Analyzed Ion Kinetic Energy Spectrometry Research Articles

Gas-Phase Ion Chemistry and Organic Chemistry: The Story of a Hybrid Six-Sector Mass Spectrometer—The “AutoSpec 6F”

The AutoSpec 6F mass spectrometer is a large, floor standing instrument comprising a pair of commercial EBE geometry (AutoSpec) mass spectrometers coupled in series to provide an hybrid EBE-EBE configuration, (E and B being respectively electrostatic and magnetic sectors.) It was designed in close collaboration between Professor R. Flammang and VG Analytical in Manchester, UK. It was equipped with five collision cells and allowed the recording of high energy CID (collision induced dissociation), MIKES (mass analyzed ion kinetic energy spectrometry) and NRMS (neutralization re-ionization mass spectrometry) data as well as consecutive MSn analyses. The field-free regions between sectors allowed the study of unimolecular decomposition products from long-lived metastable ions. The mass spectrometer became even more versatile when an RF-only quadrupole collision cell was installed between the second and the third electric sector. This allowed the study of associative ion/molecule reactions in the low kinetic energy regime. Bimolecular chemical reactions were performed inside the quadrupole cell when a neutral reagent was introduced and the reaction products were analyzed by high energy CID in the downstream sectors. This paper tells the history and summarizes the capabilities of this versatile instrument.

ChemInform Abstract: Electron Impact Induced Synthesis of Benzo(2,1-b:3,4-b′)dithiophene.

The photochemical behaviour of cis and trans 1,2-bis(2-bromo-3-thienyl)ethene has been separately studied with respect to cyclization to benzo[2,1-b:3,4-b′]dithiophene (BDT). The gc/ms analysis of the mother liquors of the two isomers photoreaction shows the opposite direction of isomerization followed by production of intractable materials resulting by the radical breaking of one of the two C-Br bonds on the thiophene moiety. On the contrary, in EI mass spectrometry both the isomers give rise to fragment ions at m/z 190 studied and compared to BDT with the aid of mass analysed ion kinetic energy spectrometry and collisional spectroscopy.

Reactivity of anomeric 1alpha- and 1beta-pentofuranosyl azide derivatives in ammonia chemical ionization.

Electron impact (EI), fast atom bombardment (FAB) and ammonia chemical ionization [CI(NH3)] mass spectrometry were applied with the aim of differentiating between the anomeric 1alpha- and 1beta-azidopentofuranosyl derivatives. Calculated ammonium affinities [AA(M)] and proton affinities [PA(M)] show that beta-anomers have higher affinities for H+ and NH4+ ions than alpha-azides. Protonated molecules, obtained by CI(NH3) of azidofuranosyl derivatives, lose HN3 giving abundant furanosyl (S+) ions. Ammonia solvation of MH+ ions competes with the previous reaction producing the [SNHN2NH3]+ ion, a competitive product to the ammonium-attached [SN3NH4]+ ion. The fragmentation pathways of the stable and metastable [MNH4]+, MH+ ions, and several other important fragment ions, were determined using mass analyzed ion kinetic energy spectrometry (MIKES). The abundance of the [SN3NH4]+ and/or [SNHN2NH3]+ ions was found to correlate inversely with the exothermicity of ammonia solvation of the MH+ ion. The abundance of the fragment ions [SNHNH3]+, [SNH3]+ and SNH+ in some examples correlates with the exothermicity of the corresponding [MNH4]+ and MH+ parent ion formation. The fragment ions SNH3+ and SNHNH3+ can be formed, at least in part, in the ammonia solvation reaction of the S+ and SNH+ ions taking place within the high-pressure region of the CI ion source.

Mass spectrometric study of six cyclic esters

A series of cyclic esters, which are optically active as a consequence of their helical structures, were synthesized to investigate the relationships between their structures and their optical activities. This paper reports the electron impact fragmentation mechanisms of these six cyclic esters. Accurate mass measurements and mass analyzed ion kinetic energy spectrometry confirmed fragmentation patterns. The stability of the fragment ions has a great influence on the fragmentation pathways, but no correlation with the optical activity was found.

