Electrochemically pretreated zeolite-modified carbon-paste electrodes for determination of linuron in an agricultural formulation and water

Abstract

A simple and inexpensive, yet highly sensitive electrochemical method for quantifying linuron in tap and distilled water and in agricultural formulations was developed using electrochemically pretreated zeolite-modified carbon-paste electrodes (ZMCPEs). Compared with untreated ZMCPEs, the electrochemically pretreated electrodes showed significantly enhanced peak currents for linuron oxidation. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were used to examine the structure of the zeolite-modified and unmodified carbon-paste electrodes (CPEs). ZMCPEs were electrochemically characterized using cyclic voltammetry, chronocoulometry, square-wave voltammetry, and electrochemical impedance spectroscopy. A mechanism for linuron oxidation on ZMCPE surfaces was proposed. The electrochemical variables taken into account were electrode area, number of transferred electrons, electron transfer coefficient, electrode reaction standard rate constant, surface coverage, and capacitance of the electric double layer. Zeolite was found to have a strong influence on these variables. The electrochemical procedure applied to linuron was developed using electrochemically pretreated ZMCPEs under optimal conditions. Linuron oxidation currents exhibited linear concentration in the 87.36 to 625.72 nmol L−1 range, with a limit of detection of 22.57 nmol L−1. The proposed electrochemical method was employed to quantify linuron in tap and distilled water and in a commercial agricultural formulation. Recovery rates were in the 99% to 101% range, indicating that the method can be applied to quantify linuron in these matrices. The recovery rates attained by applying the methodology developed showed high concordance with results obtained using HPLC, having a relative standard deviation of less than 1.5%.