Ion trap/ion mobility/quadrupole/time of flight mass spectrometry for peptide mixture analysis

An ion trap/ion mobility/quadrupole/time-of-flight mass spectrometer has be en developed for the analysis of peptide mixtures. In this approach, a mixt ure of peptides is electrosprayed into the gas phase. The mixture of ions t hat is created is accumulated in an ion trap and periodically injected into a drift tube where ions separate according to differences in gas-phase ion mobilities. Upon exiting the drift tube, ions enter a quadrupole mass filt er where a specific mass-to-charge (m/z) ratio can be selected prior to col lisional activation in an octopole collision cell. Parent and fragment ions that exit the collision cell are analyzed using a reflectron geometry time -of-flight mass spectrometer. The overall configuration allows different sp ecies to be selected according to their mobilities and m/z ratios prior to collision-induced dissociation and final MS analysis. A key parameter in th ese studies is the pressure of the target gas in the collision cell. Above a critical pressure, the well-defined: mobility separation degrades. The ap proach is demonstrated by examining a mixture of tryptic digest peptides of ubiquitin.