Sandwich injection and analyte protectants as a way to decrease the drift due to matrix effect between bracketing calibration in GC-MS/MS: A case study
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abstract
In pesticide residues analysis, the drift is the difference between the concentration of two bracketing calibrations in the same batch. According to the SANTE/12682/2019 guideline a criterion of ±30% must be met or positive samples should be reanalyzed. This study aimed to investigate, for the first time, the efficiency of using analyte protectants (Aps) and the sandwich injection approach (SIA) to eliminate the drift between bracketing matrix matched-calibrations taking strawberry as an example. The strawberry samples were prepared according to the citrate-buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure, followed by solvent exchange from acetonitrile to n-hexane:actone (9:1). Two batches were injected with the same sequence on GC-MS/MS, the only difference was that the first batch was without Aps and the second was with Aps. The sequence of the batch was as follows: blank solvent injection, 5 strawberry matched-calibrations at 0.05 μg/ml, separated by 20 blank strawberry injections after each strawberry matched-calibration injection. The drift was measured by considering the results of the first calibration as 100% and comparing the rest 4 injections with it. After 20 injections, out of the studied 219 pesticides, more than half of the pesticides fell out of criteria when analyte protectants were not used, and by the end of the samples batch 95% of the analytes were out of criteria. Only 8% of the studied analytes were out of criteria for the Aps batch after 20 injections. In the end of the 80 samples batch, 17% were out of criteria. Furthermore, at the end of the protected matrix-matched calibration batch, 90% of the pesticides had an RSD less than 15% in comparison with only 5% of the analytes for the non-protected batch. Moreover, the non-protected batch had an obvious negative drift in comparison with the protected batch. For example, the number of pesticides that had a lower result in the second matrix matched-calibration for the non-protected batch was more than twice the number in the protected batch (194 compared to 91 out of 219 pesticides for both experiments).