Fragmentation reactions of molecular ions and dications of indoleamines

The combination of techniques such as two-dimensional mass spectrometry and mass analysed ion kinetic energy spectrometry (with and without collision gas) in the study of gas-phase ion chemistry of indole, gramine, tryptamine and serotonine enabled us to estab lish the fragmentation pathways of their singly- and doubly-charged molecular ions generated by electron impact. The measurement of the kinetic energy released in the charge separation reactions of the molecular dications produced information on the intercharge distance on the transition state for the fragmentation, assuming that it arises entirely from the coulombic energy released. For the sin gly-charged molecular ions of indoleamines, loss of the neutral molecule CH 2=NR (R = H or CH3), by hydrogen transfer from the amino (or methyl) group to the indole nucleus, is the only fragmentation occurring in the third field-free region of the mass spectro meter. Upon collision of the molecular ion with He gas, a competing process of bond cleavage by loss of the radical ∞ CH2NH2 (or ∞ N(CH3)2 for gramine) is observed for tryptamine and serotonine. The doubly-charged ions dissociate by elimination of neutral molecules or radicals to generate doubly-charged fragment ions or by charge separation reactions. The intercharge distance, calculated from the kinetic energy released in the fragmentation, was, whenever possible, correlated with charge location in the ion.

Collision-induced dissociation of CS2+ to S2+ at kilovolt laboratory energies

Collision-induced dissociation (CID) of CS2 + molecular ions to S2 + ions at laboratory collision energies ranging from 1 to 6 keV energy has been studied by mass analyzed ion kinetic energy spectrometry (MIKES) utilizing a reversed geometry tandem mass spectrometer. The dissociation proceeds via four energetically distinct pathways which are strongly dependent upon the kinetic energy of the ion and on the nature of the collision gas. CID with argon neutrals is dominated at all energies by the lowest energy threshold reaction, which is endothermic by about 6 eV, whereas the energetics of the process differ and are strongly dependent on the ion kinetic energy when lighter collision gases (He, H2 and D2) are used for collisional activation. The most probable energy transfer from kinetic to internal modes is 11 ± 2 eV for these collision gases. A highly endothermic channel with kinetic energy loss of ~41 ± 4 eV opens up when the energy of the ions is reduced to 3 keV and less. At 1 keV ion energy, there is a small contribution to the total CID from a highly exothermic channel (kinetic energy release of 47 ± 5 eV) that is observed with all collision gases under low pressure conditions in the collision cell.

Synthesis and mass spectrometric investigations of some new coumarin derivatives

The electron ionisation induced decomposition pathways of a series of new coumarins, three psoralens, one allopsoralen and one angelicine have been studied in detail with the aid of mass analysed ion kinetic energy spectrometry. The examined compounds exhibit decomposition patterns well related to their structures and the characterisation of some isomer pairs has been obtained. Copyright © 1998 John Wiley & Sons, Ltd.

Mass spectrometry study on five‐substituted pyrroles and the related N‐methylene‐ 1,3,4‐thiodiazoles

Electron impact mass spectra of nine new substituted pyrroles are reported. Apart from compounds 1a and 1b, the other seven compounds produce R1--Ph--C≡O+ ions as base peaks. Except for compounds 2a–c, each compound may produce [M−EtOH]∔, [M−OEt]+ and other fragment ions. The proposed fragmentation mechanisms of the six new compounds giving M∔ ions have been supported by mass analysed ion kinetic energy spectrometry and accurate mass data. No molecular ion peaks of compounds 2a–c are observed under electron impact conditions. However, very intense protonated molecule peaks of compounds 2a–c were observed under fast atom bombardment conditions together with [M+H − EtOH]+ ions. By D-exchange experiments, it was verified that the proton is localized on the N atom between the carbonyl and thiocarbonyl groups during the formation of protonated molecules. © 1998 John Wiley & Sons, Ltd.

Mass spectrometric study on methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates

The mechanisms of mass spectrometric fragmentation of eight new compounds, including methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates (Group I, R = substituent) and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates (Group II, R = substituent), were studied using mass analyzed ion kinetic energy spectrometry. The chemical compositions of these compounds and some of their important fragment ions were verified by high-resolution MS data. There were two types of H-rearrangement as regards the route of fission. In one type, the γ-H migration was influenced by both the electron effect and the steric hindrance of substituents, whereas on the other α-H migration losing methanol was due to the α-position active hydrogen located between two carbonyls, and this was verified by the method of deuterium labelling. © 1997 John Wiley & Sons, Ltd.

Metastable and Collision-activated Decomposition of Protonated Molecules of Isomeric N7- and N9-Substituted Purines in the Gas Phase

The structures and reactivities of protonated metastable and collision-activated molecules of isomeric N7- and N9-substituted purines were investigated using fast atom/ion bombardment ionization and mass analysed ion kinetic energy spectrometry methods. Calculated proton affinities (PAs) of isomeric purine derivatives and the intensities of the observed metastable-ion peaks revealed a direct correlation of PA with the reactivity of protonated molecules. The reactivity of the N9-substituted purines possessing N3-site specific proton affinities, i.e. N3–H+, relates to the strength of hydrogen bonding of N3–H+ to oxygen atoms(s) of the N9-substituent, e.g. CH2—O—CH2CH2—O—C(CH3) = O or CH2—OCH2CH2—O—H. Various intramolecular (‘intra-ion’) hydrogen-bond(s) in the protonated molecules of isomeric purine derivates were revealed using proton affinities and metastable-ion peak intensities. © 1997 John Wiley & Sons, Ltd.

