Integration of offline two-dimensional chromatography and mass defect filtering-based precursor ion list data acquisition for targeted characterization of diterpenoid alkaloids in the lateral roots of Aconitum carmichaelii

The hyphenated technique of offline two-dimensional (2D) chromatography with high resolution mass spectrometry (MS) was an efficient tool for separation and characterization of components in complex systems such as herbal medicines, especially those co-eluting components or isomers. In this study, we constructed the ultra-performance convergence chromatography (UPC2) × reversed phase (RP) chromatographic separation system and developed a mass defect filtering (MDF)-based precursor ion list (PIL) acquisition method to improve the selectivity and sensitivity of this technique, and the systematic characterization of diterpenoid alkaloids in the lateral roots of Aconitum carmichaelii (namely "Fuzi" in Chinese) was used as an example. The constructed offline 2D separation system showed a good orthogonality of 0.77. Besides, the in-house databases for known and predicted C19- and C20-diterpenoid alkaloids were established by molecular design in Compound Discoverer software for MS data matching and filtering, and two MDF windows were further constructed to screen out more potential diterpenoid alkaloids with novel structures and to obtain the PIL (mass range: even values between 298 and 1020 Da, parent mass width: ±100 mDa) for data acquisition by calculating the m/z values of potential ions using mass range and corresponding mass defect in the MDF windows. In addition, an integrative structure interpretation strategy was developed by integrating elemental composition analysis, ring double bond analysis, neutral loss filtering, diagnostic ion filtering and database matching, etc. As a result, a total of 659 components in the lateral roots of A. carmichaelii were exposed and characterized, including 526 potential new compounds. This strategy showed significant advantages in improving the coverage and selectivity of screening, and could also be applied in systematic characterization of components in other herbal medicines.