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 spectrometer (IT/RETOFMS) has been used to enhance resolution in the ultraviolet matrix‐assisted laser desorption/ionization (MALDI) of peptides. The MALDI of peptides is performed directly inside an ion‐trap storage device using 266 nm laser radiation from a 2,5‐dihydroxybenzoic acid matrix. 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 nearly 6200 is obtained‐for Substance P using a 90 ms storage time. A resolution of 3000–6000 is consistently obtained for peptides up to 2100 u used in this study. The individual ion peaks from the isotopic distribution are easily resolved under these conditions. In addition, the ion trap is found to be useful as an ion‐storage device for enhancing the signal where multiple laser desorption pulses can be stored per cycle in the trap before ejection into the RETOF. Also, using the relatively high resolving power of the IT/RETOF instrument, excellent mass accuracy can be obtained using the matrix background and bradykinin as internal standards.