AUTOMATED-DETERMINATION OF WEAKLY ACIDIC AND BASIC POLLUTANTS IN SURFACE-WATER BY ONLINE ELECTRODIALYSIS SAMPLE TREATMENT AND COLUMN LIQUID-CHROMATOGRAPHY

The use of on-line electrodialysis for the treatment of natural waters prior to the column liquid chromatographic determination of polar pol lutants 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 a nd bases and on the removal of interfering matrix components was evalu ated. Further, the effect of a pH shift taking place in the sample dur ing electrodialysis was studied. The completely automated procedure al lows a 7-10-fold selective enrichment of the analytes (several aniline s and chlorinated phenoxy acids) from 750 mu l surface water samples w ithin 25 min by applying a donor flow rate of 50 mu l min(-1) and a po tential of 7.5-10 V. A separation membrane with 3.5 kDa pore;size remo ves 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 detect ion, detection limits for all compounds studied were in the range 0.5- 5.0 mu g l(-1) in surface water.