Desenvolvimento de método para determinação de paraquate, diquate, clormequate e mepiquate em cevada e trigo utilizando HILIC-UHPLC-MS/MS

Abstract

Quaternary ammonium compounds (QUATs) constitute an important class of agrochemicals that include paraquat, diquat, chlormequat and mepiquat. Among these, paraquat is one of the most well-known herbicides in the world, both for its efficiency and its toxicity. These factors increase the need to monitor the residues of these pesticides that can remain in food. In this research, a method was developed for determination of these four compounds in barley and wheat samples using hydrophilic interaction liquid chromatography (HILIC) with ultra-high-performance liquid chromatographic tandem mass spectrometry (UHPLC-MS/MS). Conditions of the UHPLC-MS/MS system were evaluated and the selection of the mobile phase was performed from a central composite planning. The extraction step was evaluated through tests using different solvents, mode and time of contact of the extraction solvent with the sample and comparing the use of dry and slurry samples. For the cleaning of the extracts three steps were evaluated: partition with dichloromethane, use of sorbents and addition of acetonitrile to the extract. In this step, the optimization of the sorbents was carried out from an experimental design. The proposed procedure consisted of the extraction of 10 g of slurry with 5 mL of ultrapure water and 5 mL of methanol with 1% (v/v) formic acid, and cleaning the extracts by partitioning the supernatant with dichloromethane (3:1.5 v/v), dispersive solid phase extraction (d-SPE) with chitosan and use of acetonitrile (1:1, v/v). The validation of the method presented satisfactory results of selectivity, linearity, accuracy and precision. Quantification of the analytes employing the curve by dilution of the spiked blank compensated for the strong matrix effect and recovery values for all compounds in both matrices. The proposed method is suitable for the determination of paraquat, diquat, mepiquat and chlormequat in barley and wheat and was applied with efficiency in 20 samples of barley and wheat, demonstrating the applicability of the method in routine laboratory analysis.