Cloud-point extraction associated with voltammetry: preconcentration and elimination of the sample matrix for trace determination of methyl parathion in honey

Abstract

This work presents the association of cloud point extraction (CPE) and electroanalysis for the selective and sensitive determination of methyl parathion (MP) in honey. The CPE step provided the pre-concentration of MP from a complex sample, in which the optimized extraction parameters (Triton X-100 concentration of 0.75% w/v, NaCl concentration of 1.0% w/v and heating time of 30 min) were investigated using a factorial design (2³). The detection of MP was performed using a cathodically pre-treated boron-doped diamond (BDD) working electrode and square wave voltammetry (SWV), after a suitable dilution of the CPE extract in Britton–Robinson buffer pH 6.0 as the supporting electrolyte. MP presented three electrochemical processes over the BDD surface, but only the reduction peak at around −0.7 V was monitored for the MP determination (higher detectability). Improved reproducibility was reached by applying an in situ cleaning step (+2.0 V for 15 s) followed by a re-activation process (−2.0 V for 15 s) between measurements. Using the optimized variables, a linear range between 0.1 and 2.0 μmol L⁻¹ was obtained for MP with a limit of detection of 0.006 μmol L⁻¹, a 6-fold lower value when compared with the value attained without the CPE step. The experimental enrichment factor of MP was 6.1. Also, the optimized CPE allowed the determination of MP in honey samples with good accuracy (recovery between 94 and 106%), which was not possible using direct detection (without CPE) due to the matrix interference. This is the first paper that demonstrates the combination of CPE and electroanalysis for the determination of an organic compound.