Validação de técnicas analiticas para determinação de residuos de pesticidas em vinho

Abstract

Vine is one of the most important crops in Portuguese agriculture. To counteract the effects of various diseases and pests that may occur in vineyards, a great part of the total pesticide consumption in Portugal is dedicated to this crop. Hence, it is of great importance to study the the presence of pesticide residues in wine. Food is the basis of human life, and wine is an important part of a regular diet of populations, as well as one of the most widely consumed beverages. therefore contamination with toxic pesticides leads to severe effects on human health. Thus, it is essential to use control measures and/or reduction of these toxic residues products. Currently, the analysis of pesticide residues in wine is usually done by applying chromatographic methods, mainly by gas chromatography. Spectroscopic methods may also be used and are probably the most used methods for the qualitative and quantitative determination of organic and inorganic compounds. In these respects, this study focused on the validation of analytical methods for the determination of pesticide residues in wine. To this end, five pesticides were selected based on their reported appearance in wine grapes and wines, as well as their toxicological characterization. The performance of a method for determination of dithiocarbamates residues in wines by molecular absorption spectrophotometry was validated based on standards EN 12396-1 and NP EN ISO IEC 17025. Calibrations were performed in the range 0,25 - 1,25 mg CS2/L wine and the statistical parameters were determined by linear regression using Microsoft Excel Data Analysis. An adjustment of experimental points to a first degree polynomial was noted by visual inspection of calibration curve, hence, the response could be considered linear in the work range. The linearity of the method was verified by the Pearson correlation coefficient, a value that was always equal or superior to 0,995, by the random distribution of residual values relative to zero and by the existence of a constant slope and a relatively small intercept (order of -10-2), in accordance with Beer's Law. The sensitivity of the method was demonstrated by the mean standard deviation of the calibration curve, which had a value of 0,06 mg/L. The selectivity of the method was also evaluated by the analysis of blanks of wines and no interference of the matrix was observed. The intermediate precision of the method was shown by the average relative standard deviation of 14 %. To evaluate the accuracy of the method, samples fortified with pesticides at three levels were analyzed. Based on the values obtained from these fortifications, a mean recovery of 93 % could be calculated. The limit of quantification was also tested experimentally and calculated to be 0,4 mg CS2/L wine , with a standard deviation of 19,6 %. These results indicate that the method is in accordance with the requirements of document SANCO/10684/2009, which applies to pesticide residues analysis in food and feed. __________________________________________________________________________ v Seventeen samples of different wines were analyzed and no residues of dithiocarbamates were detected. For the determination of pesticide residues in wine by gas chromatography it is necessary to extract them first to an organic phase. This sample preparation is very time consuming and occupies over 80% of the total analysis time. Subsequently the current methods of liquid-liquid extraction and the extraction methods for dispersed solid phase extraction (dSPE) of pesticide residues (chlorpyrifos, dimethoate, metalaxyl and penconazole) were also evaluated in the present study. Results indicated that it appears possible to replace the current methods of liquid-liquid extraction by procedures of dSPE extraction which would imply a great reduction in sample preparation time. Additional studies are needed in these regards, in particular to extend extraction procedures to other analytes and to verify results of these procedures whengaseous or liquid chromatography with mass spectrometer systems are used. It is also important to further study the influence of several factors (e.g. pH, extraction temperatures, temperature program) in both extraction and instrumental analysis methods