An enhanced approach for targeted multi-residue screening of pesticides in complex herbal medicines by ultra high-performance liquid chromatography tandem ion mobility/quadrupole time-of-flight mass spectrometry

Recently, serious concerns have been raised about potential safety risk posed by exogenous pesticide contaminants in herbal medicines. It is highly desirable to have reliable detection and determination of suspected pesticide residues for understanding of their overall quality. However, inherent metabolites abundant in herbal medicines typically make screening of trace-level pesticide residues arduous. Taking Lonicerae Japonicae Flos (LJF) as an example, the current study investigated the capability of a three-dimensional separation system, ultra high-performance liquid chromatography tandem ion mobility/quadrupole time-of-flight mass spectrometry (UPLC-IM/Q-TOF MS), for qualitative detection of numerous pesticides when suffering from complex matrix interferences. The comparison of collision gases was first performed to improve unwanted dissociations of pesticides, particularly labile ones, and nitrogen was ultimately chosen instead of argon. Further optimization of key MS parameters resulted a data-independent high-definition MSE (HDMSE) method was developed. Then, an in-house pesticide scientific library (PSL) containing 438 pesticides was constructed following a four-step workflow. Based on multi-dimensional information in this library, different identification criteria were compared and an enhanced qualitative screening approach for 432 targeted pesticides was finally proposed and validated. By its application to 104 batches of LJFs, the approach was demonstrated effective in resolving complex matrix interferences. Moreover, collision cross section (CCS) for identification purpose was favorable to improve detection sensitivity while maintain ideal accuracy.