SENSITIVE SPECTROPHOTOMETRIC METHODS FOR DETERMINATION OF SOME ORGANOPHOSPHORUS PESTICIDES IN VEGETABLE SAMPLES

Three rapid, simple, reproducible and sensitive spectrophotomettic methods (A, B and C) are described for the determination of two organophosphorus pesticides, (malathion and dimethoate) in formulations and vegetable samples. The methods A and B involve the addition of an excess of Ce4+ into sulphuric acid medium and the determination of the unreacted oxidant by decreasing the red color of chromotrope 2R (C2R) at a suitable lambda(max) = 528 nm for method A, or a decrease in the orange pink color of rhodamine 6G (Rh6G) at a suitable lambda(max) = = 525 nm. The method C is based on the oxidation of malathion or dimethoate with the slight excess of N-bromosuccinimide (NBS) and the determination of unreacted oxidant by reacting it with amaranth dye (AM) in hydrochloric acid medium at a suitable lambda(max) = 520 nm. A regression analysis of Beer-Lambed plots showed a good correlation in the concentration range of 0.1-4.2 mu g mL(-1) The apparent molar absorptivity, Sandell sensitivity, the detection and quantification limits were calculated. For more accurate analysis, Ringbom optimum concentration ranges are 0.25-4.0 mu g mL(-1). The developed methods were successfully applied to the determination of malathion, and dimethoate in their formulations and environmental vegetable samples.