Identification of Phenolic Acid Derivatives in Danshen Using MS³ and MS² Spectra Matching Strategy

"MS/MS spectrum to structure" plays a critical role in the confirmative identification of complicated matrices and is currently regarded as an extremely challenging endeavor. MS/MS information provides vital clues to structural identification. In this study, a strategy was proposed to facilitate unambiguous identification through matching MS3 with MS2 spectra. Initially, MS3 spectra of the featured ions (c and y type ions) generated by the decomposition of ester functional group in esters and the MS2 spectrum of the structural unit ([M -H]-) were all captured on the Qtrap-MS platform equipped with two tandem -in -space collision cells, including the second quadrupole cell (q2) and linear ion trap (LIT) chambers (actually the third quadrupole unit). Subsequently, the MS/MS spectrum matching between MS3 spectra of the ester compound and MS2 spectra of the structural unit(s) were achieved. As a result, the findings corresponding to MS3 and MS2 spectra matching were summarized. Finally, based on HR-MS/MS information of total salvianolic acid derivatives (TSA), 36 kinds of compounds were preliminarily identified through matching with literature information and database retrieval. The applicability of MS3 and MS2 spectra matching strategy was further justified by the confirmative identification of phenolic acid compounds (Rosmarinic acid and salvianolic acid B) in TSA. Above all, MS3 and MS2 spectra matching strategy was quite meaningful towards advancing "MS/MS spectrum to structure" analysis through recognizing and identifying featured fragment ions, and also provided inspiration and new insights for the structural characterization.