Desenvolvimento de método eletroquímico para determinação de glifosato em presença de simonkolleite e dopamina

Abstract

Glyphosate (GLI) is a pesticide used around the world that has characteristics such as low cost, high efficiency and viability in different cultures. However, it also offers potential damages to health, being essential its determination and monitoring in environmental matrices, however, its quantification involves high cost. The objective of this work is the development of an electrochemical sensor for GLI that combines low cost, easy preparation and sensitivity. GLI does not present an electrochemical signal, aiming at indirect detection, its interaction with dopamine (DOPA) was evaluated by UV-vis, infrared (FTIR) and electrochemical spectroscopy. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were used for electrochemical determinations, glassy carbon electrode (GCE) and this modified with multiwalled carbon nanotube (GCE-MWCN), the best medium was evaluated. for analysis (buffers: acetate pH=4.5; phosphate pH=7; borate pH=10). Aiming to gain sensitivity to the system, the use of simonkolleite nanoparticles (SK) was analyzed, in addition to SK containing Ag: 0.1% and 1%, of which, it was observed that the use of SK presented better results, thus, the best ratio between SK and DOPA was evaluated to obtain a more sensitive system. The system was evaluated for the presence of the following interfering species: Ca2+, Mg2+ and Cu2+, in concentrations that varied from 6 to 600 ppb, in GLI (7 ppb), the method was also used for analysis of a soil sample fortified with GLI. The use of DOPA proved to be viable, and a mechanism for the interaction involved was proposed. The use of GCE electrode showed adsorptive mass transport, being relevant the modification with MWCN, regarding the use of different pH ranges, the use of pH=7, presented greater sensitivity, making it the best option among the evaluated ranges. The use of SK provided greater sensitivity to the system, while the use of SK containing Ag promoted a reduction in signal intensity, the use of a 1:1 ratio between DOPA and SK allowed greater sensitivity to the system, without interfering in the assessment of GLI. The use of GCE-MWCN electrode in phosphate buffer pH = 7.00, DPV, DOPA (2 ppm) and SK (2 ppm), provided obtaining a method with linear range of GLI response from 1 to 7 ppb. The system demonstrated repeatability and linearity (R = 0.9937), obtaining LD and LQ of 0.1971 ppb and 0.6571 ppb, respectively. As for the evaluation of the interfering species, interference in the analytical signal of up to 13% (Ca2+), 2% (Cu2+) and 4% (Mg2+) was observed, revealing a satisfactory result in relation to other electrochemical methodologies. The method allowed the detection of GLI in a fortified soil sample, observing the presence of 6,894 ppb, it was validated using a method that involves spectroscopy in the visible region, presenting means that do not differ statistically (T Student 95%). presenting itself as a promising proposal of low cost and easy preparation in the evaluation of GLI in environmental samples.