Electrochemical behavior of metribuzin on a glassy carbon electrode in an aqueous medium including quantitative studies by anodic stripping voltammetry

Abstract

O comportamento eletroquímico do herbicida metribuzin foi estudado em solução aquosa com eletrodos de carbono vítreo, em pasta de carvão/nujol, carvão/óleo de mamona e pela utilização de voltametria cíclica, voltametria de onda quadrada, voltametria de pulso diferencial, coulometria e eletrólises em potencial controlado, para fins de quantificação e estudos de degradação. Os produtos majoritários obtidos a partir da eletrólise redutiva de metribuzin, após o consumo de 8,26 mol elétron mol-1 , foram o desaminometribuzin e o dicetometribuzin. A onda anódica observada após a eletrorredução está relacionada à oxidação do tiolato de metila, gerado no processo eletrolítico. Essa onda foi utilizada para a determinação quantitativa de metribuzin em amostra comercial, por meio de voltametria de redissolução anódica. De maneira a promover descontaminação, por eliminação do herbicida, o processo eletro-Fenton foi utilizado e levou a 80% de mineralização de metribuzin. The electrochemical behavior of the herbicide metribuzin was studied in an aqueous solution on glassy carbon, carbon paste/Nujol oil and carbon paste/castor oil using cyclic voltammetry, square-wave voltammetry, differential pulse voltammetry, controlled-potential coulometry and electrolysis, for quantification and decontamination purposes. The main electrolytic products obtained from the reduction of metribuzin, after consumption of 8.26 mol electron mol-1 , were deaminometribuzin and diketometribuzin. The anodic wave observed after electroreduction is associated with the oxidation of the methylthiolate generated in the electrolytic process. This wave was used to quantitatively determine metribuzin in a commercial sample by anodic stripping voltammetry. The electro-Fenton method was employed to promote decontamination by eliminating the herbicide, resulting in 80% of mineralization of the metribuzin.

Determination of Metribuzin with a Cobalt Phthalocyanine-Modified Carbon Paste Electrode

“…The pH was studied between 2.0 and 8.5 (using a 0.08 mol L −1 Britton-Robinson buffer solution) and the cobalt phthalocyanine composition between 7 and 20% (m/m). The best response was obtained with pH 2.0, which is compatible with the literature values (Lima et al 2009;Janíková et al 2016) and applying a potential of −690 mV and cobalt phthalocyanine composition of 15% (m/m) (data not shown). The response of the sensor under optimized conditions is shown in Figure 5, and the corresponding analytical curve (inlay of Figure 5) showed a linear response to metribuzin with concentrations up to 2.0 � 10 −4 mol L −1 , a sensitivity of (15 � 4) � 10 4 μA L mol −1 , r 2 greater than 0.999, and limits of detection and quantification of 5.30 � 10 −6 (1.14 mg L −1 ) and 17.7 � 10 −6 mol L −1 (3.79 mg L −1 ), respectively.…”

“…As is seen in Table 1, results indicate recoveries close to 100%. In comparison with other sensors in the literature, the developed sensor has the advantage of being mercury-free (Ludvík et al 1998;Skopalová et al 2001;Janíková et al 2016) and holds similar sensitivity to other carbon-based electrodes (Lima et al 2009;Moreno et al 2009;Stojanovic et al 2016). 44, 4.76, 6.98, 9.09, 11.1, 13.0, 14.9, 16.7, 18.4, and 20.0 � 10 −5 mol L −1 metribuzin.…”

“…To avoid the drawbacks of these methods, like cost, time, and lack of portability, electrochemical alternatives can be a suitable option (Vyskočil and Barek 2009). Recently, Stojanovic et al (2016) briefly reviewed the published electroanalytical methodologies; not surprisingly, initial methods included the use of pure mercury electrodes (de Erenchun et al 1997;Ludvík et al 1998;Ludvík and Zuman 2000;Skopalová et al 2001;Skopalová and Navrátil 2007); more recently, carbon (Lima et al 2009), bismuth (Moreno et al 2009;Tutunaru et al 2015), amalgam (Janíková et al 2016), polymer (norvaline) film (Jia et al 2016), and thin-film mercury-based (Stojanovic et al 2016) electrodes have been applied. The use of chemically modified electrodes based on carbon paste is attractive, mainly due to the simplicity and low cost of paste preparation.…”