Comprehensive profiling of Stephania tetrandra (Fangji) by stepwise DFI and NL-dependent structure annotation...

Stephania tetrandra S. Moore, a widely used traditional antirheumatic herbal medicine (HM), is a rich source of isoquinoline alkaloids. With the exception of the two recognized isoquinolines, viz. tetrandrine and fangchinoline, the other isoquinoline alkaloids present in S. tetrandra have not been clearly clarified. In addition, due to their similar names and morphological similarities, S. tetrandra is often mistakenly substituted and adulterated with the nephrotoxic Aristolochia fangchi. In this study, ultra-high-performance liquid chromatography-triple time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) was initially employed to comprehensively profile the isoquinolines from S. tetrandra. To overcome the complexities arising due to the similar mass behaviors of the isoquinolines, a stepwise diagnostic fragment ion (DFI) and neutral loss (NL)-dependent structure annotation algorithm was proposed, and this accelerated the identification of 393 isoquinolines distributed over twenty classes. Consequently, liquid microjunction surface sampling-high-resolution mass spectrometry (LMJ-HRMS) was deployed in an attempt to directly authenticate S. tetrandra by the chemical profiling of its crude slice. By matching the 393 isoquinolines, the 87 peaks detected by LMJ-HRMS were assigned to 270 isoquinolines, including the recognized tetrandrine and fangchinoline. The absence of aristolochic acid-related mass signals confirmed the authentication of S. tetrandra. In summary, LMJ-HRMS can be considered a direct, nondestructive, high-throughput, and environment-friendly analytical method for the authentication of HMs. Moreover, the stepwise DFI- and NL-dependent structure annotation algorithm-based UHPLC-Q-TOF-MS method allowed high-coverage detection and high-quality data processing of the inherent structural similarity and complexity of isoquinolines or other phytochemical compounds.