Sensitive voltammetric responses and mechanistic insights into the determination of residue levels of endosulfan in fresh foodstuffs and raw natural waters

This paper describes the electroanalytical study of the organochlorine pesticide endosulfan (EDS) using square-wave voltammetry. The electrochemical behaviour showed a quasi-reversible process on a hanging mercury drop electrode (HMDE) in acid medium attributed to reduction of the carbon-chlorine bond. The constant of change transfer obtained for this process was 354 s(-1). The redox mechanism was confirmed by quantum-chemical (Density Functional Theory, DFT) studies. The optimised experimental and voltammetric parameters were 0.04 mol L-1 Britton-Robinson buffer (pH 4.0), the pulse potential frequency of 200 s(-1), the amplitude of the pulse of 20 mV, and the height of the potential step of 4 my. Analytical parameters such as linearity range, equation of the analytical curves, correlation coefficients, detection and quantification limits, recovery values, precision, and accuracy were obtained. The procedure was applied to the analysis of pesticide in complex samples: sugar cane, tomato, and raw natural waters. The recovery values demonstrated that the proposed methodology is suitable for determining EDS in such samples. The results indicated that the proposed procedure is stable and sensitive, with good reproducibility, and no complex procedure was necessary for sample preparation. The development of this electroanalytical procedure is therefore appropriate, as it provides adequate sensitivity and reliable methodology. (C) 2013 Elsevier B.V. All rights reserved.