A new spectrophotometric method for the determination of glyphosate: statistical optimization and application in biodegradation studies

Abstract

Glyphosate (N-phosphonomethylglycine) is extensively used as herbicide against annual and perennial weeds. In the present study, we report a new colorimetric method for the estimation of glyphosate which is based on formation of copper dithiocarbamic acid complex from glyphosate. Glyphosate formed yellow colored complex (λmax = 372 nm) when it was reacted with carbon disulfide (CS2) and copper(II)nitrate in alkaline medium. Using Box–Behnken design (BBD), glyphosate, CS2, copper(II) nitrate, and reaction time were found to influence the absorbance at 372 nm significantly (p < 0.05). The quadratic model developed for the absorbance at 372 nm fitted well to the data (p < 0.0001, F = 21.62, R2= 0.96, adjusted R2= 0.92, predicted R2= 0.75). The optimum concentration of glyphosate, CS2, copper (II) nitrate, and reaction time for maximum absorbance were found to be 500 µg/mL, 1.0% (v/v), 150 µg/mL, and 60 min, respectively. The predicted value of absorbance at 372 nm (0.450) agreed fairly well with the actual value of 0.480. The proposed method obeyed Beer’s law up to 500 µg/mL and showed limit of detection (LOD) and limit of quantitation (LOQ) of 28.9 and 96.4 µg/mL, respectively, with R2of 0.9947. Glycine, aminomethylphosphonic acid (AMPA), cultivation medium components, and soil extract did not interfere in the color complex formation. Using the method, under shake flask conditions, a bacterial isolate Stenotrophomonas maltophilia GP-1 exhibited biodegradation efficiency of 84% after 100 h suggesting that the above method is suitable for study of biodegradation of glyphosate.