Development and Validation of Spectrophotometric and Spectrofluorimetric Methods for Glufosinate-Ammonium Herbicide and Carbofuran Insecticide Contamination in Environmental Samples

The excessive use of glufosinate˗ammonium herbicide and carbofuran insecticide in agriculture leaves residues on agricultural samples and contaminates groundwater and surface water bodies through surface runoff and through leaching. To monitor pollution from the use of these pesticides, two simple, accurate and precise optical methods for their determination have been developed and validated in the commercial formulation and agricultural samples, viz., water, grains and vegetables. The first method is based on the reaction of the amino function of both pesticides with carbon disulfide and Ni(II) acetate in an aqueous acetonitrile medium and the measurement of color developed at 380 and 365 nm for glufosinate˗ammonium and carbofuran, respectively. Beer’s law was valid within a concentration range of 0.4–8 and 0.4–9 µg/mL for glufosinate˗ammonium and carbofuran, respectively. The second spectrofluorimetric method is based on the condensation of the primary amino group of glufosinate˗ammonium and carbofuran with acetylacetone and formaldehyde (Hantzsch reaction) in the presence of buffer of pH 5.5 producing a yellow˗colored product. The fluorescence intensity of the reaction products was measured at an emission wavelength of 470 nm after excitation at a wavelength of 380 nm for glufosinate-ammonium and 388 nm for carbofuran. The linearity range found was 0.13–5 and 0.14–6 µg/ mL for glufosinate˗ammonium and carbofuran respectively. All the variables affecting the reactions, such as hydrolysis time, heating time, pH, concentration and volume of reagent were carefully studied and optimized. The high recoveries of glufosinate-ammonium and carbofuran from spiked water, grain and vegetable samples in both methods indicate good accuracy and precision of the methods.