Electroanalytical studies of glyphosate and aminomethylphosphonic acid in aqueous medium using copper and hanging mercury drop electrodes

Abstract

Glyphosate (GLYP) is commonly used in agriculture to control weeds. GLYP residue and its main metabolite, aminomethylphosphonic acid (AMPA), can be found in crops, vegetables, fruits, soil and also ground water which raised concern over the problems regarding to the environmental contaminations. These compounds can be detected and determined by gas chromatography (GC), high performance liquid chromatography (HPLC), ion chromatography (IC), capillary electrophoresis (CE) or enzyme linked immunosorbent assay (ELISA). However, most of these methods are time consuming, involve the use of toxic solvents, require complicated pre-preparation and high cost of instrumentation. Therefore, in the present study voltammetric method based on the use of copper electrode (CuE) and hanging mercury drop electrode (HMDE) were used to investigate the electrochemical behaviour and quantitative analysis of GLYP and AMPA. Investigations were carried out by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse cathodic stripping voltammetry (DPCSV) techniques based on the reduction (cathodic current) and oxidation (anodic current) of Cu(II) in phosphate buffer at pH 6.4. Based on anodic and cathodic currents of the CuE working electrode using DPV and DPCSV techniques, linear calibration curves were obtained in the range of 1.18 up to 5.92 × 10-6 M and 7.20 up to 36.02 × 10-6 M for GLYP and AMPA respectively. The limits of detection (LOD) based on anodic current for GLYP at -80 mV vs saturated calomel reference electrode (SCE) and AMPA at -96 mV vs SCE by DPV technique were 3.24 × 10-7 M and 2.68 × 10-6 M respectively. The LOD based on cathodic current for GLYP at -180 mV vs silver/silver chloride reference electrode (Ag/AgCl) and AMPA at -190 mV vs Ag/AgCl were 4.69 × 10-7 M and 2.67 × 10-6 M respectively. The LOD by DPCSV with CuE working electrode were 3.11 × 10-7 M and 2.09 × 10-6 M for GLYP at -180 mV vs Ag/AgCl and AMPA at -190 mV vs Ag/AgCl respectively. Determination of GLYP and AMPA by HMDE requires addition of Cu(II) into the test solution. Linear calibration curves by HMDE were obtained in the range of 2.96 up to 14.79 × 10-7 M and 1.35 up to 6.75 × 10-6 M for both DPV and DPCSV. The LOD of GLYP at 0 mV vs Ag/AgCl and AMPA at -3 mV vs Ag/AgCl by HMDE were 7.41 × 10-8 M and 6.05 × 10-7 M respectively using DPV. The LOD by DPCSV technique for GLYP at -3 mV vs Ag/AgCl and AMPA at 0 mV vs Ag/AgCl by HMDE were 5.40 × 10-8 M and 2.64 × 10-7 M respectively. The DPCSV technique with CuE and HMDE working electrodes for the determination of GLYP and AMPA have good recoveries (94 - 98%) based on application to real samples.