Mass spectral fragmentation pathways in nitroadamantanes. A tandem mass spectrometric collisionally induced dissociation study

A collisionally induced dissociation study of adamantane, 1-nitroadamantane, 1,3-dinitroadamantane and 1,3,5,7-tetranitroadamantane was carried out using tandem high-resolution mass spectrometry. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that the fragmentation of all three nitroadamantanes begins with the consecutive losses of the NO₂ groups followed by fragmentation of the hydrocarbon structure.     

Mass spectral fragmentation pathways in 2,4,6-trinitroaromatic compounds. A tandem mass spectrometric collision induced dissociation study

A collision induced dissociation study of a series of 2,4,6-trinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that dominant fragmentation pathways include loss of OH˙ due to an ortho effect and loss of NO˙ due to the formation of resonance-stabilized products.     

Mass spectral fragmentation pathways in phthalate esters. A tandem mass spectrometric collision-induced dissociation study

A collision-induced dissociation study of a series of phthalate esters was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the phthalates were determined in the electron impact mode. Two major daughter ions are formed, one by a McLafferty rearrangement and hydrogen transfer and the other by loss of an alkoxy radical Another major daughter ion, at m/z 149—which is the base peak in the electron impact mass spectra of most phthalate esters—is being formed through four alternate pathways.     

Mass spectral fragmentation pathways in reduction metabolites of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene. A tandem mass spectrometric collision induced dissociation study

A collision induced dissociation study of a series of reduction metabolites of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the metabolites were determined in the electron impact mode. It was found that the dominant fragmentation pathway is loss of OH^˙ due to an ortho effect. Other fragmentation routes include loss of NO₂˙ and loss of CH₂N˙.     

Mass spectral fragmentation pathways in nitramines. A collision-induced dissociation study

A collision-induced dissociation (CID) study of five synthesized nitramines was carried out using a hybrid EBQQ mass spectrometer. CID spectra were obtained in two modes: B/E linked-scan mode and MS/MS mode using the EB sector combination as the first mass spectrometer and the QQ as collision cell and second mass spectrometer, respectively. Fragmentation pathways of the compounds were determined in the electron-impact mode. It was found that dominant fragmentation pathways included the loss of OH, NO₂ and HNO₂ in addition to the loss of CH₂NNO and CH₂NNO₂.     

Mass spectral fragmentation pathways in some glycoluril-type explosives. A study by collision-induced dissociation and isotope labeling

Electron impact (EI), chemical ionization and negative-ion chemical ionization (NCI) mass spectra of 1,4-dinitroglycoluril (DINGU), its ¹⁵N- and ²H-labeled analogues and the dimethyl-substituted derivatives were recorded. Tandem mass spectrometry with collision induced dissociation was used to study the fragmentation pathways of these compounds. It was found that the main EI fragmentation processes of DINGU are due to the cleavage of C? N bonds and some rearrangement reactions.     

Mass spectral fragmentation pathways in some dinitroaromatic compounds studied by collision-induced dissociation and tandem mass spectrometry

A collision-induced dissociation study of a series of dinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways were determined in the electron impact mode. Loss of NO₂˙ from the molecular ion was observed In most of the investigated compounds. In some compounds loss of NO₂˙ occurred only after loss of OH˙. In other compounds it was not observed at all because of competitive processes, such as loss of NO˙, CO₂, CH₂O, C₂H₄ or H₂O. Loss of NO˙ was a major decomposition pathway, forming ‘dished peaks’ in some of the compounds having a nitro group ortho to a phenyl group, indicating a release of kinetic energy associated with the decomposition. Loss of OH˙ due to an ‘ortho effect’ occurred in compounds where a nitro group was ortho to a group containing a labile hydrogen, but was not observed when competitive processes such as loss of NO˙, NO₂˙ or H₂O occurred. ‘Nitro to nitrite’ isomerization was suggested to explain the decarboxylation process in 2,4- and 2,5-dinitrobenzoic acid and the loss of COH₂ in 2,4-dinitroanisole.     

Mass spectrometric fragmentation of the tautomers of 1,3-diketones. A gas chromatographic/mass spectrometric study

The diketo and ketoenol tautomers of aliphatic 1,3-diketones can be easily separated by gas chromatography. The mass spectra of tautomers of pentane-2,4-diones substituted at C(l) and C(3), separated in this way, have been obtained. The fragmentation mechanisms are discussed. The mass spectra of the tautomers are quite different, and the main fragmentation pathways can be easily linked to the structures of the (non-interconverting!) tautomeric molecular ions. Furthermore, isomers differing by the position of the substituent can also be identified by their mass spectra.     

