THE FOURIER TRANSFORM MASS SPECTROMETER AS A GAS PHASE CHEMICAL LABORATORY: INSTRUMENTAL DEVELOPMENTS AND CHEMICAL STUDIES
Abstract
New aspects of Fourier transform mass spectrometry (FTMS) are discussed and demonstrated in the studies of laser desorbed gas phase metal ion chemistry with alkanes and organosulfur compounds. In an extension of laser desorption studies, multiphoton ionization in FTMS has been showed to be a straightforward and efficient ionization method. FTMS is very compatible with laser ionization methods and permits high resolution detection and various trapped ion studies. A major limitation in FTMS performance is interference by the neutral gas pressure in the analyzer cell. Pulsed valve techniques have been developed which dramatically increase the back-end mass resolution (> 30,000 at M/z 91) available in collision-induced dissociation (CID) experiments. Also, since the pulsed valve can introduce pressures well above the maximum static pressure limits in FTMS, previously unaccessible high pressure processes can be studied. The gas phase chemistry of V('+) and VO('+) with alkanes has been studied. V('+) reacts mainly by inducing multiple dehydrogenations, but some evidence for C-C bond cleavage is observed for branched alkanes. VO('+) reactively is similar but slightly reduced compared to the bare metal ion and no oxygen loss products are observed. The gas phase chemistry of several transition metal ions has been investigated with mercaptans and organosulfides. Fe('+), Co('+), and Ni('+) react to form mainly products corresponding to M('+)-alkene and M('+)-RSH ions. Rh('+) undergoes similar reactions and, in addition, forms dehydrogenation products. Ti('+) and V('+) form major amounts of MS('+) and also MS-alkene('+) products. Metal polysulfide ions are formed for all these metal ions by sequential sulfur abstractions from ethylene sulfide. Observed reactivity gives limits on the homolytic metal ion-S bond energies: D(M('+)-S) > 102 kcal/mole for Ti('+) and V('+); D(Rh('+)-S) > 59 kcal/mole; and 59 kcal/mole < D(M('+)-S) < 74 kcal/mole for Fe('+), Co('+), and Ni('+). Using pulsed valve techniques, MS('+) ions have been formed and reacted with alkanes free from reagent gas interference. Gas phase metal hydride ions have been synthesized in a multistep process and their chemistry with alkanes is reported. These experiments demonstrate how instrumental developments have increased the chemical sophistication available in FTMS studies.
Degree
Ph.D.
Subject Area
Analytical chemistry
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