The Improved Method of Sample Preparation for the Gas Chromatographic Determination of the Residues of 69 Pesticides in Winter Wheat Grain

Mikhail Zayats, The Laboratory of Dynamics of Pesticides, RUE “Institute of Plant Protection”, a/c Priluki, Minsk distr., Republic of Belarus
Sergey Leschev, Analytical Chemistry Department, Belarusian State University, Faculty Of Chemistry, Minsk, Republic Of Belarus

The possibility of multi-residue determination of pesticides in grain of cereals at or below maximum residue levels (MRLs) by chromatographic methods is often determined by the efficiency of the preliminary sample preparation. Currently the most popular sample preparation techniques have such drawbacks as multistage of the process, consumption of expensive reagents, high dilution of extracts, low efficiency and selectivity of extract purification steps.

To overcome such problems the improved method of determination of residues of 69 pesticides of different classes (amides, anilinopyrimidines, carbamates, carbanilates, dinitroanilines, imidazoles, morpholines, neonicotinoids, organodithiophosphates, organothiophosphates, pyrethroids, simm-triazines, esters, strobilurins, thiocarbamates, triazoles, etc.) in winter wheat grain by gas chromatography with mass spectrometric detection was developed and validated. The technique is based on acetonitrile extraction from wetted milled grain in presence of NaCl and K₂CO₃ with subsequent evaporation of extracts. The developed extraction method of sample preparation is simple, quick, consumes only cheap and rather common reagents and provides extracts clean enough to obtain reproducible quantitative results without cleaning of injector liner at least at 200 injections. The recovery values of studied pesticides from winter wheat grain were between 76 and 118 % with RSD values below 9 % at 10.0, 20.0 and 200 µg·kg^-1 spiking levels. Limits of detection were less or equal to 0.01 mg·kg⁻¹ for all the studied pesticides. Limits of quantification were below or equal to the MRLs, which were set in Belarus and in the European Union countries for the corresponding pesticides in wheat grain. The linear range used in the calibration curves was from 50 to 3000 µg·L^-1 with the values of the determination coefficients R² more than 0.997. The developed method was successfully used for the analysis of cereals for the residues of the pesticides, which were under registration trials held in Belarus in 2015-2016.