Mass-analyzed Ion Kinetic Energy Research Articles

Mass-analysed ion kinetic energy and collisionally induced dissociation mass spectra of clusters of acetylated xylo-oligosaecharides with protonated ammonia and methylannine

Per-O-acetylated methyl glycosides of D-xylan-type di- and trisaccharides were studied by mass-analysed ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass Spectrometry using protonated ammonia and methylamine, respectively, as reaction gases in chemical ionization (CI). The oligosaccharides form abundant cluster ions, [M + NH 4] + or [M + CH 3NH 3] +, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH 3) or CI (CH 3NH 2) spectra in combination with the MIKE or CID spectra allow the molecular masses, the masses of monosaccharide units and the branching point in oligosaccharides to be established. In the case of disaccharides, it is possible to distinguish the (1 2) linkage from the other types of linkages.

Electron impact and fast atom bombardment mass spectrometry in the characterization of some new macrocycles containing a 1,3,5-triazine moiety

The mass spectrometric behaviour of four new macrocyclic compounds, all containing the 1,3,5-triazine moiety, was studied with the aid of different ionization methods and mass-analysed ion kinetic energy spectrometry. Extensive fragmentation of the oligoethylene glycol side-chains is observed, with the usual loss of C 2 H 4 O units. The favoured cleavage of the ethereal bond nearest to the etherocyclic ring gives rise to both complementary ions

Fast atom bombardment in the structural identification of intermediates in the hydrolytic degradation of polyphosphazenes

Fast atom bombardment mass Spectrometry was employed in a study related to the hydrolytic degradation of alanine ethyl ester- and imidazole-substituted polyphosphazenes, to be used as matrices for drug release. Some intermediates were identified and their structural assignment was accomplished by means of mass-analysed ion kinetic energy data. All the detected species show the same phosphazene skeleton, consisting of a P4N3 chain, with an increasing number of alanine ethyl ester substituents, and no evidence was found for the presence of imidazole bound to the polymer backbone.

Ion/molecule reactions of tert-butyl cation with tertiary alcohols

The tert-butyl cation ( tBu +) is widely used as a chemical ionization reagent ion, for which it is often assumed that simple proton transfer to neutral substrates is the dominant reaction. Mass-analyzed ion kinetic energy (MIKE) spectrometry and the collisionally activated decomposition (CAD) of ions corresponding to the adducts R′O(H)R + formed from mixtures of ROH and R′OH (R = tBu, R′ = tBu or 1-methylcyclopentyl, and their deuterated analogues) show a much more complicated pattern of reactivity, which is mirrored in the bimolecular reactions of tBu + with R′OH in the Fourier transform ion cyclotron resonance (FT-ICR) technique. Production of R′ + in the CAD and FT-ICR experiments is accompanied by isotopic exchange between the alkyl groups, which implicates ion-neutral complexes as accessible intermediates in addition to the covalent adduct ions. A unified pathway for MIKE spectrometry, CAD, and FT-ICR regimes is presented, involving terbody complexes of the form [cation water alkene] as well as two-body complexes of the form [cation alcohol].

Origin of the tailing signal on the low-energy side of the main beam in mass-analyzed ion kinetic energy spectra

The tailing signal on the low-energy side of the precursor ion signal observed during fast atom bombardment (FAB) mass-analyzed ion kinetic energy spectrometric (MIKES) analyses is due largely to ions of higher m/z value than the chosen precursor. The majority of these ions are independent, unfragmented species that emerge from the ion source with less than the full amount of kinetic energy predicted by the source potential. The tailing precursor ion signal observed under helium collision-activated decomposition conditions is too short to account for the protracted MIKES tail (as judged from mass-to-charge ratio-deconvoluted MIKES analyses performed on a BEqQ hybrid instrument), and a tailing precursor signal is not observed under unimolecular decomposition conditions. Measurements of the mass-to-charge ratios of the ionic species comprising the MIKES tail demonstrated that ions higher in mass-to-charge ratio than the chosen precursor are present throughout the tail, with the mass-to-charge ratio increasing as kinetic energy decreases. These ions possess the same momentum as the chosen precursor, and thus were formed prior to the magnetic field. The existence of intact, source-formed [M + M]+ ions with reduced kinetic energy was demonstrated through several types of tandem mass spectrometric experiments. These [M + H]+ ions with reduced kinetic energy do not appear to have undergone collisional deceleration, because they do not possess increased internal energy (as judged by observation of their fragmentation patterns). The kinetic energy profiles of unfragmented FAB-desorbed ions were determined and found to exhibit a tailing character similar in appearance to that of the MIKES tail. The population of ions emerging from the source under FAB conditions thus incorporates the characteristics necessary to account for the MIKES tail, namely, the presence of ions of a mass-to-charge ratio higher than the chosen precursor (due to matrix and other background ions), which possess reduced kinetic energy such that their momentum is identical to that of the selected precursor. These ions may arise via desolvation and declustering processes in the acceleration region of the ion source, or via FAB or chemical ionization processes in regions removed from the FAB target.

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.

