The ion kinetic energy spectra of some chlorinated insecticides

The ion kinetic energy (IKE) spectra of the p,p′ and o,p′ DDT, DDD and DDE isomers have been examined. The results indicated that the decomposing [M-CCl₃] ions (b) (m/e 235) for the p,p′ and o,p′ DDT isomers were not energetically similar, suggesting retention of the positional identity of the aromatic chlorine substituents. Similar results were obtained for the [M – CHCl₂] ions (b) for the p,p′ and o,p′ DDD isomers. The IKE spectra of p,p′ and o,p′ DDE were indistinguishable, indicating loss of substituent identity of the aromatic chlorine group. The mechanistic and analytical consequences of these data are discussed. The IKE spectra of the four hexachlorocyclohexane isomers (V to VIII) are different and these spectra are obviously useful in the analysis and characterization of these structurally similar compounds. The differences in their reactivity must in some part be due to their different stereochemical orientations of the chlorine substituents.     

The ion kinetic energy spectra of some aromatic hydrocarbons

The technique of ion kinetic energy spectroscopy has been applied to the study of the aromatic hydrocarbons benzene, toluene, naphthalene, 2-methyl naphthalene, biphenyl and anthracene. The method is illustrated by a complete study of naphthalene in which transitions of metastable doubly- and singly-charged ions are listed, including reactions in which singly-charged ions are formed by collision induced charge-exchange reactions of doubly-charged ions and by the double process of charge-exchange and metastable decomposition with loss of one or two hydrogen atoms. Decompositions of doubly-charged ions into two singly-charged ions, together with the kinetic energies released in these decompositions, are also given for all the compounds studied.     

Interference peaks in mass analysed ion kinetic energy spectra

When mass analysed ion kinetic energy spectroscopy is performed on ions of low abundance and low mass compared with the rest of the ions present in the ion chamber, severe interference may be observed. The major form taken by the interference is of narrow peaks at non-integral mass numbers. Many such peaks can be observed in mass analysed ion kinetic energy spectra and they are mainly attributed to decompositions of metastable ions occurring in the first field free region of the reversed geometry double focusing mass spectrometer.     

The ion kinetic energy and mass spectra of isomeric methyl indoles

The mass spectra of the seven isomeric methylindoles were recorded and the [metastable ion]/[daughter ion] ratios for the reactions m/e 130 → m/e 103 and m/e 103 → m/e 77 have been obtained. The ratios indicate that the decomposing [M — 1] ions (m/e 130) from the 4, 5, 6 and 7 isomers are energetically similar as are the [M — 1] ions from the 2 and 3 isomers. The results observed for the m/e → 103 m/e 77 reaction showed that the decomposing m/e 103 ions from the 2, 3, 4, 5, 6 and 7 isomers all have the same energy distribution. N-Methylindole gave ratios which were similar to the 4 to 7 isomers at 70eV but different at 20 eV. The ion kinetic energy (IKE) spectra of all the isomeric methylindoles were also obtained and the results compared with the data obtained from the [metastable ion]/[daughter ion] approach. The results from the IKE spectra indicated that the energy distributions of the [M — 1] and [(M — 1) — HCN] ions from 1-methylindole and the [(M — 1) — HCN] ions from 2-methylindole could readily be distinguished from other isomers whose [metastable ion]/[daughter ion] ratios were similar. Thus by using both techniques certain ambiguities can be resolved.     

Negative ion field desorption mass spectra of some inorganic and organic compounds

Field desorption of negative ions can be achieved below the threshold of field electron emission. To this end a mixture of the sample with polyethylene oxide and water was applied to smooth wire cathodes. The mass spectra of some inorganic and organic compounds are reported. Anionization by [CI]^? ion attachment is demonstrated with the examples of 20-hydroxycholesterol and sucrose.     

Charge localization: The ion kinetic energy spectra of pyrazine,pyrimidine and pyridazine

The ion kinetic energy (IKE) spectra of pyrazine, pyrimidine, pyridazine, pyrazine-d₄, pyrimidine-d₄ and pyridazine-d₄ have shown that these compounds can more readily be distinguished on the basis of IKE spectra than mass spectra. Studies of the fragmentation of various doublycharged ions have given information about the localization of charge on the heteroatoms and on the structures of the ions themselves. Transition states from which fragmentation occurs for doublycharged ions with loss of either [H]⁺ or [D]⁺ have shown large differences of the order 1 Å between the intercharge distances in the two cases.     

