Full Collision Energy Ramp-MS2 Spectrum in Structural Analysis Relying on MS/MS.

Abstract

Albeit frequently being overlooked, MS2 spectrum variation against collision energy (CE) implies auxiliary structural clues for m/z values. Online energy-resolved MS (ER-MS) provides the opportunity to acquire the trajectory of ion intensity against CE for any fragment ion of interest, thus exactly offering the desired momentum to empower the conventional MS2 spectrum at a certain CE forward to a full-CE ramp MS2 spectrum (FCER-MS2). Efforts were made here to construct an FCER-MS2 spectrum and to evaluate its potential toward structural analysis. Flavonoids were employed as a proof of concept. MS2 spectra of 76 compounds were recorded by LC-Q-Exactive-MS, and online ER-MS was subsequently programmed using LC-Qtrap-MS to build a breakdown graph for each obvious fragment ion. After defining the greatest value amongst all regressive apices as 100%, the normalized breakdown graphs comprised an FCER-MS2 spectrum for each compound. The FCER-MS2 spectrum contained the MS2 spectrum at any CE as well as optimal CE (OCE) and maximal relative ion intensity (RIImax) of each fragment ion. Except the pronounced isomeric discrimination potential, either OCE or RIImax reflected certain structural properties, such as aglycone, glycosidic bond, and hydroxy, methoxy, and glycosyl substituents. These rules were subsequently applied for flavonoid-focused characterization of a famous herbal medicine, namely Scutellariae Radix, and high-level structural annotation was accomplished for 75 flavonoids. Above all, the FCER-MS2 spectrum includes m/z, OCEs, and RIImax features, thus facilitating confidence-advanced structural analysis.