Fast atom bombardment mass spectrometry of mycobacterial glycopeptidolipid antigens: structural characterization by charge remote fragmentation

Mycobacteria contain species- and type-specific antigens. Among them, glycopeptidolipids are present in medically relevant organisms belonging to Mycobacterium avium or M. fortuitum complexes. Fast-atom bombardment mass spectrometry of glycopeptidolipids has proven to be difficult. In this article the cationization method with a metanitrobenzyl alcohol matrix, doped with sodium iodide, is described for analyzing these molecules. The molecular weight of the intact glycopeptidolipids was successfully determined and, using mass-analyzed ion kinetic energy spectrometry, the complete sequences of the peptide and saccharide moieties were elucidated. Moreover, the two structural variants present in these molecules were clearly differentiated. Application of the method showed that the same structural variant occurs in the glycopeptidolipids from two serologically related species of the M. fortuitum complex.

Structures and reactivity of some fluorine-containing gaseous ions

The 70 eV Electron Impact mass spectrometric behaviour of some fluorinated alcohols, i.e. 2-fluoroethan-1-ol, 2,2,2-trifluoroethan-1-ol, 2,3,3,3-tetrafluoropropan -1-ol and 1,3-difluoropropan-2-ol, has been studied in detail by means of mass-analyzed ion kinetic energy spectroscopy, deuterium labelling experiments and comparison with nonfluorinated analogues. Composite metastable peaks related to HF loss have been rationalized by invoking the presence of two concurrent decomposition pathways, the first consisting of a 1–2 elimination and the second requiring the implication of hydroxyl hydrogen. This last process and other decomposition routes suggest the presence of H bridging the hydroxyl oxygen and fluorine.

Electron impact studies of alkanesulfonyl chlorides. An investigation of the sulfur dioxide radical cation

Electron impact mass spectrometry was used to study the fragmentation of a number of alkanesulfonyl chlorides. Mass-analyzed ion kinetic energy (MIKE) spectra of the ionic species obtained after the chlorine atom loss, i.e. [RO 2S] +, showed that the direction of further fragmentation depends on the molecular weight, leading to R + and/or SO + 2 cations. Based on experimental evidence an explanation for this phenomenon is advanced. The electronic excited states of SO + 2 so produced as well as its dissociation to SO + and S + were investigated by means of translational energy (TE) and MIKE spectroscopies respectively, and compared with the analogous data obtained from the SO 2 molecular ion. The TES data pertaining to SO + 2 support the existence of a long-lived non-dissociative electronic excited state at 2.5 ± 0.3 eV above its ground state.

Metastable ion study of organosilicon compounds. Part V—tetramethoxysilane and trimethoxymethylsilane

AbstractThe fragmentations of tetramethoxysilane ((CH3O)4Si (1)) and trimethoxymethylsilane ((CH3O)3SiCH3 (3)) induced by electron impact were investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry and a deuterium‐labelling study. These molecular ions begin to fragment by the loss of CH3 or CH3O. These fragmentations are followed by the loss of an aldehyde molecule (H2CO), as commonly observed in the mass spectra of alkoxysilanes. Almost complete scrambling of the methoxy hydrogens takes place in the metastable molecular ion, [1]+˙, prior to the decomposition. On the other hand, a moderate extent of scrambling of the hydrogens takes place in [3]+˙. The fragmentations of [1]+˙ and [3]+˙ were compared with those of the corresponding carbon analogues, tetramethoxymethane ((CH3O)4C (2)) and 1,1,1‐trimethoxyethane ((CH3O)3CCH3 (4)), respectively.

Remote fragmentations of protonated aromatic carbonyl compounds via internal reactions in intermediary ion-neutral complexes

Protonated aromatic aldehydes and methyl ketones 1a–10a, carrying initially the proton at the carbonyl group, are prepared by electron impact-induced loss of a methyl radical from 1-arylethanols and 2-aryl-2-propanols, respectively. The aryl moiety of the ions corresponds to a benzene group, a naphthalene group, a phenanthrene group, a biphenyl group, and a terphenyl group, respectively, each substituted by a CH 3OCH 2 side-chain as remote from the acyl substituent as possible. The characteristic reactions of the metastable ions, studied by mass-analyzed ion kinetic energy spectrometry, are the elimination of methanol, the formation of CH 3OCH + 2 ions, and the elimination of an ester RCOOCH 3 (R = H and CH 3). The mechanisms of these fragmentations were studied by using D-labeled derivatives. Confirming earlier results, it is shown that the ester elimination, at least from the protonated aryl methyl ketones, has to proceed by an intermediate [acyl cation/arylmethyl ether]-complex. The relative abundances of the elimination of methanol and of the ester decrease and increase, respectively, with the size of the aromatic system. Clearly, the fragmentation via intermediate ion-neutral complexes is favored for the larger ions. Furthermore, the acyl cation of these complexes can move unresitricted over quite large molecular distances to react with the remote CH 3OCH 2-side-chain, contrasting the restricted migration of a proton by 1,2-shifts (“ring walk”) in these systems.

