Quantitative Evaluation of Generic Glyphosate Using Carbon Paste Electrode Electrochemically Modified with Copper Ions

— Generic products are not identical to their branded equivalents. They are typically off-patent. Therefore, this paper suggests a selective, reliable, and accurate electrochemical method for quantifying the original and generic glyphosate from Monsanto Roundup ® —USA and Rotam Agrochemicals—Hong Kong. The reliability of the suggested electroanalytical method was assured. An electrochemically modified carbon paste electrode was used as a working electrode. This working electrode was constructed by depositing a copper layer electrochemically using chronoamperometry under continuous stirring. The copper deposition was conducted for 180 s at the potential of –0.8 V from an aqueous solution of copper sulphate pentahydrate at pH 6.5. Adjust by adding phosphate buffer. Cyclic voltammograms for electrochemically modified CPE versus Ag/AgCl were recorded between (–0.8…–1.4 V) at a scan rate of 0.1 V s –1 in solutions with and without glyphosate. The results showed an enhancing in the oxidation peak current of the copper previously deposited on CPE by the addition of glyphosate. This enhancing in copper oxidation peak may be attributed to glyphosate adsorption on the surface of the electrode and formation of a complex. SW-ASV method was used as an efficient electroanalytical technique for glyphosate quantification. The operating parameters such as accumulation potential and accumulation time were optimized to give maximum oxidation peak current of copper. Calibration curves were constructed in a concentration range (2 × 10 –6 –2 × 10 –4 mol L –1 ) for generic, original and standard glyphosate. Calibration curve method was adopted in a comparison. It was observed that there are very minor differences in the slopes of generic, original, and standard glyphosate (0.2982–0.2993–0.2957 μA/μM) respectively.