Glyphosate is a systemic, post-emergent, non-selective herbicide widely used in agriculture. The objective of this study was to develop a method for sample preparation, to partially purified natural water samples contaminated with residues of glyphosate, and to quantify them by derivation and spectroscopically. To assess the accuracy of the method, samples of water from an artesian well and from a stream were fortified with known amounts of glyphosate. The concentration of glyphosate was determined using a standard curve concentration range from 4 to 14 mg L -1. From the concentration of glyphosate recovered, in both samples of fortified water it was found that DOWEX MWA -1 resin and NaCl 0.100 mol L -1 eluent were effective in the purification of the samples. It was found that the method is reproducible because the results are within the range acceptable for the analysis of residues of pesticides, with a percentage coefficient of variation below the allowed limit. It was found that in the water samples with suspected contamination, the concentration of glyphosate was greater than that permitted by the Ministry of Health. Index terms:Residues, spectroscopic studies, systemic herbicide. RESUMOO glifosato é um herbicida sistêmico, pós-emergente e não seletivo largamente utilizado na agricultura. Neste trabalho, objetivou-se desenvolver um método para preparação de amostragem, purificar parcialmente amostras de água natural contaminadas com resíduos de glifosato e quantificar por derivação e espectroscopicamente. Para avaliar a precisão do método, amostras de água de poço artesiano e de um córrego foram fortificadas com quantidades conhecidas de glifosato. O teor de glifosato foi determinado a partir de uma curva padrão na faixa de concentração de 4 -14 mg L -1. A partir dos teores de glifosato recuperado, em ambas as amostras de água fortificada, constatou-se que a resina DOWEX MWA -1 e o eluente NaCl 0,100 mol L -1 foram eficientes na purificação das amostras. Verificou-se que o método é reprodutível, pois os resultados encontram-se dentro da faixa aceita para análise de resíduos de pesticidas, com coeficiente de variação percentual, abaixo do limite permitido. Constatou-se que nas amostras de água, com suspeita de contaminação, o teor de glifosato foi superior ao estabelecido pelo Ministério da Saúde. Termos para indexação:Resíduos, estudos espectroscópicos, herbicida sistêmico.

This paper shows an application of a first generation porphyrin, FeTPPCl 5,10,25,20-tetraphenylporphyrin iron(III) chloride (FeTPPCl or FeTPP þ ) immobilized on a inorganic matrix, SiO 2 /Nb 2 O 5 (niobium oxide grafted on silica gel surface, designated as SiNb) to the preparation of a carbon paste electrode (CPE). The carbon paste modified with a FeTPP þ immobilized on SiO 2 /Nb 2 O 5 (SiNb), designated as CPE/SiNb/FeTPP, was applied for simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA). Because of the overlapping of the voltammetric peaks of DA and AA, the multivariate calibration methodology based on partial least square regression (PLSR) was proposed. The data pre-treatment used in this process was mean centering and to choose the principal components number a cross validation procedure was used (leave-one-out). Five principal components were necessary to obtain the lowest PRESS (prediction residual error sum of squares). The statistics showed that this model explains approximately 95.2% of the variance from the data set. Using this model, high correlation between actual and predicted concentrations was observed, mainly for higher dopamine (maximum relative error of 8%) and ascorbic acid (maximum relative error of 10%) concentrations. For low analytes concentrations the relative error increases to 35% for AA. Considering the similarity of the voltammetric response of the analytes, the results obtained were satisfactory and showed the promissory capability of the CPE/SiNb/FeTPP coupled multivariate calibration methods for simultaneous voltammetric analysis of DA and AA.

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