Analysis of a mass‐analyzed ion kinetic energy profile. II. Systematic determination of the kinetic energy release distribution

AbstractA systematic method to evaluate the kinetic energy release distribution from the mass‐analyzed ion kinetic energy (MIKE) spectrum of a metastable ion decomposition, namely lunicolecular fragmentation of lpolyatomic ions, has been ceveloped. The analytical expression for a MIKE profile at a single kinetic energy release developed in lthe preceding paper has been utilized. The present method has been applied to the case of unimolicular dissociation of the t‐butylbenzene molecular ion and to the rather extreme case of a charge‐separation reaction of C7H generated form toluene. Excellent agreements between the experimental data and calculated results have been observed.

Application of collisionally activated decomposition mass-analysed ion kinetic energy spectrometry to a survey of sheep milk for benzimidazole residues in relation to withdrawal periods.

A collisional spectroscopy procedure for simultaneous detection of five widely employed benzimidazole anthelmintics (laevamisole, thiabendazole, mebendazole, fenbendazole, febantel) in sheep milk was developed. The method which involves injection of crude milk extracts and selection and collision of the most abundant ionic species (M+. or fragments) obtained under electron impact ionization, is highly suitable for multi-residue analysis because of its sensitivity (limits of detection in the range of 0.6-2.8 p.p.b) and its rapidity (more than five samples per hour can be processed). The collisional approach was applied successfully for monitoring of anthelmintic residues in sheep milk.

Differentiation of anomericC-glycosides by mass spectrometry using fast atom bombardment, mass-analysed ion kinetic energy and collision-activated dissociation

Positive-ion fast atom bombardment mass spectrometry appears to be a useful method for the differentiation of anomeric C-glycosides. The mass-analysed ion kinetic energy (MIKE) and collision-activated dissociation (CAD) MIKE spectra of selected positive ions can be used as fingerprints of the α- or β-anomers. The main fragmentation routes and particularly the formation of the [M − H]+ ion and the [M + H − PhCH2OH]+ ion were traced for each anomer.

Mass spectrometric investigation of some macrocyclic and macroacyclic compartmental schiff bases

The mass spectrometric behaviour of four macroacyclic and five macrocyclic Schiff bases using two ionization methods (electron impact and fast atom bombardment) was studied in detail with the aid of mass-analysed ion kinetic energy (MIKE) spectrometry. It was possible to propose a common electron impact-induced decomposition pattern for the acyclic compounds, whereas for the cyclic compounds, analysed by fast atom bombardment, peculiar fragmentation routes occurred, which were strongly dependent on the macrocyclic structure and on the different side-chains.

Identification of aminophospholipid stereomers by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis and high-performance liquid chromatography

Two methods for the identification of aminophospholipid stereomers are described. After a chemical derivatization, 9-fluorenylmethoxycarbonyl derivatives of diacyl-sn-2- and diacyl-sn-3-phosphoserine and diacyl-sn-2- and diacyl-sn-3-phosphoethanolamine can be characterized by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis based on the differentiation of relative abundances [M + H + diethanolamine − 89]+ and [M + H]+ fragments derived from [M + H + diethanolamine]+ ions, the protonated solvated molecules, and normal phase high-performance liquid chromatography on the basis of different elution times of the derivatives of the aminophospholipid stereomers on an aminopropyl-bonded column.

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.

Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses

AbstractThe ammonia desorption chemical ionization (NH3‐DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non‐reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH4 – 42]+ ion is not formed direct from [M + NH4]+ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH4+. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH3CO to afford neutral species which complex with NH4+. The structures of the ions resulting from H transfer have been inferred by comparison of their mass‐analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH4]+ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.

Fragmentation ofo-nitrodiarylamines on electron impact: Formation of carbazole radical cations

The HO· fragment eliminated on electron impact (EI) from the molecular ions of o-nitrodiarylamines contains either the amine or the aryl hydrogen. Moreover, 2-phenylamino-3-nitropyridine loses H· from the phenyl group. As confirmed by collision-activated dissociation mass-analysed ion kinetic energy spectra, the fragmentation of such compounds involves the formation of carbazole radical cations. Such a process was not observed for the corresponding o-aminodiarylamines.

Sequential mass spectrometry applied to the study of the formation of “internal” fragment ions of protonated peptides

“Internal” fragment ions of protonated peptides arise by charge retention on a portion of the structure excised from the peptide chain. Their formation appears to be favored by the extented time scale and multiple collision conditions associated with decomposition experiments which use the r.f.-only quadrupole of a hybrid sector/quadrupole mass spectrometer. Sequential product ion scanning and reaction intermediate scanning techniques of MS—MS—MS were used to probe these necessarily multistep fragmentations. With an instrument of BEqQ geometry, mass-analyzed ion kinetic energy spectrometry analyses were used to determine the population of candidate intermediates available for subsequent decomposition to internal fragments in the r.f.-only quadrupole. Reaction intermediate scanning then indicates the relative quantitative significance of competing pathways. In the examples studied, certain Y″-type ions show a high inherent tendency to fragment further to give internal fragments, consistent with the formal equivalence of these intermediates to protonated truncated peptides. Internal fragments can also arise, however, through a number of multistep pathways which can predominate in situations where the requisite intermediates are formed in high abundance.