Assessment of fenobucarb and propoxur insecticides in environmental samples by spectrophotometric and spectrofluorimetric methods

Abstract

The widespread use of fenobucarb and propoxur insecticides for agricultural and non-agricultural purposes causes undesirable effects on human health and environment due to their residues in surface and ground water resources. In view of this, two new, simple, accurate, sensitive, economical and reproducible optical methods have been investigated for the determination of fenobucarb and propoxur insecticides in pure form, in their commercial formulations, and agricultural samples viz. water, grains and vegetables. The methods are based on the alkaline hydrolysis of the insecticides to methyl amine and the reaction of the latter to give colored products. In the spectrophotometric method, the methyl amine formed, in presence of carbon disulfide (CS₂) and Ni(II) acetate gives a yellow colored complex, which was measured at 370 nm. Beer’s law is valid in the concentration range of 0.41–8.29 and 0.42–8.37 µg mL⁻¹ for fenobucarb and propoxur, respectively. The spectrofluorimetric method is based on the study of yellow-colored product, formed by the condensation of methyl amine with acetylacetone and formaldehyde (Hantzsch reaction), at pH 5.5. The reaction product exhibits fluorescence intensity at an emission wavelength of 470 nm after excitation at a wavelength of 390 nm for both fenobucarb and propoxur insecticides. The method has linearity range of 0.14–5.53 and 0.14–5.58 µg mL⁻¹ for fenobucarb and propoxur, respectively. The different factors which affect the reactions were thoroughly studied and optimized. The proposed methods have been successfully applied to assay both insecticides in their commercial formulations and for recovery study from spiked environmental samples. The good results of recoveries of both insecticides demonstrate the accuracy and precision of both methods.

Graphical abstract