On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high-performance liquid chromatography with diode-array detection

The need for a rapid, sensitive and reliable analytical method for cyanobac terial toxins, microcystins, has been emphasized by the awareness of toxic cyanobacteria as a human-health risk through drinking water. A new high-per formance liquid chromatographic method with column switching was developed for the determination of microcystin-LR, -RR and -YR from water samples wit hout pre-purification. The filtered water sample was passed through a Zorba x CN precolumn at a flow-rate of 3 ml/min for on-line trace enrichment. Aft er valve switching, concentrated analytes were eluted in back-flush mode an d separated on a Luna C-18 column with a gradient of acetonitrile -20 mM ph osphate buffer (pH 2.5). The method showed excellent precision, accuracy an d speed with detection limits of 0.02 mu g/ml from 100 ml of surface water. The total analysis time per sample was about 90 min. This method improves reliability, sensitivity and sample throughput, and shortens the analysis t ime compared to analysis methods using off-line solid-phase extraction. (C) 1999 Elsevier Science B.V. All rights reserved.