Multiple square wave voltammetry for analytical determination of paraquat in natural water, food, and beverages using microelectrodes

This paper reports on the use of multiple square wave voltammetry (MSWV) for analytical determination of paraquat herbicide at gold micro-electrode (Au-ME) in different samples of natural water, food, and beverages. In this work, the MSWV consisted in a sequence of four pairs of potential pulse in the same step and the interval potential evaluated was of the 0.0 V at -1.2 V versus Ag/AgCl 3.0 mol L-1. The paraquat herbicide presented two reduction peaks, in -0.69 V and -0.99 V, with profile of the redox process totally reversible, and the use of multiple pulses allowed a detection of nanomolar levels after the optimization of experimental and voltammetric conditions. Analytical curves were constructed for pulse potential frequency of 250 s(-1), pulse amplitude of 50 mV, scan increment of 2 mV and pulse number of 8 pulses in a same step. The two reduction peaks showed that the peak currents were found to be directly proportional to the pesticide concentration in the range comprised between 5.0 x 10(-7) mol L-1 and 1.04 x 10(-5) mol L-1. With this, it was possible to determine detection limits (DL), which resulted in 0.044 mu g L-1 (0.044 ppb) and 0.146 mu g L-1 (0.146 ppb), respectively, for peak 1 and peak 2. DL results, obtained using MSWV, were 2-3 orders of magnitude lower (10(-2) to 10(-3)) less than those observed for traditional square wave voltammetry or published in literature, clearly pointing to the advantages arising from the possibility of using a MSWV for analytical purposes in contaminated matrices. In addition, the proposed methodology was applied in different samples of natural water, food and beverages without pre-treatment or pre-concentration step, where a recovery measurement indicated that the methodology could be employed to analyze paraquat in such matrices. (c) 2006 Elsevier B.V. All rights reserved.