AUTOMATED ION-PAIR EXTRACTION AND ION-PAIR CHROMATOGRAPHY - A VERSATILE METHOD IN WATER ANALYSIS FOR THE DETERMINATION OF HIGHLY POLAR MICROPOLLUTANTS

An automated HPLC method is presented which combines on-line ion-pair extraction on small exchangeable RP-C18 precolumns (RP-IPE) with ion-p air chromatography (RP-IPC). Weakly acidic herbicides - carboxylic aci ds, phenols, and the N-H acidic bentazone - and strong acids, e.g. aro matic sulfonic acids, can be determined simultaneously. Performance da ta are given. The tetrabutylammonium ion pairs of all investigated com pounds are readily transferred from the RP-C18 precolumn to the analyt ical column by a phosphate buffer/methanol gradient. This is also true for the chlorinated phenoxy acids which, in earlier off-line extracti on experiments, could not be desorbed from the RP-C18 material by the lower polar acetone. The RP-IPC is carried out at neutral pH where wea kly acidic compounds appear in their stronger UV absorbing dissociated form. Compared to conventional reversed phase chromatography using an acidified eluent, the sensitivity of UV detection is markedly enhance d, especially for the phenol herbicides and bentazone. In addition, ph enols can be detected more selectively because they show a second inte nse absorption band in the wavelength range between 280 nm and 290 nm, where there are only little interferences with the matrix. Due to min iaturization and automation, the online combination IPE/IPC allows a l arge sample throughput at a lower consumption of solid phase material and organic solvents. Time consuming manual steps are totally missing. The IPE/IPC technique is well suited as a screening method for fate s tudies of polar micropollutants, e.g. for monitoring the efficiency of different water treatment technologies. An example for balancing an a ctivated carbon filter is presented.