Maurice M. Bursey

Eluent pH and thermospray mass spectra: does the charge on the ion in solution influence the mass spectrum?

Abstract The thermospray (with buffer, without filament) mass spectra of the nine compounds studied in this paper exhibit little change as the charge on the predominant analyte ion in solution changes. In addition, the reagent ions observed in positive and negative ion thermospray are seen to decrease as the sample elutes. These observations indicate that, under the conditions employed in this study, gas-phase ionization predominates. This conclusion is further supported by the difference between the thermospray and fast atom bombardment mass spectra of those compounds that exhibit poor sensitivity in thermospray. The poor sensitivity of certain solutes in thermospray can be explained in terms of the inability of the ammonium ion to protonate those solutes in positive ion thermospray. In negative ion thermospray, those solutes with higher gas-phase proton affinities than the acetate ion will not be detected.

Unimolecular and collision induced decompositions of gas-phase group IV a enium ions (CH3)3M+

Abstract The fragmentation characteristics of the trimethyl-Group IV cations have been studied using mass analyzed ion kinetic energy (MIKE), V 1 2 / E (linked) metastable and consecutive reaction monitoring techniques. Both unimolecular (low energy) and collision induced (high energy) decompositions were studied. These methods give information on the ion of interest without interfering contributions from the precursor ion of the trimethyl cation. The results have been interpreted in terms of the decreasing metal—carbon bond strength and the increasing preference for the +2 oxidation state going down Group IV from carbon to lead.

Conversion of kinetic energy to internal energy in the 2-pentanone molecular ion at threshold in low-energy collisions with helium target atoms

Abstract Values of the threshold kinetic energy for formation of m/z 58 and m/z 43 from 2-pentanone molecular ion after collisional activation (CA) with He were studied in a hybrid tandem quadrupole system. These values indicate that the fraction of kinetic energy converted to internal energy and available for fragmentation is 0.14–0.25. Onset of conversion to internal energy through an electronically excited state was observed at 2.0 eV. Uses of He and heavier gases as collision gases in low-energy CA are projected to differ, He being used to screen classes of compounds and heavier gases to provide more complete structural information for ions.

Survey of reaction types in low-energy colliosional activation of protonated methyl alkyl ketones

Abstract In contrast to high-energy collisions, where simple cleavages are commoner, rearrangements typically account for 96–100% of products in low-energy collisions of the [M + 1] + ions of aliphatic methyl ketones. Rules for predicting low-energy helium collsional-activated decomposition (CAD) spectra of the ketones are based on proton affinities of fragments formed by simple rearrangements. The commonest reaction is equivalent to the energetically improbable four-center 1,3-H or 1,3-R shift; other rearrangements equivalent to processes with five-, six-, or seven-center activated complexes are less important. In larger ions, loss of water followed by loss of alkene dominates. O -Protonated enol forms either lose water to give a carbonium ion that rearranges to forms capable of losing olefin fragments, or rearranges to an intermediate in the formation of acetyl ion and an alkane. O -Protonated keto forms rearrange to alkanes and protonated smaller carbonyl compounds. The ion kinetic energies necessary to produce several intense daughter ions at threshold establish the order of sequential fragmentations. When helium is the collisional gas and the ion energy is 30 eV in the laboratory frame (the maximum value studies), the ion energy is only 0.8–1.9 eV in the center-of-mass frame depending on its size. Only a fraction of this kinetic energy is converted to internal energy, so that onsets of reaction channels differing by several tenths of an electron-volt are easily studied. Some isomers of methyl ketones can be easily distinguished by He-CAD spectra of their [M + 1] + ions.

