Desenvolvimento e validação de método utilizando SPE E GC-MS para a determinação multirresíduo de pesticidas em água potável

Abstract

The water resources contamination has caused great environmental impact worldwide. In Brazil, the Ministry of Health through the Law 518 defines potability parameters, between them, the maximum limits for a list of pesticides. In this work it was developed and validated a method for a pesticide determination in drinking water using gas chromatography coupled with mass spectrometry in selective ion monitoring mode (GC-MS-SIM). In the chromatographic separation a HP-5MS (30 m x 0.25 mm id x 0.25 μm) column was used, with a total analysis time below 30 min. In agreement of the concentration level demanded in the determination of some pesticides, in the ng L-1 order, a concentration factor of 400 times was necessary, carried through a solid phase extraction (SPE). After an initial evaluation with different sorbents and solvents, the cartridge Strata X® of 30 mg/3 mL and dichloromethane for the elution were selected. During the method development, optimizations were carried out through factorial models for evaluation of variable effects to the sensitivity and the extraction step. The method validation involved all the usual parameters of internal validation including detection and quantification limits, precision (instrumental precision, repeatability and intermediate precision), accuracy (recovery), linearity, selectivity, robustness, uncertainty of measurement, practical reporting limit and range of application. The gotten results had presented limits of instrumental quantification between 1 and 37 μg L-1 and method reporting limits between 0.003 and 0.093 μg L-1, attending the legislation limits. Only three compounds had presented recoveries below 50% (hexachlorobenzene, aldrin and permethrin). The others presented average recoveries between 51 and 116%. Although the differentiated chemical nature of the analyzed pesticides becomes difficult a good recovery for all the evaluated compounds, the intermediate precisions had guaranteed excellent results being well below of the Horwitz curve. Correlation factors between surrogate standards and pesticides allow the correction of recovery values in the samples, supplying more accurate results. In the robustness study, the method demonstrated to be consistent to external changes having to be taken a special attention to be solvent evaporation step before redissolution. Through the uncertainty estimate was possible to verify that the main sources are the repeatability, the evaporations and the sample turbidity. The analyses in real samples had satisfied the criteria of instrumental qualification and system suitability. The method selectivity has been considered in agreement and evaluated through the relative recovery of quantification and qualification ions. The method has been considered fitness for purpose and in compliance with the quality demanded by the ISO IEC 17025.