Agrotóxicos em doces de frutas em pasta: determinação de resíduos por μLC-QTRAP-MS/MS e estudo de estabilidade

Abstract

This work presents multi-method for pesticide residues determination in fruit jams. Slurries of the fruit jams and ultrapure (u.p.) water were prepared to yield homogeneous samples and to facilitate the sample handling. The modified QuEChERS method was used for the sample preparation. Due the high detectability of the micro flow liquid chromatography triple quadrupole-linear ion trap mass spectrometry equipment (μLC-QTRAP-MS/MS) and to minimize the matrix effect (%) the acetonitrile extracts were diluted 30-fold before analysis. The method validation was performed analyzing spiked samples at the concentrations of 9 and 45 μg kg-1 (n=5). The method met validation criteria of 70 120% recovery and relative standard deviation (RSD) ≤ 20% for 93% (99) of the 107 pesticides evaluated. The reporting limit (RL) was 9 and 45 μg kg-1 for, respectively, 66% and 26% of the analytes, 5% of the compounds did not fulfill the requirements for validation and 3% were not detected at the studied concentrations. The validated method was applied to the analysis of 51 different fruit jam samples from Brazil and from Spain. Pesticide residues were detected in 80% of the samples, 51% of which contained at least one pesticide at concentration higher than 10 μg kg-1. Moreover, the stability of five pesticides was evaluated in the preparation of home-made fruit jams from spiked fruits. Thereunto, five types of fruits (orange, apple, strawberry, pear and peach, with n=2 for each type of fruit) were grinded and spiked at 500 μg kg-1 with a mixture of carbendazim, chlorpyrifos, imidacloprid, iprodione and propargite. Home-made jams were prepared with these spiked samples by cooking, over medium heat, the grinded spiked fruit with sugar and u.p. water (ratio, 5:5:2, w/w/w), in an open pan for 30 min. The modified QuEChERS extraction method was applied either to blank fruits, to the fruits spiked at 500 μg kg-1 and to the home-made jams (prepared from spiked fruits at 500 μg kg-1). The extracts of home-made jams and blank fruits were analyzed by liquid chromatography quadrupole-time of flight mass spectrometry (LC-QTOF-MS) to ascertain the occurrence of the known metabolites of the spiked pesticides and to determine the number of co-extracted matrix components from the fruits and from the jams. All samples were also analyzed by μLC-QTRAP-MS/MS for estimation of the pesticides processing factors. So the pesticide concentrations found in the spiked fruits were compared to the concentrations found in the home-made jams (pesticide concentration measured in the jams/pesticide concentration measured in the raw fruits).