The electrochemical degradation of methyl parathion (MP) has been investigated by using carbon fiber microelectrodes (CFME) as working electrode and acetate buffer pH 5.2 as supporting electrolyte. pnitrophenol (PNP) and p-aminophenol (PAP) recognized as by-products of MP degradation process have been detected and identified in real time using square wave voltammetry. This study shows for the first time that CFME could be used to follow MP degradation in real time and to identify its stables metabolites.

Abstract3-methyl-4-nitrophenol (MNP) is the main by-product of the organophosphate insecticide fenitrothion (FT), used in locust control. MNP is highly toxic because it is an endocrine disruptor and then may cause adverse in the biological systems. Then, it is necessary to develop analytical methods for determination of this pollutant in the environment. In this sense, we reported herein the development of an electrochemical sensor for the detection of 3-methyl-4-nitrophenol (MNP), one of the metabolites of fenitrothion (FT), by using naked and modified carbon fiber microelectrode (CFME) by nickel tetrasulfonated phthalocyanine polymer (CFME/p-NiTSPc). The voltammogram showed that MNP presents one irreversible anodic peak corresponding to the oxidation of the phenol group at 0.9 V vs Ag/AgCl. The effect of pH of the buffer on the peak current and SWV parameters such as frequency, scan increment and pulse amplitude were investigated in order to optimize the electrochemical response of the sensor. The obtained results lead to the following optimum value: pH = 6; frequency = 25 Hz, pulse amplitude = 50 mV, scan increment = 10 mV. With these optimum values, the calibration curves show that the peak current varied linearly upon MNP concentration leading to a limit of detection (LoD) for naked CFME close to 3 µg/L whereas for CFME modified by p-NiTSPc, it reaches 0.75 µg/L. This results prove that the presence of p-NiTSPc increasing the sensitivity of the sensor could be used to monitor 3-methyl-4-nitro-phenol residue in real matrix.

This paper presents an evaluation using carbon fiber microelectrode (CFME) for the determination of glyphosate in soils from Burkina Faso treated with Glyphonet SL 360 by square wave voltammetry (SWV). The maximum intensity of the electrochemical response signal of glyphosate has been optimized and conditions using a 0.2 M of phosphate buffer solution at pH 5.2 as supporting electrolyte and the SWV parameters frequency of 60 Hz, a scan increment of 10 mV and a pulse height of 60 mV. The limit of detection for glyphosate in the Glyphonet SL 360 formulation was 25 µg L -1 while the quantification limit was 83 µgL -1 with a linear dynamic range up to 50 µg L -1 . In these conditions, a sequence of experiments led to recoveries in the range 88.5 to 102.3% for soil samples spiked with 50, 100 and 200 µgL -1 of glyphosate with a standard deviation of 11.5, 4.2 and 2.3% respectively indicating the precision of the method. The optimized method was successfully applied to determine the residues of glyphosate in soils collected in the fields in two different dates from the application period.