Delayed extraction

Abstract: A new type of ion gun is described which greatly improves the resolution of a nonmagnetic time‐of‐flight mass spectrometer. The focusing action of this gun is discussed and analyzed mathematically. The validity of the analysis and the practicability of the gun are demonstrated by the spectra obtained. The spectrometer is capable of measuring the relative abundance of adjacent masses well beyond 100 amu.

Abstract: We describe the impact of advances in mass measurement accuracy, ±10 ppm (internally calibrated), on protein identification experiments. This capability was brought about by delayed extraction techniques used in conjunction with matrix-assisted laser desorption ionization (MALDI) on a reflectron time-of-flight (TOF) mass spectrometer. This work explores the advantage of using accurate mass measurement (and thus constraint on the possible elemental composition of components in a protein digest) in strategies for searching protein, gene, and EST databases that employ (a) mass values alone, (b) fragment-ion tagging derived from MS/MS spectra, and (c) de novo interpretation of MS/MS spectra. Significant improvement in the discriminating power of database searches has been found using only molecular weight values (i.e., measured mass) of >10 peptide masses. When MALDI-TOF instruments are able to achieve the ±0.5−5 ppm mass accuracy necessary to distinguish peptide elemental compositions, it is possible to matc...

Abstract: A linear time-of-flight mass spectrometer has been modified to incorporate pulsed ion extraction of matrix-assisted laser desorption/ionization (MALDI) generated ions. A unique aspect of the experiments presented is the combination of pulsed extraction with very high source potentials (up to 25 kV) which allows improved mass resolution while maintaining excellent sensitivity for the large m/z ions generated by the MALDI technique. Mass resolution in excess of 1000 (fwhm) is demonstrated for cytochrome c (12 361.1 Da) with the pulsed ion extraction linear time-of-flight mass spectrometer described. The influence on obtainable mass resolution of experimental variables such as delay time between laser ionization and ion extraction, amplitude of the pulsed voltage employed, and the source bias voltage are presented. It is shown that, for any given source potential, the optimum pulsed extraction voltage is a linear function of the mass of the analyte. This is consistent with the observation that the initial ion velocity distribution for MALDI-generated ions is independent of mass.