On-line liquid chromatographic trace enrichment and highperformance liquid chromatographic determination of diquat, paraquat and difenzoquat in water

For the trace-level determination of diquat, paraquat and difenzoquat in drinking and surface water, a fully automated method using on-line trace enrichment, LC separation and UV detection is described. An automatic sample preparation device (OSP-2, Merck) was employed as the sample preparation unit. The three herbicides were trapped from the flowing water sample by adsorption on a silica cartridge placed in a circular cartridge magazine, then the load cartridge was moved to the elution side. On the elution side, the herbicides were transferred to the analytical column by the mobile phase. Detection limits for the three herbicides below 20 ng/l were obtained after preconcentrating 200 ml of drinking water. The total analytical procedure was applied for the monitoring of the three herbicides in drinking and surface water.