Intact Cation Research Articles

In-beam electron ionization and mass analyzed ion kinetic energy studies on choline and several long chain aliphatic quaternary ammonium salts.

In-beam electron ionization (EI) and mass analyzed ion kinetic energy (MIKE) spectrometric techniques were used to study the EI-induced fragmentation of choline iodide, choline chloride, hexadecyltrimethylammonium bromide, ethylhexadecyldimethylammonium bromide, and methyltricaprylammonium chloride. The in-beam EI and MIKE spectra of these compounds are presented. The in-beam EI spectra exhibit intact quaternary ammonium cations as well as thermally and EI-induced fragment ions. The fragmentation pathways arising from the intact cations in the in-beam EI spectra were defined by using the MIKE technique. The general fragmentation processes are similar to those of simple tetraalkylammonium cations previously reported. The inbeam EI spectra of a sample of tricaprylmethylammonium chloride exhibit abundant ions that are due to lower and higher homologous cations, indicating that the sample is a mixture of at least three homologs.

Fast atom bombardment mass spectrometry of related Cu(I) and Cu(II) chelates

The reactions of a series of Cu(I) and Cu(II) complexes containing pyrazolyl or dimethylpyrazolyl residues in the ligands during the ionization process were studied by fast atom bombardment mass spectrometry. Complexes with a +1 charge produce intact cations. Those with a higher charge yield +1 cations by formal reduction or by clustering with anions, sometimes by several simultaneous processes. Neutral complexes are protonated to give +1 ions.

Analysis of organic quaternary ammonium salts by LAMMA

The application of the laser microprobe mass analyser (LAMMA) to several acyclic quaternary ammonium salts with aliphatic and aromatic substituents was investigated. The LAMMA spectra share some typical features with the ones, obtained by mass spectrometric (MS) analysis using soft ionisation techniques, e. g. the intact cations are detected as well as the iminium ions, issued from their decomposition. However, as a result of the abundant fragmentation and because of the presence of additional characteristic peaks, LAMMA spectra become largely comparable to the ones, recorded on a conventional MS with electron impact-ionisation and sample introduction by direct probe, though it is well known that the latter method induces thermal degradation of these salts and consequently only allows for the detection of the corresponding decomposition products.

Ribosyl-diphthamide: Confirmation of structure by fast atom bombardment mass spectrometry

Diphtheria toxin inactivates protein synthesis elongation factor 2 by attaching ADP-ribose to an unusual post-translational amino acid derivative, diphthamide, in the factor. Previously, we prepared ribosyl-diphthamide from the ADP-ribosyl-factor and proposed on the basis of NMR spectral analysis that it is 1-α- d-ribofuranosyl-2-[3-carboxyamido-3-(trimethylammonio)propyl]histidine [N. J. Oppenheimer, and J. W. Bodley, (1981) J. Biol. Chem. 256, 8579–8581 and op. cit.]. Now, using fast atom bomardment mass spectrometry, the intact cation of ribosyl-diphthamide has been observed in the gas phase. The theoretical mass of the structure proposed for ribosyl-diphthamide uniquely agrees with the observed mass of the inact cation of the compound to within 2 ppm. Collisional activation decomposition mass spectral analysis provided additional structural confirmation. Thus, although the compound has not been synthesized, all available evidence appears uniquely consistent with the structure of ribosyl-diphthamide previously proposed.

MS/MS spectra of organic ions generated by secondary ion mass spectrometry

Organic ions are withdrawn directly from the condensed phase in molecular secondary ion mass spectrometry (SIMS). In common with other desorption ionization methods, SIMS provides both molecular weight and structural information about complex molecules; other characteristics include a persistence of ion emission, a propensity for cluster ion formation, and a sensitivity to matrix effects. Tandem mass spectrometry (MS/MS) can be advantageously coupled with SIMS to establish ionic relationships in the gas phase, to deduce ion structure, and in analytical studies. In this work, capabilities for isomer differentiation are demonstrated in the natural products field, the value of solid matrices in desorption ionization is illustrated, and in situ isotopic selection is used to interpret spectra. Various types of cluster ions generated in SIMS are analyzed by MS/MS, which allows a distinction between weakly and strongly bound complexes. The cluster ions formed between the cation of thiamine and glycerol shows a strong sample/solvent interaction and consequently glycerol is too reactive a solvent to be used in obtaining the mass spectrum of thiamine. Gas phase fragmentations of the intact cation of carnitine are strikingly different from those observed in the SIMS spectrum, in contrast to the behavior of thiamine, cocaine and candicine for which collision-induced dissociations provide a good guide to desorption ionization mass spectra.

