Automated determination of weakly acidic and basic pollutants in surface water by on-line electrodialysis sample treatment and column liquid chromatography

Abstract

The use of on-line electrodialysis for the treatment of natural waters prior to the column liquid chromatographic determination of polar pollutants is described. The influence of several system parameters, such as electrical potential, donor flow rate, sample volume and pore size of the separation membrane, on the enrichment of various weak acids and bases and on the removal of interfering matrix components was evaluated. Further, the effect of a pH shift taking place in the sample during electrodialysis was studied. The completely automated procedure allows a 7–10-fold selective enrichment of the analytes (several anilines and chlorinated phenoxy acids) from 750 µl surface water samples within 25 min by applying a donor flow rate of 50 µl min^–1 and a potential of 7.5–10 V. A separation membrane with 3.5 kDa pore size removes more of the matrix and yields 2–5-fold lower detection limits than a 15 kDa membrane. Under these conditions and using LC with UV detection, detection limits for all compounds studied were in the range 0.5–5.0 µg l^–1 in surface water.