Formation of small cluster ions from alkali halides in SIMS

Abstract An experimental investigation of M2X+ cluster ion formation by alkali halides in secondary ion mass spectrometry is presented as evidence of a gas phase cluster ion formation mechanism. Experimental M2X+ ion yields are compared with calculated heats of formation for M2X+ ions formed from binary mixtures of alkali halides, MX (M = Li, Na; X = F, Cl). The cluster ion intensity order was found to be Li2F+ > Li2Cl+ > Na2F+ > Na2Cl+, consistent with gas phase mechanism predictions. This ordering may be affected, however, by experimental artifacts such as mass discrimination by the quadrupole mass spectrometer, and variations in composition caused by sample preparation or preferential sputtering. Steps are taken to limit quadrupole mass discrimination, and X-ray photoelectron spectroscopy (XPS) is used to examine surface stoichiometry changes induced by sputtering. The XPS study suggests that, although preferential sputtering did occur, it did not influence the relative ordering of cluster ion intensities.

Electrochemically deposited cobalt emitters for field ionization and field desorption mass spectrometry

Optimum conditions for the growth of cobalt dendrites upon tungsten wire for use as field desorption and especially field ionization emitters are described. The new emitters and superior to nickel emitters for field ionization and are most simple to manufacture than carbon emitters; their growth may also be localized at will along the wire.

σ-π conjugation in group IVA compounds of indene and indane

Abstract A series of indanyl and indenyl derivaties of silicon and tin has been prepared and the molecular ionization potentials determined by electron impact mass spectrometry. Substitution of the hydrogen at C(1) by an organosilicon group results in a decrease of the ionization potential by ∼0.6–0.8 eV, while extension of the π-system into the five-membered ring via the double bond produces a further decrease of the ionization potential by ∼0.2–0.3 eV. The results are consistent with the postulate of a σ-gp hyperconjugative interaction between the β metal-carbon bond and the aromatic π-system.

Effects of metal-ligand charge transfer on the mass spectra of bis(N,N-diethyldithiocarbamato) complexes. An application of the shannon-swan rule

Abstract The mass spectra fragmentation patterns of bis(N,N,-diethyldithiocarbamato) copper(II) and zinc(II) follow the Shannon-Swan rule, apparently because of the ability of copper(II). It is also observed that the short out-of-plane bonds between the two halves of the zinc dimer are strong enough for ions containing two zinc atoms to be observed under the severe experimental conditions employed, while the out-of-plane bonds in the copper dimer are too weak for species containing two copper atoms to be observed.

Distinguishing 1,2-cyclopentanediol isomers via gas-phase reactions with trimethyl-group 14 cations

Abstract Reactions with trimethyl-group 14 (CH 3 ) 3 X + ions (X = C, Si, Gen, Sn) are used to distinguish between cis - and trans -1,2-cyclopentanediol isomers in a triple quadrupole mass spectrometer. At a kinetic energy of 1.2 eV (center of mass), there are substantial differences in the decomposition behavior of the [ M + (CH 3 ) 3 X] + adducts, particularly for trimethylsilyl and trimethylgermyl ions. The cis -1,2-cyclopentanediol isomer favors decomposition of [ M + (CH 3 ) 3 X] + to produce a hydrated trimethyl-group 14 ion [(CH 3 ) 3 XOH 2 ] + . For the trans -diol, formation of [(CH 3 ) 3 XOH 2 ] + apparently is an endothermic process requiring additional energy input. At the ion kinetic energy employed, trans -1,2-cyclopentanediol exhibits greater adduct ion stabilities. The trimethylgermyl reactant was found to be more sensitive and stereochemically selective than the other group 14 cations. The t-butyl ion in contrast provided the least effective stereochemical probe.

Reactions of carbonyl compounds and group 1b metals in a plasma in the wake of a spark

The reaction of the model system of C3H6 and Cu to produce cationized species Cn,Hm,Cu+ in the spark source mass spectrometer proceeds through neutral organic species and Cu+. On this basis reactions of Cu+, Ag+ and Au+ with neutral methyl, ethyl and propyl ethanoate, butanone, butanal, 2,4-pentanedione, ethanoic acid and ethanoic anhydride are compared with reactions of similar compounds with laser-generated Cu+ in an ion cyclotron resonance spectrometer. In the wake of the spark more fragmentation of the cationized organic species is observed. The simple cationized molecule is not observed if the metal ion has low-lying excited states.