Sensitive electrochemical detection of methyl parathion in the presence of para-nitrophenol on a glassy carbon electrode modified by a functionalized NiAl-layered double hydroxide

An inorganic–organic composite material was prepared by the insertion of bis(ethylhexyl)hydrogen phosphate (BEHP) within the interlayer space of a nickel-aluminum–layered double hydroxide (NiAl LDH). X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared were used to characterize the pristine and modified LDH (NiAl–BEHP), which together confirm the intercalation of BEHP in the mineral structure. Cyclic voltammetry using Fe(CN)₆]^3? as an anionic redox probe demonstrated a significant decrease in the anion exchange capacity of NiAl upon modification. Used as electrode modifier for methyl parathion (MP) detection, a remarkable increase in MP signal on NiAlBEHP–modified glassy carbon electrode (GCE/NiAl–BEHP) was observed, because of the high hydrophobicity character of the modified LDH. The signal assigned to the electroactivity of the nitro group being less stable than that of the reduction of the nitroso group, the use of both functions was explored for the calibration experiments. Sensitivities of 0.79 μA μM^?1 and 0.14 μA μM^?1 were obtained, with detection limits of 2.28 × 10^?8 and 12.4 × 10^?8 mol L^?1 for nitro and nitroso groups, respectively. However, the linearity range was more important for the nitroso group (0.5–12 μM) as compared to the nitro group (0.5–3.5 μM). Moreover, the signal of the nitroso group showed poor interference with some chemical species likely to be encountered in the presence of MP. The GCE/NiAl-BEHP–modified electrode was particularly effective for the differentiation of 4-nitrophenol (4-NP) from MP. Interestingly, the decrease in the sensor sensitivity was negligible (0.13 μA μM^?1) when the calibration curve of MP was plotted in the presence of 1 μM of 4-NP. The poor efficiency of the sensor to quantify 4-NP was probably because of the high organophilic character of the electrode material. The developed method was successfully applied to quantify MP in spring water.