Otimização e validação de método individual para determinação de diquate e paraquate por UPLC-MS/MS em feijão-caupi

Abstract

In this study, a method for determination of diquat and paraquat in Cowpea was optimized and validated. In order to obtain a good homogeneous sample, the Cowpea were milled and then prepared a slurry of matrix and water (ratio 1:1.5; m/m). The extraction procedure was based on the QuPPe-Method and modifications of the method were developed. As extraction solution, it was used methanol containing hydrochloric acid 5 mol L-1 (6:4 v/v) plus isotopically labeled (IL) analogues of the targets analytes, which were used as internal standards (ISTDs). In order to promote a better extraction, the mixture between slurry plus extraction solvent was manually shaked for 2 min, vigorously, and then taken to a water bath, at 80°C, for 15 min. After, the mixture was cooled down to room temperature and then centrifuged for 4 min at 4000 rpm. The supernatant was used for the analysis. All analytical solutions of diquat and paraquat have been prepared and stored in polypropylene vessels. The determination of diquat and paraquat was done into a liquid chromatographic system coupled to a tandem mass spectrometer (UPLC-MS/MS). The validation was performed by analyzing spiked samples at three different concentrations (10, 20 and 50 μg kg-1), with seven replicates (n = 7) for each concentration. Assessed, both as to diquat and paraquat, was determined the linearity (r) of analytical curves, accuracy (as recovery %), instrument and method limits of detection and quantification (LOD and LOQ), precision (as RSD %) and matrix effects (%). In the recovery study of Diquat, the average recovery obtained was between 77 and 85% with RSD% values ≤ 20%, for all 3 spike concentrations. On the other hand, paraquat presented averages between 68-103% and averages of RSD between 14.4-25.4 %. The LOQ of the method was 10 and 20 μg kg-1 for diquat and paraquat, respectively. The matrix effect was present for both pesticides even using isotopically labeled (IL) analogues of the target analytes, which were used as internal standard (ISTD), therefore requiring matrix-matched calibration standards for application in routine analysis. This study was applied for samples from EMBRAPA study.