MALDI induced saturation effects in chevron microchannel plate detectors

Pulsing the gain from a low level to a high level is an effective way to reduce or eliminate saturation of a chevron microchannel plate detector struck by large numbers of low molecular weight ions, such as the matrix ions generated in matrix-assisted laser desorption-ionization events. In this study, we used a switching circuit to vary the initial voltage across the first microchannel plate from 37 to 100% of its final, full-gain voltage. This has enabled us to examine microchannel plate saturation over a broader range of gain than any previously reported. Experiments with a proteolytic digest of a protein clearly demonstrate that apart from the matrix ions, the ions from a lower mass molecule in a mixture can make it more difficult or even impossible to detect signals from larger molecules originating from the same mixture. Composite spectra, which might provide a more complete accounting of the compounds present in a mixture, can be easily produced by varying the switching delay in steps during the course of acquisition, (C) 1997 Elsevier Science B.V.