elec trokinetic chromatography (MEKC) using direct ultraviolet detection. A small circular loop (2 mm O.D.) is formed with 100 mm Pt-wire at the sampling end of a fused-silica capillary. The capillary tip of the sam pling end is present at the center of the loop and in the same plane. A thin film of 0.50 mM NaOH is formed on the loop by immersion and wit hdrawal. The film is in fluid communication with the capillary and act s as an absorber for gaseous phenols. Gas sampling is performed by tra nsferring the film-bearing loop into a chamber through which air is as pirated for a preset time at a preselected flow-rate (typically 1 min at 100 cm(3)/min). A part of the film content is then introduced into the capillary by gravity injection and then MEKC is performed. A total of twelve chloro- and nitrophenols were selected for this study. Unde r the above sampling conditions, limits of detection (LODs) for variou s phenols range from high-single-digit to low-double-digit ppbv levels . The effect of several critical parameters, such as the composition o f the liquid film and the MEKC running electrolyte, sampling period an d film evaporation on the collection efficiency, separation efficiency and calibration behaviour are described.