ENHANCEMENT OF RESOLUTION IN MATRIX-ASSISTED LASER-DESORPTION USING AN ION-TRAP STORAGE REFLECTRON TIME-OF-FLIGHT MASS-SPECTROMETER

A quadrupole ion-trap storage/reflectron time-of-flight mass spectrome ter (IT/RETOFMS) has been used to enhance resolution in the ultraviole t matrix-assisted laser desorption/ionization (MALDI) of peptides. The MALDI of peptides is performed directly inside an ion-trap storage de vice using 266 nm laser radiation from a 2,5-dihydroxybenzoic acid mat rix. Helium buffer gas is used to collisionally cool the hot desorbed ions and to rapidly relax the ions to the center of the ion trap. The result is that upon ejection into the TOF device, a resolution of near ly 6200 is obtained for Substance P using a 90 ms storage time. A reso lution of 3000-6000 is consistently obtained for peptides up to 2100 u used in this study. The individual ion peaks from the isotopic distri bution are easily resolved under these conditions. In addition, the io n trap is found to be useful as an ion-storage device for enhancing th e signal where multiple laser desorption pulses can be stored per cycl e in the trap before ejection into the RETOF. Also, using the relative ly high resolving power of the IT/RETOF instrument, excellent mass acc uracy can be obtained using the matrix background and bradykinin as in ternal standards.