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Freneil B. Jariwala John A. Hibbs Carl S. Weisbecker John Ressler Rahul L. Khade Yong Zhang Athula B. Attygalle 《Journal of the American Society for Mass Spectrometry》2014,25(9):1670-1673
We describe a diagnostic ion that enables rapid semiquantitative evaluation of the degree of oxygen contamination in the collision gases used in tandem mass spectrometers. Upon collision-induced dissociation (CID), the m/z 359 positive ion generated from the analgesic etoricoxib undergoes a facile loss of a methyl sulfone radical [?SO2(CH3); 79-Da] to produce a distonic radical cation of m/z 280. The product-ion spectrum of this m/z 280 ion, recorded under low-energy activation on tandem-in-space QqQ or QqTof mass spectrometers using nitrogen from a generator as the collision gas, or tandem-in-time ion-trap (LCQ, LTQ) mass spectrometers using purified helium as the buffer gas, showed two unexpected peaks at m/z 312 and 295. This enigmatic m/z 312 ion, which bears a mass-to-charge ratio higher than that of the precursor ion, represented an addition of molecular oxygen (O2) to the precursor ion. The exceptional affinity of the m/z 280 radical cation towards oxygen was deployed to develop a method to determine the oxygen content in collision gases. Figure
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Robert D. Hale Chang‐Ching Chan Carl S. Weisbecker Athula B. Attygalle 《Journal of mass spectrometry : JMS》2014,49(3):195-200
Upon collisional activation, gaseous metal adducts of lithium, sodium and potassium oxalate salts undergo an expulsion of CO2, followed by an ejection of CO to generate a product ion that retains all three metals atoms of the precursor. Spectra recorded even at very low collision energies (2 eV) showed peaks for a 44‐Da neutral fragment loss. Density functional theory calculations predicted that the ejection of CO2 requires less energy than an expulsion of a Na+ and that the [Na3CO2]+ product ion formed in this way bears a planar geometry. Furthermore, spectra of [Na3C2O4]+ and [39K3C2O4]+ recorded at higher collision energies showed additional peaks at m/z 90 and m/z 122 for the radical cations [Na2CO2]+? and [K2CO2]+?, respectively, which represented a loss of an M? from the precursor ions. Moreover, [Na3CO2]+, [39K3CO2]+ and [Li3CO2]+ ions also undergo a CO loss to form [M3O]+. Furthermore, product‐ion spectra for [Na3C2O4]+ and [39K3C2O4]+ recorded at low collision energies showed an unexpected peak at m/z 63 for [Na2OH]+ and m/z 95 for [39K2OH]+, respectively. An additional peak observed at m/z 65 for [Na218OH] + in the spectrum recorded for [Na3C2O4]+, after the addition of some H218O to the collision gas, confirmed that the [Na2OH] + ion is formed by an ion–molecule reaction with residual water in the collision cell. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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The standard enthalpy of formation, δfHo, of2 II CH has been determined at converged levels of ab initio electronic structure theory, including high order coupled cluster and full configuration interaction benchmarks. The atomic Gaussian basis sets employed include the (aug)-cc-p(C)VXZ family with X = 3, 4, 5 and 6. Extrapolations to the complete one-particle basis set and the full configuration interaction limits, where appropriate, have been performed to reduce remaining computational errors. Additional improvements in the enthalpy of formation of 2II CH were achieved by appending the valence-only treatment with core-valence correlation, relativistic effects including spin-orbit correlation, and the diagonal Born-Oppenheimer correction. The recommended values for δfHo 0 and δAf H o 298 of 2II CH are 592.48+0.47 ?0.56 kJ mol?1 and 595.93 +0.47 ?0.56 kJ mol?1, respectively. 相似文献
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New skutterudite compounds CaxCo4Sb12 (0<x?0.2) have been prepared by traditional metallurgical synthesis. The compounds have been characterized by X-ray powder diffraction (XRD), electron probe microanalysis (EPMA) and neutron powder diffraction. Rietveld refinement of the structures against neutron powder diffraction data (on Ca0.1Co4Sb12, , a=9.0429 Å, χ2=1.55; wRp=1.52) enabled the location of Ca in the voids of the skutterudite structure to be verified. The large displacement ellipsoid for Ca is consistent with “rattling” in the cage of the crystalline structure. XRD combined with EPMA analyses showed that the maximum occupancy of Ca atoms is about 0.2. 相似文献
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Isra Hassan Spencer Pinto Carl Weisbecker Athula B. Attygalle 《Journal of the American Society for Mass Spectrometry》2016,27(3):394-401
Carboxamides bearing an N–H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N–H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O?) preferentially form superoxide radical-anion (O2 -?) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2 -?) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2 -? adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O?) to generate the superoxide radical-anion (m/z 32) or the deprotonated amide [m/z (M – H)?], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N–H functionality undergo neither deprotonation nor adduct formation under HePI conditions. 相似文献
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Attygalle AB Bialecki JB Nishshanka U Weisbecker CS Ruzicka J 《Journal of mass spectrometry : JMS》2008,43(9):1224-1234
Collision-induced dissociation of anions derived from ortho-alkyloxybenzoic acids provides a facile way of producing gaseous enolate anions. The alkyloxyphenyl anion produced after an initial loss of CO(2) undergoes elimination of a benzene molecule by a double-hydrogen transfer mechanism, unique to the ortho isomer, to form an enolate anion. Deuterium labeling studies confirmed that the two hydrogen atoms transferred in the benzene loss originate from positions 1 and 2 of the alkyl chain. An initial transfer of a hydrogen atom from the C-1 position forms a phenyl anion and a carbonyl compound, both of which remain closely associated as an ion/neutral complex. The complex breaks either directly to give the phenyl anion by eliminating the neutral carbonyl compound, or to form an enolate anion by transferring a hydrogen atom from the C-2 position and eliminating a benzene molecule in the process. The pronounced primary kinetic isotope effect observed when a deuterium atom is transferred from the C-1 position, compared to the weak effect seen for the transfer from the C-2 position, indicates that the first transfer is the rate determining step. Quantum mechanical calculations showed that the neutral loss of benzene is a thermodynamically favorable process. Under the conditions used, only the spectra from ortho isomers showed peaks at m/z 77 for the phenyl anion and m/z 93 for the phenoxyl anion, in addition to that for the ortho-specific enolate anion. Under high collision energy, the ortho isomers also produce a peak at m/z 137 for an alkene loss. The spectra of meta and para compounds show a peak at m/z 92 for the distonic anion produced by the homolysis of the O--C bond. Moreover, a small peak at m/z 136 for a distonic anion originating from an alkyl radical loss allows the differentiation of para compounds from meta isomers. Copyright (c) 2008 John Wiley & Sons, Ltd. 相似文献
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