Advantages of external accumulation for electron capture dissociation in Fourier transform mass spectrometry

A combination of external accumulation (XA) with electron capture dissociat ion (ECD) improves the electron capture efficiency, shortens the analysis t ime, and allows for rapid integration of multiple scans in Fourier transfor m mass spectrometry, This improves the signal-to-noise ratio and increases the number of detected products, including structurally important MS3 fragm ents. With XA-ECD, the range of the labile species amenable to ECD is signi ficantly extended. Examples include the first-time determination of the pos itions of six GalNAc groups in a 60-residue peptide, five sialic acid and s ix O-linked GalNAc groups in a 25-residue peptide, and the sulfate group po sition in a Ii-residue peptide. Even weakly bound supramolecular aggregates , including nonspecific peptide complexes, can be analyzed with XA-ECD, Pre liminary results are reported on high-rate XA-ECD that uses an indirectly h eated dispenser cathode as an electron source. This shortens the irradiatio n time to greater than or equal to1 ms and increases the acquisition rate t o 3 scans/s, an improvement by a factor of 10-100.