Further interference peaks in mass analysed ion kinetic energy spectra

It is shown that interference peaks in mass analysed ion kinetic energy spectra can also occur from ions decomposing in the accelerating region of the ion source.     

Charge localization—I The ion kinetic energy spectra of ortho-, meta- and para-phenylenediamine

The ion kinetic energy spectra of o-,m-and p-phenylendiamine are presented. Decompositions of doubly-charged ions are given for the three isomers. From the width of the peaks, the energy released is measured and the equivalent intercharge distance is calculated. The results are discussed in terms of possible structures of the various ions. Also, metastable transitions which could give rise to peaks corresponding to energies below that of the mainion beam are listed and the results discussed. Significant differences were observed among the energy spectra of the three isomers.     

The structure of the ion: An ion kinetic energy spectrometry study

The kinetic energy release (T) values for the loss of CO from ions from five compounds have been obtained and are consistent with at least two different structures for the ion. This result is supported by the T value obtained for the decomposition of the molecular ions.     

The ion kinetic energy spectra of isomeric chlorobenzenes and polychlorinated biphenyls (PCB'S)

The ion kinetic energy (IKE) spectra of the isomeric di-and trichlorobenzenes have been examined and the data for the latter compounds suggested that there was incomplete chlorine randomization in their molecular ions in the first field-free region of the mass spectrometer. Previous studies on the mass spectra and [metastable ion]/[daughter ion] ratios of the di-, tetra- and hexachlorobiphenyls (PCB's) indicated chlorine randomization in the molecular ions of those isomers containing less than two chlorine groups ortho to the Ph-Ph ring junction. In contrast the IKE spectra of the isomers are different and the results indicate incomplete chlorine randomization in the first field-free region of the mass spectrometer. These spectral differences may be of some use in PCB analysis.     

Coupling desorption electrospray ionisation and neutral desorption/extractive electrospray ionisation with a travelling-wave based ion mobility mass spectrometer for the analysis of drugs

Desorption electrospray ionisation (DESI) and neutral desorption/extractive electrospray ionisation (EESI) have been coupled to a hybrid quadrupole travelling-wave (T-Wave)-based ion mobility time-of-flight mass spectrometer for the direct accurate mass analysis of active ingredients formulated into pharmaceutical samples. The collision cross-section measurements of polyethylene glycol (PEG) excipients detected in one formulation were estimated and compared with published data. These estimated collision cross-sections of the PEG species showed good agreement with published data.     

Modeling of ion processes in atmospheric pressure matrix-assisted laser desorption/ionisation

Atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) has proven a convenient and rapid method for ion production in the mass spectrometric analysis of biomolecules. This technique, like other atmospheric pressure ionization methods, suffers from ion loss during ion transmission from the atmosphere into the vacuum of the mass spectrometer. In this work, a simple model describing ion formation and ion motion towards the inlet capillary of the mass spectrometer is described. Both the gas flow and electric field near the MALDI plate were numerically calculated using the boundary element method (BEM). The ions were moving along with the gas flow and drifting in the electric field in accordance with their ion mobility properties. The ion signal dependence on an electric field strength obtained in the proposed model correlates well with experimental results.     

A data acquisition system for mass-analyzed ion kinetic energy spectra using a personal computer

An inexpensive data acquisition system has been developed for mass-analyzed kinetic energy experiments which involve scanning the electrostatic analyzer of a reversed geometry mass spectrometer. The various hardware and software design features are described. Results for data obtained with a commercially available VG ZAB-2F mass spectrometer are presented and 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.     

Matrix-assisted laser desorption/ionisation, an experience

MALDI, matrix-assisted laser desorption/ionisation has been a success, no doubt. Together with ESI, electrospray ionization it has revolutionized the analysis of macromolecules from identification to function, the former a key element, e.g. in proteomics, the latter partially still a dream, a not so unrealistic one, though. Thousands of MALDI instruments can be found in research as well as in industrial laboratories all around the globe and even more scientists and developers find it useful in the pursuit of their diverse projects. Once discussed in little attended sessions outside the prime time it is now one of the centers of attention and discussion in literally all conferences on mass spectrometry and increasingly so also on bioanalytics. Yes, MALDI has come of age!