AUTOMATED-DETERMINATION OF PYRETHROID INSECTICIDES IN SURFACE-WATER BY COLUMN LIQUID-CHROMATOGRAPHY WITH DIODE-ARRAY UV DETECTION, USING ONLINE MICELLE-MEDIATED SAMPLE PREPARATION

A liquid chromatographic method using gradient elution and diode array UV detection for the trace level determination of seven synthetic pyrethroids is described. The procedure involves automated on-line preconcentration on precolumns containing octadecyl-bonded silica using a Prospekt. Although the analytes display a ''mixed'' hydrophobic/hydrophilic behaviour, both breakthrough on the precolumn and adsorption to inner walls and surfaces can be prevented by adding Brij-35, a neutral surfactant, to the aqueous sample. The procedure has been tested for the analysis of surface water; detection limits typically are at the sub-mu g/l level and repeatability is excellent. The automated system is robust and there are no maintenance problems.