APPLICATION OF THE POST-SOURCE PULSE-FOCUSING TECHNIQUE IN MATRIX-ASSISTED-LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY - OPTIMIZATION OF THE EXPERIMENTAL PARAMETERS AND THEIR INFLUENCE ON THE CAPABILITY OF THE METHOD/

This paper describes experiments demonstrating the performance of a li near time-of-flight mass spectrometer equipped with the post-source pu lse-focusing (PSPF) technique. The influence of various experimental p arameters like the shape of the PSPF pulse on the performance of the i nstrument is discussed. The application of an ion lens in the accelera tion region allows the focusing of high mass ions on the detector with a high yield. The observed mass resolution for matrix-assisted laser desorption/ionization (MALDI) generated ions is about 7000 (FWHM) and the mass accuracy using external standards for calibration is about 0. 05% or better, in this work demonstrated for molecules with a mass up to 5700 Da, The percentage of the complete mass spectrum which can be detected with increased resolution and accuracy depends on the geometr y of a particular setup. In order to cover a broad mass range several parameter sets have to be applied one after the other. Instead of the commonly employed microchannel plates, microsphere plates were used fo r detection of the ions in these experiments in order to test their ap plicability in combination with MALDI. (C) 1998 John Wiley & Sons, Ltd .