Development of QuEChERS extraction method for the determination of pesticide residues in cereals using DART-ToF-MS and GC-MS techniques. Correlation and quantification study

Abstract

Cereal crops comprise more than 60 % of agricultural production worldwide. To ensure high production, the extensive use of pesticides is common practice. Analysis of pesticide residues in food and particularly cereals has become an essential requirement for consumers, producers, food inspectors and authorities. However, the determination of pesticides in cereal samples is not an easy task due to the complexity of the matrices and the trace levels of pesticides. In this study, a simple and high-throughput method was validated for the determination of multi-residue pesticide in 30 different types of cereals which are commonly consumed around the world. QuEChERS procedure has been developed, a mixture of primary-secondary amine and C18 proved better performance for the reduction of the interfering substances from the cereal grains than multiwalled carbon nanotubes. For a comprehensive investigation, the pesticide cereals contents were purified following the established cleanup method and detected by DART-ToF-MS and GC-MS. As “soft” and “hard” MS ionization methods, DART-ToF-MS and GC-MS are strong nominated for comprehensive studies of the unknown molecules. The results showed that 19 pesticides were successfully identified by both techniques in all samples, 16 by DART-ToF-MS and 13 using GC-MS. Regarding the correlation between the developed methods, 10 pesticides were detected as a commonality between the two techniques, this indicates that a single MS technique is not sufficient to detect all of the existing pesticides in cereals. The findings exposed that the two MS techniques are complementary, and both can be used for comprehensive identification of the pesticides presented in cereals. Quantitative analysis was performed using GC-MS under the selective ion monitoring mode by external and internal standard methods. Tributyl phosphate has been used as an internal standard. The measured limits of detection ranged between 4 and 9 μg kg−1 for all pesticides, while the limit of quantification values was <34.8 μg kg−1, which were below the regulatory maximum residue limits. The coefficient of determination was >0.9980 within the calibration linearity range of 15–6250 μg kg−1 for the detected pesticides. The recovery of all detected pesticides was in the range 75.28–122.02 % (n = 3) with associated RSDs <14 % indicating satisfactory accuracy.