False Positive Identification of Pesticides in Food Using the European Standard Method and LC-MS/MS Determination: Examples and Solutions from Routine Applications  
[PERSON]  
1 Balint Analitika Ltd., Fehrevari (tm) 144, 1116 Budapest, Hungary 1  
[PERSON]  
1 Balint Analitika Ltd., Fehrevari (tm) 144, 1116 Budapest, Hungary 1  
[PERSON]  
1 Balint Analitika Ltd., Fehrevari (tm) 144, 1116 Budapest, Hungary 14 Correspondence: [EMAIL_ADDRESS]; Tel. : +36-1-455-4010414  
should not deviate from that one in the calibration within a tolerance limit of \(\pm\)0.1 min. If the peak shape distortion is caused by the matrix and not by an interfering peak, a larger retention time shift may be acceptable in case the method includes the corresponding isotopically labelled internal standard whose peak shape is also distorted [19]. The IR is calculated as the response ratio of the qualifier (less intense ion trace) and the quantifier ion transitions. IR values from sample extracts should be within \(\pm\)30% of the average of the calibration standards from the same sequence [19]. Even though the identification criteria listed above are appropriate, false identifications have been reported in certain cases [20; 21; 22; 23]. This links to the high number of pesticide/commodity combinations. The analysis of hundreds of pesticides in foods with rather different matrices (hydrophilic/lipophilic) could lead to wrong qualification of certain pesticides using GC-MS or LC-MS detections. Using high resolution MS (HRMS) [PERSON] et al. (2011) detected nine false positives per sample when employing LC-QTOF-MS (time-of-flight mass spectrometry) [20]. [PERSON] et al. (2012) also addressed LC-HRMS to screen pesticides in food; when only the retention time (\(\pm\)30 s) and one diagnostic ion (mass accuracy tolerance of \(\pm\)5 ppm) were used for identification, the number of false positives were between 19 (bell pepper) and 41 (white cabbage) [21]. Overall, 128 pesticides (e.g., diethyltoluamide, isoprocarb, metolcarb, pyrethrin I, and trimethacarb) were falsely detected in the total of 21 commodities. The relative response thresholds or the second diagnostic ion could improve the identification. As for the secondary ion, the A + 1 or A + 2 isotope for chlorinated and brominated pesticides may all be suitable options [21]. [PERSON] et al. (2009) reported the false identification of sebuthylazine in a tarragon sample by LC-MS/MS (triple quadrupole) technique using two ion transitions and their IR for identification at the expected retention time of sebuthylazine [22]. The application of a third ion transition for MS/MS detection, GC-MS analysis and LC-TOF-MS could appropriately show that the identified compound was actually nepellitoring [22]. In 2015, a collaborative study on LC-MS/MS identification reported that it is indeed not supported to apply relative tolerances for retention time values, and to set different tolerances for ion ratios depending on the relative abundance of the two measured product ions. Absolut retention time shift of \(\pm\)0.1 min is acceptable and IR deviations are typically within \(\pm\)20% (relative). This was concluded from as many as 135,000 manually verified chromatograms [23]. False identification with GC-MS was also published recently. Earlier, delta-hexachlorocyclohexane was detected in tobacco [11], and only multidimensional (that is, more expensive) separation could verify that this analyte was not present in the sample over the limit of detection. In our laboratory, we address the LC-MS/MS technique on a daily basis to cover 480 pesticides in various foods of plant origin [24] accredited to EN 15662:2018 [18]. These food matrices include mainly everyday fruits and vegetables, but also some less common foods, such as date seed coffee, dried ginger, elderberry, herb extracts, peppercorn and fennel.