Desenvolvimento e validação de método multirresíduo para determinação de pesticidas em arroz polido utilizando método QuEChERS modificado, clean-up dispersivo e GC-MS (NCI-SIM)

Abstract

The rice is the main component of the basic diet of the world-wide population, is therefore, of extreme importance for the food security. In function of this, related aspects its production and comsumption must continuously be monitored and be evaluated, so that its supply is guaranteed. In this study, was development and validated a methodology for determination of residues of 51 pesticides in polish rice grains, using the modified QuEChERS extraction method and Gas Chromatography coupled to Mass Spectrometry with Negative Chemical Ionization and Selected Ion Monitoring (GC-MS NCI-SIM). To that end, previous homogenized rice was spiked with 51 pesticides at 3 different spiking levels (10, 20 and 50 μg kg-1, 6 replicates at each level) and extracted by the modified QuEChERS method. Applying this method, 10 mL of acetonitrile was added to 10.0 g of rice matrix and the tubes were vigorously shaken by hand for 45 s. The tubes were uncapped, 3.0 g of anhydrous magnesium sulfate and 1.7 g of sodium acetate were added, the shaking procedure was repeated and the extract was centrifuged for 8 min. Furthermore, a dispersive clean-up was developed for extract purification. The upper layer (4 mL) of the extracts was transferred to another tube containing 600 mg of anhydrous magnesium sulfate and 500 mg of C18, the shaking procedure was repeated and the extract was centrifuged for 8 min. The extracts were analized by GC-MS NCI-SIM. The method validation was performed of the linear range of the analytical curves (7 concentration levels and 6 injections each), detection limit (LOD), quantification limit (LOQ), matrix effect, as well as precision (as RSD%) and accuracy (as recovery percent). In general, LOD, LOQ and r2 results, obtained from GC, were affected by standards prepared in matrix extract compared to the preparation in solvent. The linear calibration curves was between 1.0 or 2.0 to 100.0 ng mL-1 with r2 values ≥ 0,99. The GC-MS (NCI) allowing the quantification (recovery criteria 70-120% and RSD% values ≤ 20%) of 87% of the target compounds, that showed LOQm of 10 or 20 mg kg-1. Hence, it is possible to conclude, this method proved to be adequate for the multi-residue analysis of pesticides in rice, conciliating sensitivity and acceptable selectivity and all the validation parameters were within the limits suggested for validation of chromatographic methods.