Multistage Tandem Mass Spectrometry Using an Electron-Activated Dissociation Device with a Linear Ion Trap and...

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.