An Ion Mobility/Ion Trap/Photodissociation Instrument for Characterization of Ion Structure

A new instrument that combines ion mobility spectrometry (IMS) separations with tandem mass spectrometry (MSn) is described. Ion fragmentation is achieved with vacuum ultraviolet photodissociation (VUV PD) and/or collision-induced dissociation (CID). The instrument is comprised of an approximately 1 m long drift tube connected to a linear trap that has been interfaced to a pulsed F-2 laser (157 nm). Ion gates positioned in the front and the back of the primary drift region allow for mobility selection of specific ions prior to their storage in the ion trap, mass analysis, and fragmentation. The ion characterization advantages of the new instrument are demonstrated with the analysis of the isomeric trisaccharides, melezitose and raffinose. Mobility separation of precursor ions provides a means of separating the isomers and subsequent VUV PD generates unique fragments allowing them to be distinguished.