Estudo eletroanalítico do herbicida paraquat em soluções aquosas por voltametria de onda quadrada utilizando ultramicroeletrodos

Abstract

Recebido em 18/7/02; aceito em 21/2/03 ELECTROANALYTICAL STUDY OF THE PARAQUAT HERBICIDE IN AQUEOUS SOLUTION BY SQUARE WAVE VOLTAMMETRY USING ULTRAMICROELECTRODES. The electrochemical behavior of paraquat on Pt, Au and carbon fiber ultramicroelectrodes were studied in laboratory samples by square wave voltammetry at high frequencies. The results showed two reversible peaks for paraquat reduction, in agreement to the literature data. The first peak was associated to the reduction of paraquat molecule in solution, with the further adsorption of the intermediate on the electrode surface. This adsorbed species undergoes to electroreduction in a reaction associated to the second voltammetric peak. The variation in pH and square wave parameters showed the best conditions to reduce paraquat as pH 5.0, frequency as high as 1000 s-1 , scan increment of 2 mV and square wave amplitude of 50 mV. At such conditions, a variation of paraquat concentrations from 4.3 x 10-6 to 1.66 x 10-4 mol L-1 presented values for the detection limit equal to 3.9, 6.2 and 20.3 ppb on Pt, Au and carbon, respectively, at 1000 s-1. These values are quite below 17 the allowed limit of paraquat in drinking water.