Spectrophotometric determination of endosulfan using thionin and methylene blue as chromogenic reagents.

A simple, selective and sensitive spectrophotometric method is proposed for the determination of widely used organochlorine pesticide endosulfan using thionin and methylene blue as chromogenic reagents. The method is based on the liberation of sulfur dioxide from endosulfan by adding acid reagent and alcoholic potassium hydroxide. The liberated sulfur dioxide is passed through potassium iodate solution and the iodine so liberated bleaches the violet color of thionin and blue color of methylene blue and is measured at 600 nm and 665 nm respectively. This decrease in absorbance is directly proportional to the endosulfan concentration. The Beer's law is obeyed in the range of 0.4-7.0 and 0.2-9.0 microg mL(-1) of endosulfan using thionin and methylene blue as reagents respectively. The molar absorptivity and Sandell's sensitivity were found to be 1.05 x 10(5) and 5.03 x 10(4) L mol(-1) cm(-1), 3.85 x 10(-3) and 8.10 x 10(-3) microg cm(-2) of endosulfan using thionin and methylene blue as reagents respectively. The method has been applied for the determination of endosulfan in water, soil and vegetables.