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.

Abstract

This paper describes experiments demonstrating the performance of a linear time-of-flight mass spectrometer equipped with the post-source pulse-focusing (PSPF) technique. The influence of various experimental parameters like the shape of the PSPF pulse on the performance of the instrument is discussed. The application of an ion lens in the acceleration 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 geometry 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 for detection of the ions in these experiments in order to test their applicability in combination with MALDI.