Spectrophotometric method for determination of paraquat in food and biological samples.

A sensitive spectrophotometric method was developed for determination of paraquat, a widely used herbicide. Paraquat was reduced with glucose in an alkaline medium, and the blue radical ion obtained was measured at 600 nm. Beer's law was obeyed at 0.1-1.2 ppm paraquat. The molar absorptivity was 1.26 x 10(5) L mol-1 cm-1. The standard deviation and relative standard deviation were +/- 0.007 and 2.0%, respectively, for 5 micrograms paraquat/10 mL analyzed over 7 days. The method was free from interference by other commonly used pesticides and metal ions. The method may be used to the determine paraquat in plants, fruits, grains, water, blood, and urine.