Flow injection spectrofluorimetric determination of malathion in environmental samples using on-line photooxidation

A simple, rapid, sensitive and precise method for the determination of malathion in a flow-injection system is described. The method is based on the decomposition of malathion in the presence of alkaline peroxydisulphate upon irradiation with UV light. The phosphate produced in the photochemical process is made to react with molybdate in dilute nitric acid to form phosphomolybdic acid, which oxidises thiamine to thiochrome. The thiochrome can then be fluorimetrically monitored at 440 nm with excitation at 375 nm. The new approach allows the determination of malathion in a wide concentration range (20-2000 ng mL(-1)) with a throughput of 70 samples per hour. The applicability of the method was demonstrated by determining malathion residues in agricultural waste water, grains and vegetables.