title: Multiple square wave voltammetry for analytical determination of paraquat in natural water, food, and beverages using microelectrodes.
abstract: This paper reports on the use of multiple square wave voltammetry (MSWV) for analytical determination of paraquat herbicide at gold microelectrode (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 0.0V at -1.2V versus Ag/AgCl 3.0 mol L(-1). The paraquat herbicide presented two reduction peaks, in -0.69V and -0.99V, 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 microgL(-1) (0.044 ppb) and 0.146 microg 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.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, CP 780, São Carlos, SP, Brazil. djenaine@iqsc.usp.br
authors.forename: Djenaine De
authors.initials: DD
authors.lastname: Souza
authors.forename: Sergio A S
authors.initials: SA
authors.lastname: Machado
authors.forename: Roberto C
authors.initials: RC
authors.lastname: Pires