Field desorption mass spectrometry with high temperature activated emitters

Abstract

The use of emitters which have been activated at high temperature in Field Ionization and Field Desorption mass spectrometry offers some important advantages over the usual emitter type activated at room-temperature. Higher thermal stability of the microneedles is achieved and the emitters are extremely resistant to chemical attack. It becomes possible to induce a thermal fragmentation of solid compounds adsorbed on the emitter surface between room-temperature and approximately 2000°C. The field anodes may be re-used many times without loss of quality. The problem of mass references is solved in Field Ionization/Field Desorption-Mass Spectrometry when high temperature emitters are used. The Field Ionization mass spectra of perfluorokerosene (PFK) and perfluorotributylamine display peaks in the mass range between m/e 50 to 800, with a resolution of up to 30000 (10% valley definition). A short description of a rapid and easy activation to produce high temperature microneedles is given.The following abbreviations are used throughout this paper:-HT RT BAT HR MS EI FI CI FD High Temperature Room-Temperature Best Anode Temperature High Resolution Mass Spectrometry/Spectrum/Spectra Electron Impact Field Ionization Chemical Ionization Field Desorption I N T R O D U C T I O NSINCE the introduction of FD-MS of organic molecules" by Beckeyl there has been rapid and continuous development in the technique for the preparation of field anodes. This is because the emitter quality is of essential importance for the ion-yield and the achievement of detectable ion currents. Whilst the single-focusing instruments showed remarkable results in amino-acid chemistry and peptide ~e q u e n c i n g ,~.~ only one high resolution FD-MS study has been published to date.4 As the structure of the high temperature activated emitter is not changed at temperatures up to 2000°C5 and is not destroyed at higher field strengths (for example a total potential difference of 16 kV across a gap (d) of 0.5 mm field anode to cathode), this emitter type seems to be a basic requirement for a more widespread application A major aim in our research programme has been the utilisation of FD-MS for problems in cancer research. Specifically, the reaction between anti-tumour alkylating zgents or their metabolites and deoxyribonucleic acid (DNA) may be a principal cause of the cytostatic action of these compounds.0 In view of the importance of DNA in this field, the high resolution FD-MS of DNA components are being investigated. The * The term FD-MS denotes the technique where the field anode is dipped into a solution of a sample to be analysed. 885of FD-MS.

Field Desorption Mass Spectra of Gastrine Peptides and Glutathione Derivatives

“…combination ion source. Activated 10 jum tungsten field ion emitters were uniformly prepared by a high temperature activation procedure developed by Beckey and Schulten [9] and were used once for each peptide. The peptides were dissolved in DMSO at concentrations of 50-100 jug/20 ju\ and loaded on the emitter by the dipping technique [8].…”

“…mass spectrometry has become an established tool for the molecular weight determination of large, polar and/or thermally unstable molecules [8,9]. Abundant molecular ions were obtained in f.d.…”

Field desorption mass spectrometry of sodium carboxylates. Intermolecular exchange of hydrogens and alkyl groups as shown by labelling

“…Although sodium acetate has become the prototypical organic salt for field desorption mass spectrometry (FDMS) studies (1)(2)(3)(4)(5), a number of questions about its behavior remain unanswered. The first reported spectrum (1) showed rnlz 23 (Na+) as base peak at 25, 30, and 32 mA, with no other ions at the lowest anode temperature, some ions of structural significance at 30mA (chiefly rnlz 105), and decomposition products at 32mA.…”

“…The first reported spectrum (1) showed rnlz 23 (Na+) as base peak at 25, 30, and 32 mA, with no other ions at the lowest anode temperature, some ions of structural significance at 30mA (chiefly rnlz 105), and decomposition products at 32mA. In a later description of this work it was pointed out (4) that mlz 105 is only the first member of a series of cluster ions [NaxOAcx-,] where x = 2 and that ions are found corresponding to higher values ofx to the limit of the mass scale.…”

Fragmentation of the α-Amino Acid Methionine in Field Desorption Mass Spectrometry

“…In addition to intense molecular ions or cationized molecules [2][3][4][5][6], thermally/field induced fragmentation is often observed which can be useful for structural studies. However, an essential prerequisite for the interpretation of these spectra is the basic understanding of the characteristic features for fragmentation in FD-MS.…”