Reduction of matrix effects through a simplified QuEChERS method and using small injection volumes in a LC-MS/MS system for the determination of 28 pesticides in fruits and vegetables

A simplified QuEChERS method coupled with a small injection volume was developed for the simultaneous determination of 28 pesticides in 6 matrices (apples, cucumbers, tomatoes, luffa, cabbages, and eggplants) using LC-MS/MS. In the sample procedure, acetonitrile with 0.1% (v/v) formic acid was used to extract and no depurative powder was used. Three fortified levels (10, 50, and 100 μg kg−1) were determined and the recoveries of 168 analyte/matrix combinations were in the range of 60–120% except for cyromazin, pendimethalin, and fenpropathrin. Half of the 168 LOQs were below 0.1 μg kg−1, and 29 LOQs were above 1 μg kg−1. Moreover, four relationships between signal suppression and injection volume were observed ranging from 0.5 μL to 15 μL. For many analyte/matrix combinations, the matrix effects could be reduced to less than 20% if the injection volume was less than a critical value (named critical volume). The critical volume depending on the initial extent of matrix effects was explored and the conclusion was: for weak or medium MEs, usually ≤2 μL injection volume was needed and for several weak MEs, injection volume ≤ 5 μL can reduce the matrix effect to a negligible level.