Mass spectral fragmentation pathways in 2,4,6-trinitrotoluene derived from a MS/MS unimolecular and collisionally activated dissociation study

The fragmentation pathways of 2,4,6-trinitrotoluene have been examined using ¹⁵N and ²H isotopic labelling in conjunction with tandem mass spectrometry. Both the unimolecular and collisionally activated decomposition modes were investigated. Fragmentation pathways were established in both modes and isotopic shifts were used to determine the groups lost. The major pathways include the loss of OH or H₂O, followed by the subsequent loss of NO or NO₂. There is virtually no ring disintegration until the majority of the attached groups are lost.     

Electron impact mass spectra of some anthracene,anthrafuran and nitroanthrafuran derivatives. A tandem mass spectrometric collisional activation dissociation study

The 70-eV electron impact mass spectra of a series of thirty anthracene, seven anthra[2,1-b]furan and seven 2-nitroanthra[2,1-b]furan derivatives are described and discussed. A collisional activation dissociation study of 1-formyl-2,6-dimethoxy-9-methyianthracene, 1-formyl-2,6-dimethoxy-10-methylanthracene, and 2-carboxy-11-methylanthra[2,1-b]furan has been carried out using tandem mass spectrometry in order to substantiate the fragmentation schemes.     

Electrospray ionization ion trap multiple-stage mass spectrometric fragmentation pathways of leucine and isoleucine: an ab initio computational study

We recently demonstrated the possibility to distinguish between leucine and isoleucine in several tryptic peptides by means of consecutive tandem mass steps (Armirotti et al. J. Am. Soc. Mass Spectrom. 2007; 18: 57), exploiting a gas-phase rearrangement of the immonium ion of Ile. In the present paper we explore the tandem mass spectrometric behaviour of the two amino acids. We propose a plausible structure for the diagnostic m/z 69 ion of Ile, that was reported for the first time in 1996 (Hulst and Kientz J. Mass. Spectrom. 1996; 31: 1188), and we explain why its formation is favoured with respect to Leu. Our conclusions are supported by ab initio quantum chemistry calcultations and isotope-labelled standards experiments.     

Mass spectral fragmentation pathways in cyclic difluoramino and nitro compounds

The recently synthesized compounds 4, 4-bis(difluoramino)-1-nitropiperidine (I), 1,4,4-trinitropiperidine (II), 1,1,4,4-tetranitrocyclohexane (III), 1,1,4, 4-tetrakis(difluoramino)cyclohexane (IV) and 3,3,7, 7-tetrakis(difluora-mino)octahydro-1,5-dinitro-1,5-diazocine (HNFX, V) are being considered as potential energetic materials. The mass spectra of these compounds were studied using electron ionization (EI) mass spectrometry. A collision-induced dissociation (CID) study of the major EI peaks was carried out using a Finnigan TSQ 700 tandem mass spectrometer. The mass fragmentation pathways are constructed and discussed. The decomposition of HNFX (V), under EI, appeared to parallel the thermal decomposition of nitramines where N-NO(2) cleavage is often the first step. However, the two nitramines with a six-membered ring structure (I and II) underwent initial loss of a geminal substituent; loss of a nitramine nitro group was the secondary step. The two cyclohexane structures (III and IV) showed similar initial fragmentation pathways, featuring successive losses of nitro or difluoramino groups. Copyright 2000 John Wiley & Sons, Ltd.     

A novel tandem quadrupole mass spectrometer allowing gaseous collisional activation and surface induced dissociation.

A novel tandem quadrupole mass spectrometer is described that enables gaseous collision-induced dissociation (CID) and surface-induced dissociation (SID) experiments. The instrument consists of a commercially available triple quadrupole mass spectrometer connected to an SID region and an additional, orthogonal quadrupole mass analyser. The performance of the instrument was evaluated using leucine-enkephalin, allowing a comparison between CID and SID, and with previous reports of other SID instruments. The reproducibility of SID data was assessed by replicate determinations of the collision energy required for 50% dissociation of leucine-enkephalin; excellent precision was observed (standard deviation of 0.6 eV) though, unexpectedly, the reproducibility of the equivalent figure for CID was superior. Several peptides were analysed using SID in conjunction with liquid secondary-ion mass spectrometry or electrospray; a comparison of the fragmentation of singly protonated peptide ions and the further dissociation of y-type fragments was consistent with the equivalence of the latter fragments to protonated peptides. Few product ions attributable to high-energy cleavages of amino acid side-chains were observed. The SID properties were investigated of a series of peptides differing only in the derivatization of a cysteine residue; similar decomposition efficiencies were observed for all except the cysteic acid analogue, which demonstrated significantly more facile fragmentation.     

Liquid chromatography ion trap/time-of-flight mass spectrometric study on the fragmentation of an acetildenafil analogue

Liquid chromatography ion-trap time-of-flight mass spectrometry was employed to elucidate the fragmentation pathways of an analogue of acetildenafil. Based on the accurate masses of the parent ion, product ions and neutral losses of acetildenafil analogue, its fragmentation pathways were proposed. The information is useful for the on-line structural identification of unknown analogues of acetildenafil found as adulterants in herbal products.     

