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

摘要

This paper describes a direct measurement of phenolic substances in the gas phase at levels relevant to occupational health by micellar electrokinetic 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 sampling 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 withdrawal. The film is in fluid communication with the capillary and acts as an absorber for gaseous phenols. Gas sampling is performed by transferring the film-bearing loop into a chamber through which air is aspirated 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. Under the above sampling conditions, limits of detection (LODs) for various phenols range from high-single-digit to low-double-digit ppbv levels. The effect of several critical parameters, such as the composition of the liquid film and the MEKC running electrolyte, sampling period and film evaporation on the collection efficiency, separation efficiency and calibration behaviour are described.