An L-cysteic acid-modified screen-printed carbon electrode for methyl parathion determination

This work demonstrates the development and validation of a non-enzymatic sensor consisting of an L-cysteic acid-modified screen-printed carbon electrode (LCA-SPCE) sensor for the determination of the hazardous organophosphorus pesticide methyl parathion (MP) using square-wave adsorptive stripping voltammetry (SWAdSV). The surface of LCA-SPCE was investigated using time of flight secondary ion mass spectrometry to confirm successful preparation of the LCA surface layer. In order to obtain the highest electrochemical response, the accumulation time and pH of the 0.1 M phosphate buffer solution (PBS) supporting electrolyte were opti-mized. Then, SWAdSV method validation was performed in 0.1 M PBS at pH 6.00, an accumulation potential at the open circuit potential, and an accumulation time of 120 s. Since an intensive background was observed from the measurement of blank solution on the LCA-SPCE, a background subtraction procedure was employed. Partial method validation of the LCA-SPCE sensor was performed by determining the limit of detection (LOD), the limit of quantification (LOQ), the linear concentration range, accuracy, and precision. The developed method has a very low LOD and LOQ of 2.5 mu g/L and 5.0 mu g/L, respectively, and a linear concentration range of 5.0-84.3 mu g/L (R2 = 0.9948). The average recovery and relative standard deviation were 109.6 % and 7.1 %, respectively (n = 6). This work also demonstrates the advantageous use of the multiple standard addition methodology compared to the calibration curve for analysing MP by means of an LCA-SPCE. Furthermore, electrochemical impedance spectroscopy was performed to show the differences between the bare-SPCE and LCA-SPCE. Finally, the appli-cation of the developed and validated LCA-SPCE sensor for the determination of MP was successfully employed for a real water sample (tap water), which showed the high accuracy and precision of the method. In addition, the interference and matrix effects were also studied.