A study of protonated molecules of crown ethers containing two thiourea segments by collision‐induced dissociation mass analysed ion kinetic energy spectrometry

AbstractFast atom/ion bombardment mass spectrometry was used to investigate the structures of protonated molecules of macrocyclic nitrogen‐containing crown ethers with two polyoxyethylene chains linked by two thiourea groups. The collision‐induced dissociation (CID) of their MH+ ions, using the mass analysed ion kinetic energy (MIKE) spectrometry method reveals four clearly defined competitive fragmentations. The product‐ion intensities clearly show that, in the MH+ ions of asymmetric crown ethers, the proton is preferentially located in the region of the longer polyoxyethylene chain. The characteristics of CID MIKE spectra of isomeric crown ethers are discussed.

Rearrangement by intermediate ion/neutral complexes during the McLafferty fragmentation of unsaturated ketones

The fragmentation of 1-phenylhex-5-ene-1-one 1 was studied by mass analyzed ion kinetic energy spectrometry of its deuterium and ''carbon labelled derivatives as a further example of interactions within ion/neutral complexes, The analysis of the MIKE spectra demonstrate two important reaction channels of metastable molecular ions, The first one is a McLafferty rearrangement by elimination of a 1,3-butadiene molecule, The second energetically even more favoured fragmentation corresponds to the loss of an ethyl radical. The MIKE spectra of labelled molecular ions, especially that of the (13)carbon labelled compound, indicate a skeletal rearrangement specifically of the butenyl moiety of the alkyl side chain by interchanging the terminal carbon atoms C-6 and C-5 with the inner C atoms C-3 and C-4 prior to the loss of the ethyl radical, This specific skeletal rearrangement is explained by an internal return within an intermediate ion/neutral complex f, consisting of the acetophenone enol radical cation and the neutral butadiene, by addition of the enol radical cation to the remote double bond of the diene, The second reaction channel is the irreversible cyclization of an intermediate distonic ion c leading to the formation of an ionized ethyl-alpha-dihydronaphthol d. This ion is stabilized by loss of an ethyl radical resulting in protonated alpha-naphthol e.

Intermediate ion–neutral complexes formed during the gas‐phase protonolysis of p‐(tert‐butyl)‐substituted α,ω‐diphenylalkanes

AbstractLoss of isobutane is the exclusive fragmentation channel of long‐lived protonated tert‐butyl‐substituted α,ω‐diphenylalkanes with chain lengths n = 2–12. Methane chemical ionization/mass‐analysed ion kinetic energy spectrometry of the [M + H]+ ions and several deuterium‐labelled tert‐butyl‐substituted 1,2‐, 1,3‐ and 1,10‐diphenylalkanes revealed that the reaction involves with equal probability and maximum regioselectivity a hydride ion from both the adjacent and the remote benzylic methylene groups, irrespective of the length of the aliphatic chain. The isotope effect of the hydride abstraction step was found to be same in all cases, k[C4H10]/k[C4H9D] = 1.6 ± 0.1. A sterically restricted system, protonated 1‐benzyl‐4‐(tert‐butylbenzyl)benzene, shows the same behaviour. This implies, as a general phenomenon, the formation of intermediate ion–neutral complexes [C4H9+ Ar(CH2)n Ar] along with (or instead of) the corresponding π complexes [C4H9+ …︁ Ar(CH2)nAr] prior to isobutane elimination (Ar represents a phenyl or substituted‐phenyl group).

Fast‐atom bombardment/mass‐analysed ion kinetic energy spectrometry of inositol phosphates

AbstractThe application of fast‐atom bombardment mass Spectrometry and collisiorutlly induced dissociation with mass‐analysed ion kinetic energy (CID/MIKE) Spectrometry of representative inositol mono‐, bis‐ and trisphos‐phates is described. Based on their CID/MIKE spectra, inositol polyphosphates containing vicinal phosphate groups could be distinguished from isomers in which adjacent phosphate groups were absent. The potential value of this procedure in studies of the biochemistry of intracellular second messengers is discussed.

