SENSITIVE DETERMINATION OF PARAQUAT AND DIQUAT AT THE SUB-NG ML(-1) LEVEL BY CONTINUOUS AMPEROMETRIC FLOW METHODS

Two methodologies are described for the determination of paraquat and diquat. The first is based on the pre-treatment of an electrode with a surfactant solution, which improves the electrochemical determination of the herbicides. Linear calibration graphs were obtained in the ran ges 10-80 and 10-100 ng ml(-1) for paraquat and diquat, respectively. The limits of detection were 6.32 for paraquat and 4.80 ng ml(-1) for diquat. The method was applied to the determination of the herbicides in synthetic water samples. The second methodology is based on the pre concentration of paraquat and diquat in a minicolumn packed with a cat ion-exchange material. The determination ranges and detection limits d epend on the sample volume used (5-50 ml). Thus, 50 ml of sample provi des limits of detection of 0.016 and 0.020 ng ml(-1) for paraquat and diquat, respectively. The applicability of the method was demonstrated with the determination of the herbicides in both synthetic and real w ater samples.