Oli Hale (@olijhale.bsky.social)

Multistage Tandem Mass Spectrometry Using an Electron-Activated Dissociation Device with a Linear Ion Trap and Structural Identification of Cardiolipins We have developed an electron-activated dissociation (EAD) device with product isolation functionality for multistage tandem mass spectrometry (MSn). The EAD portion is a branched magneto-radio frequency ion trap with an electron beam source, and we attached a linear radio frequency quadrupole (RFQ) ion trap (or D trap) to one of the branches of the EAD device. Because the D trap was installed inside a strong ring permanent magnet, we made the linear quadrupole rods from para-magnetic stainless steel, which works as a magnetic shield. Using this D trap, we isolated a fragment produced by the first dissociation technique, which can be further fragmented by collision-induced dissociation (CID) or EAD. Using the new EAD-D trap, we demonstrated a near-complete structural identification of cardiolipins via an MS3 workflow with CID followed by electronically excited dissociation (EED) after isolation from the CID products. The number of double bonds, their positions, and cis/trans isomerism in each acyl group, as well as the regioisomerism of acyl chains, were fully identified; however, the only remaining structural ambiguity of the cardiolipins was the chirality at the central carbon of the central glycerol group. We identified 18 cardiolipins in Escherichia coli (E. coli) extract. https://pubs.acs.org/doi/10.1021/acs.analchem.5c05400