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 + NH₄]⁺ or [M + CH₃NH₃]⁺, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH₃) or CI (CH₃NH₂) 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.     

Nitramine anion fragmentation: A mass spectrometric and Ab initio study

The fragment ion formation characteristics of the radical anions generated from hexahydro-1,3,5-trinitrotriazine (RDX) and its three nitroso metabolites were studied using GC/MS with negative chemical ionization (NCI) to understand the fragmentation mechanisms responsible for the formation of the most abundant ions observed in their NCI mass spectra. Ab initio and density functional theory calculations were used to calculate relative free energies for different fragment ion structures suggested by the m/z values of the most abundant ions observed in the NCI mass spectra. The NCI mass spectra of the four nitramines are dominated by ions formed by the cleavage of nitrogen-nitrogen and carbon-nitrogen bonds in the atrazine ring. The most abundant anions in the NCI mass spectra of these nitramines have the general formulas C(2)H(4)N(3)O (m/z 86) and C(2)H(4)N(3)O(2) (m/z 102). The analyses of isotope-labeled standards indicate that these two ions are formed by neutral losses that include two exocylic nitrogens and one atrazine ring nitrogen. Our calculations and observations of the nitramine mass spectra suggest that the m/z 86 and m/z 102 ions are formed from either the (M--NO)(-) or (M--NO(2))(-) fragment anions by a single fragmentation reaction producing neutral losses of CH(2)N(2)O or CH(2)N(2)O(2) rather than a set of sequential reactions involving neutral losses of HNO(2) or HNO and HCN.     

The fragmentation of aliphatic ketones in the mass spectrometer: A detailed study of nonan-4-one using ion kinetic energy spectroscopy

The ion kinetic energy (IKE) spectra of nonan-4-one, 7,7-d₂-nonan-4-one and 1,1,1-d₃-nonan-4-one have been recorded and interpreted. The various fragmentations observed in the IKE spectra have been confirmed and some new fragmentations found by carrying out high voltage scans with the magnetic field set successively to collect ions at each mass to charge ratio throughout the mass spectrum. Several new fragmentation modes have been discovered, and their significance is discussed.     

Kinetic energy release in metastable ion transitions. A study by ion kinetic energy spectrometry and rrkm theory

An approach to energy partitioning using experimental data in conjunction with theoretical calculations is presented, with the McLafferty and related rearrangements occurring in the molecular ions of ketones, esters, amides and acid chlorides representing the specific reactions examined. The kinetic energy release associated with statistical partitioning of the nonfixed energy of the activated complex was calculated from unimolecular reaction theory and compared with experimental data. Calculations of the energy dependence of the rate constant and the average statistically released kinetic energy were made for 24 activated complexes corresponding to the two basic structures, cyclic and linear. The frequencies used in the calculations were all modeled upon the 2-pentanone case with sufficient variation in the frequencies used to allow for any reasonable type of perturbation of the linear and cyclic structures. To further test that the complexes chosen were reasonable, A-factors were determined. From a comparison of the calculated and experimental results, the contributions of the nonfixed energy of the activated complex and of the reverse activation energy to the energy release were separated. This appears to be applicable, not only to the 2-pentanone case, but across the series of reactions studied. It is also shown that, despite the fact that these reactions release relatively small kinetic energies, the fraction due to the reverse activation energies may be large. The consequences of these observations for ion enthalpy determinations are emphasized.     

Electron impact,chemical ionization and negative chemical ionization mass spectra,and mass-analysed ion kinetic energy spectrometry–collision-induced dissociation fragmentation pathways of some deuterated 2,4,6-trinitrotoluene (TNT) derivatives

Mass-analysed ion kinetic energy spectrometry (MIKES) with collision-induced dissociation (CID) has been used to study the fragmentation processes of a series of deuterated 2,4,6-trinitrotoluene (TNT) and deuterated 2,4,6-trinitrobenzylchloride (TNTCI) derivatives. Typical fragment ions observed in both groups were due to loss of OR′ (R′ = H or D) and NO. In TNT, additional fragment ibns are due to the loss of R₂′O and 3NO₂, whilst in TNTCI fragment ions are formed by the loss of OCI and R₂′OCI. The TNTCI derivatives did not produce molecular ions. In chemical ionization (Cl) of both groups. MH⁺ ions were observed, with [M – OR′]⁺ fragments in TNT and [M – OCI]⁺ fragments in TNTCI. In negative chemical ionization (NCI) TNT derivatives produced M^?′, [M–R′]^?, [M–OR′]^? and [M–NO]^? ions, while TNTCI derivatives produced [M–R]^?, [M–Cl]^? and [M – NO₂]^? fragment ions without a molecular ion.