Analysis of tetrabenzyl N‐giucosidic, N‐mannosidic and N‐galactosidic Isomers using fast atom bombardment/mass‐analysed ion kinetic energy spectrometry

AbstractA series of new synthetic tetrabenzyl N‐glucosidic, N‐mannosidic and N‐galactosidic isomers were investigated by fast atom bombardment (FAB)/mass‐analysed ion kinetic energy (MIKE) spectrometry. The [M + H]+ ions were obtained with high abundance in the FAB spectra when using 3‐nitrobenzyl alcohol as the matrix. The FAB/MIKE spectra provide characteristic daughter ions fragmented from selected molecular parent ions, allowing these isomers to be differentiated. In addition, an interesting rearrangement was found from the MIKE spectra, indicating that the benzyl (Bzl) group on the sugar ring is rearranged on to the N atom of the base (R) group to form [R + Bzl + H]+ and [R+ 2Bzl]+ ions.

A Study of Ion Kinetic Energy Spectrometry of Ferrocene Doubly Charged Ions in Gas Phase

The unimolecular charge separation reactions of the doubly charged ions FeC10H102+, FeC10H theta 2+, FeC10H82+ produced in the ion source by electron impact from ferrocene have been studied using Mass analyzed Ion Kinetic Energy Spectrometry (MIKES) technique. From the values of the kinetic energy releases (T), the intercharge distances (R) of the exploding doubly charged ions in their transition structures have been estimated and some structural informations about the transition states can be obtained. The collision induced reactions of the FeC10H102+ ion with Ar have been studied using MIKES, we postulate a new type of continuing reaction which may be collisional charge separation induced dissociation.

Electron impact induced synthesis of benzo[2,1‐b:3,4‐b′]dithiophene

AbstractThe photochemical behaviour of cis and trans 1,2‐bis(2‐bromo‐3‐thienyl)ethene has been separately studied with respect to cyclization to benzo[2,1‐b:3,4‐b′]dithiophene (BDT). The gc/ms analysis of the mother liquors of the two isomers photoreaction shows the opposite direction of isomerization followed by production of intractable materials resulting by the radical breaking of one of the two C‐Br bonds on the thiophene moiety. On the contrary, in EI mass spectrometry both the isomers give rise to fragment ions at m/z 190 studied and compared to BDT with the aid of mass analysed ion kinetic energy spectrometry and collisional spectroscopy.

Quantitation by fast‐atom bombardment/mass‐analysed ion kinetic energy spectrometry: Kinetic analysis of cyclic nucleotide phosphodiesterase activity

Quantitation of cyclic nucleotide phosphodiesterase activity by means of fast-atom bombardment (FAB) mass spectrometry with mass-analysed ion kinetic energy (MIKE) spectrum scanning is described. Characteristic peaks of the substrate, cyclic AMP, and product, AMP, were identified in positive-ion FAB mass spectra and MIKE scans of the protonated molecules. By spiking enzyme incubates with known quantities of cyclic AMP and AMP and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the concentrations of cyclic AMP and AMP in solution at the end of a series of enzyme incubations have been estimated. From the data obtained the Km and Vmax of the enzymes were calculated as 181 microM and 28.6 nmol/min respectively, showing excellent agreement with values of the Michaelis constant, Km = 205 microM and the maximum velocity Vmax = 33.2 nmol/min obtained by radioactive assay.

On the structure of some electron impact induced fragmentation products of Si(C 6H 5) 4, Ge(C 6H 5) 4 and Sn(C 6H 5) 4

The electron impact mass spectrometric behaviour of tetraphenyl derivatives of Si, Ge and Sn is discussed on the basis of results of exact mass measurements, linked scans, mass analysed ion kinetic energy spectrometry, and collisional experiments. The possible structures of fragment ions are discussed, and the relevance of the findings to solution chemistry is considered.

Electron impact mass spectrometry of 3‐hydroxy‐3,4,5,6‐tetrahydro‐2H‐[1]benzoxocines. A comparison with the behaviour of isomeric 2‐hydroxymethyl‐2,3,4,5‐tetrahydro‐[1]‐benzoxepines and 1,2‐epoxy‐5‐(2‐hydroxyphenyl)pentane

AbstractThe mass spectrometric behavior of 3‐methyl‐3‐hydroxybenzoxocines has been studied in detail by means of linked scans and mass analyzed ion kinetic energy spectrometry. The structure of the molecular ion and the fragmentation processes are strictly related to the structure of the neutral moieties.The possible isomerization of 3‐hydroxy‐10‐methoxy‐3‐methyl‐3,4,5,6‐tetrahydro‐2H‐[1]benzoxocine to 2‐methyl‐2‐[3‐(3′‐methoxy‐2′‐hydroxy)phenyl]pentyloxirane and to 2‐hydroxymethyl‐9‐methoxy‐2‐methyl‐2,3,4,5‐tetrahydro[1]benzoxepine is investigated.