Enhanced ionization of organic salts in secondary-ion mass spectrometry

Ammonium chloride increases the absolute signal intensity for the intact cations of organic ammonium, pyrylium and phosphonium salts when admixed in 10−10 3-fold excess. This signal enhancement results in improved signal-to-noise ratios and is achieved without addition of extraneous ions to the spectrum. The ionization efficiency (secondary ions produced per incident primary ion) is similar for neat and ammonium chloride diluted samples. However, the ionization yield (secondary ions produced per sample molecule) is enhanced by the matrix by four orders of magnitude. Sensitivity, calculated here for a desorption ionization method, is 0.5−1 × 10 −10 C μg −1, and is less than that of electron ionization and chemical ionization sources. Spectra of submicrogram amounts of organic species in ammonium chloride are stable and can be recorded continuously for many hours, as compared to less than an hour for the neat compounds. Even subnanogram amounts of sample diluted in ammonium chloride give spectra which last a number of minutes. Matrix-diluted samples may be withdrawn from the spectrometer and stored for days before being reanalyzed without incident. With this matrix, the technique is essentially nondestructive. Total ionization yields for matrix-diluted samples are estimated at 0.01-0.1%. Primary-ion fluxes impinging on matrix-diluted samples exceed static SIMS limits without evidence of beam damage.

Desorption ionization mass spectrometry: Secondary ion mass spectra of phosphonium salts

Secondary ion mass spectra are obtained for involatile phosphonium salts not analyzable by conventional ionization methods. The spectra typically exhibit an abundant intact cation and fragment ions which result from predictable losses of stable neutral species from the cation. A systematic pattern of fragmentation occurs in simple salts which serve as model compounds, and also more complex structures which are of pharmaceutical interest. Close parallels with the behavior of related volatile compounds in electron and chemical ionization mass spectrometry are observed in the presence of characteristic fragment ions and a tendency for rearrangement with elimination of stable molecules. Doubly charged salts undergo loss of a charged fragment such as a proton to give stable singly charged species. Sensitivity is such that a few nanograms of phosphonium salt suffices to provide a spectrum observable for ten to twenty minutes. The preferential desorption of precharged species makes possible the direct analysis of these salts in Chromatographic media, including electrophoresis membranes, and also the direct desorption of these salts from vacuum compatible solutions.

Secondary ion mass spectra of quaternary pyridine aldoximes

The secondary ion mass spectra (s.i.m.s.) of the most widely used therapeutic monoquaternary pyridine aldoximes and diquaternary pyridine aldoximes, as well as some related monoquaternary ammonium salts and neutral oximes, are reported. The monoquaternary derivatives of the oximes yield prominent intact cations which provide molecular weights, and fragmentation patterns which are dominated by even-electron ions. The diquaternary oximes investigated do not give dications, but rather undergo charge separation reactions sometimes accompanied by intramolecular aromatic substitution, and they sometimes yield monoquaternaries by expulsion of a proton. The s.i. mass spectra are structure-specific for the monoquaternary salts, allowing isomer distinction in the cases examined. Quaternary salts can be quantified by s.i.m.s., and low detection limits (less than 50 ng) are demonstrated here for the oxime salts; thus s.i.m.s. is an appropriate analytical technique for the title compounds. Procedures of derivatization which convert the neutral amines to ionic compounds, such as quaternization with alkyl halides, provide a simple means of obtaining high-quality s.i.m.s.

Solid solution formation in the U 3O 8 → UO 2 transformation

Possibilities were investigated for incorporation of various foreign elements into the crystal lattice of uranium dioxide during its formation in U 3O 8 → UO 2 transformation carried out under the following conditions : Arc-ignition in various gas environments (A, N 2, CO 2, H 2) of U 3O 8-metal oxide mixtures in a graphite electrode, under conditions analogous to those of the spectrochemical analysis of uranium. It has been found that in the rapid and complete U 3O 8→ UO 2 transformation thereby made possible, foreign elements present are incorporated to a limited extent into the lattice of the uranium dioxide formed. For specimens arced in N 2, maximum concentrations retained in solid solutions with UO 2 were: 13 mole % CdO; 4 mole % ZnO; 4 mole % MgO; 7 mole % Bi 2O 3; 1 mole % PbO; 0.1–0.4 mole % CaO, In 2O 3 or NiO; ThO 2 and La 2O 3 were not found to enter UO 2 lattice, but arc-ignition of a U 3O 8-La(NO 3) 3·6H 2O mixture resulted in ready solid solution formation. On the basis of density measurements of solid solutions containing CdO and ZnO respectively, it was concluded that fluorite-type substitutional solid solutions were formed with intact cation lattice, the anion lattice probably remaining intact as well. For specimens arced in H 2, capacity for solid solution formation is reduced. The factors influencing the behaviour of the foreign metal oxides in mixtures with U 3O 8 under investigated conditions are discussed. The possibility of solid solution formation of UO 2 with certain less stable oxides, employing rapid U 3O 8→ UO 2 transformation, is pointed out.