POST-SOURCE DECAY AND DELAYED EXTRACTION IN MATRIX-ASSISTED LASER DESORPTION IONIZATION/REFLECTRON TIME-OF-FLIGHT MASS-SPECTROMETRY - ARE THERE TRADE-OFFS/

By the incorporation of delayed extraction (DE) into matrix-assisted l aser desorption/ionization time-of-flight mass spectrometry a dramatic improvement of performance with respect to sensitivity, mass resoluti on and mass accuracy of precursor ions up to similar to 10 kDa has bee n achieved. Since DE reduces collisional in-source activation to a lar ge extent, the rate of subsequent metastable decay is considerably red uced, Results are presented which demonstrate that under DE the loss o f total post-source decay (PSD) fragment ion yield can be as large as one order of magnitude bur that, in terms of sensitivity, part of this loss is balanced by a better S/N ratio which results from a significa ntly improved mass resolution of the PSD fragment ions (M/Delta M up t o 1800 compared with M/Delta M=200-500 under prompt extraction). While this compensatory effect is true for the middle to high mass range of PSD fragment ions, it gradually vanishes towards the low mass end of the PSD mass scale where, in the case of linear peptides some importan t information (immonium ions) is lost. It appears, however, that in th e majority of practical PSD work, DE improves the qualty of the PSD sp ectra and that high energy collisional post-source activation can comp ensate for the occasional loss of analytical information.