Eletrodo de pasta de carbono modificado com ftalocianina de ferro para a determinação de carbaril em águas para consumo humano

Abstract

A new low cost simple electrochemical sensor was prepared by modification of the iron phthalocyanine carbon paste CPE–FePC for the indirect determination of carbaryl in drinking water. Usually, carbaryl oxidation does not occur, may occur slowly, or potentially occurs outside the working potential window of the electrode. However, the determination of 1- naphthol methylcarbamate, the main product of carbaryl hydrolysis, enables the indirect determination of carbaryl. The hydrolysed form is the main non-biological degradation pathway of carbaryl in natural waters. The Brazilian National Environment Council allows a maximum carbaryl value of 0.02 μg L-1 in freshwater, class 1 and 2, and 70 μg L-1 for class 3 and a limit of 0.32 μg L-1 for freshwater saline and brackish waters. The electroanalytical techniques are an alternative to the most used chromatographic techniques, because they have low acquisition cost and high analytical sensitivity. The preparation of the working electrode involved the mixture of graphite powder, iron phthalocyanine and mineral oil, being studied electrodes containing from 1 to 3% (m m-1 ) of FePC. The electrode was submitted to electrochemical studies using the cyclic voltammetry (CV) and square wave (SWV) techniques, being performed studies of pH and optimization of the electrochemical parameters. The highest analytical response of 1-naphthol methylcarbamate was recorded for the electrode containing 1% FePC, significantly higher than that obtained for the unmodified carbon paste CPE electrode. Also, higher percentages of 1% FePC resulted in a decrease in electric current intensity. Using cyclic voltammetry, only a 0.54 V oxidation peak was observed indicating that this may be an irreversible process. For the study of pH in Britton Robson support electrolyte 0.1 mol L-1 (pH 1.8 to 10), pH 4.5 was chosen because it has higher analytical sensitivity. From the experimental VOQ parameters studied, we chose: 60 s-1 frequency, 50 mV pulse amplitude and 6 mV potential increment. The linear range was from 72.08 μg L-1 to 457.02 μg L-1 , detection limit of 1.63 μg L-1 and quantification of 4.94 μg L-1 . The studies indicated high analytical sensitivity for 1-naphthol methylcarbamate in CPE– FePC, proving the feasibility of indirect determination of carbaryl in water by SWV.