Collisional activation spectra of quarternary ammonium cations produced by field desorption

Collisional activation spectra of quarternary ammonium cations produced by field desorption are reported. The principal fragmentation pathways of these ions are discussed. Furthermore, it is demonstrated that collisional activation in conjunction with field desorption is useful for the elucidation of the structure of complex organic cations.     

Fragmentation patterns by fast linked electric and magnetic field scanning

The fragmentation pattern of the molecular ion of n-octacosane was obtained, with good resolution, by linked scanning of the electrostatic and magnetic fields in a double focusing mass spectrometer in a total scan time of only 30 seconds.     

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.     

Quantitation of isomeric ion mixtures using collisional activation mass spectra

Recently Bass and Bowers have criticized methods for calculation of isomeric composition of gaseous ions based on mass spectra from collisionally activated dissociations (CAD). They fault values from this laboratory on the proportion of benzyl and tropylium ions calculated by two methods from product ion abundances. However, a careful remeasurement of the relevant yields of CAD product ions shows that neither calculation method affected the result outside experimental error, as the ion yields for at least 14 higher energy dissociations are insensitive to both isomeric identity and internal energy. Reducing the [C₇H₇]⁺ internal energy by 1.5 eV does give a 25% reduction in the ion yield for the lowest energy process, supporting the accepted recommendation that these be omitted for quantitative spectral comparisons. A calculation error was made in one of our previous reports on [C₇H₇]⁺, and corrected isomeric composition values are presented. The disparate values from recalculation by Bass and Bowers of other data from this laboratory on [C₂H₄O]^+˙ ions are shown here to be consistent with the large experimental error of those measurements; the medians of their values are actually near the values originally reported. In direct contrast to their assertions, we find no evidence that previous calculation methods have produced misleading conclusions, or that the assumption of linear superposition of CAD spectra in ion mixtures has yielded unreliable results.     

Metastable ion decomposition and collisional activation mass spectra of 1,2,3-triarylpropen-1-ones

Substituents have been found to have a marked influence on the metastable ion decompositions and collisionally activated (CA) fragmentations of the M⁺˙ ion of a number of 1,2,3-triarylpropen-1-ones. An attempt has been made to confirm the structures of the rearrangement ions, [C₁₄H₁₀]⁺˙, [C₁₃H₁₁]⁺˙, [C₁₃H₉]⁺ and [C₁₂H₈]⁺˙ by comparison of their CA spectra with those of the corresponding ions produced from reference compounds. The results imply that [C₁₄H₁₀]⁺˙ and the M⁺˙ ions of phenanthrene and diphenylacetylene have a common structure, [C₁₃H₉]⁺ and the fluorenyl cation have a common structure and [C₁₂H₈]⁺˙ and biphenylene molecular ion have a common structure. The available data indicate that the ion at m/z 167 consists of a mixture of structures, likely possibilities being diphenylmethyl, phenyltropylium and dihydrofluorenyl cations.     

Thermal desorption of cations from polysilicates and zeolites in an external electric field

The desorption of cations from crystalline polysilicates and polysilicic acids, A and Y zeolites, and natural mordenite in the NH₄, H, and dealuminized forms under the action of a strong electrostatic field at temperatures ranging from 20 to 600°C has been studied. The desorption of sodium and potassium cations was detected above a temperature of 150–200°C, and magnesium, calcium, and aluminum cations were not detected. Potassium cations are desorbed at lower temperatures than are sodium cations. Zeolite NaA retains cations more strongly than-does zeolite NaY. The observed spectra are consistent with the concentrations of the cations and the structural features of the samples studied.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 626–629, September–October, 1988.     

Collisional activation spectra at improved resolving power obtained by the use of a collision chamber and a linked scan of the electric and magnetic sector field strengths

A method for obtaining collisional activation spectra at much higher resolving power than before by use of a collision chamber and a B/E linked scan, is described.     

Mass spectrometry and structure of heterocyclic ions by collisional activation.

The fragmentation of isomeric dimethylnitroindolizines due to electron impact was studied by collisional activation and high resolution mass spectroscopy. The [M-OH]⁺ ion which is formed as a result of the ortho-effect was found to have a variable structure. In the case of 2,8-dimethyl-1-nitroindolizine, one of the main fragmentation processes of [M-OH]⁺ is the elimination of an H₂O molecule.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 331–336, March, 1989.     

The field desorption mass spectra of some oligosaccharides and their permethylates and peracetylates

Field desorption mass spectra have been obtained for a number of di-, tri- and tetrasaccharides, and for some permethyl and peracetyl derivatives. The free sugars usually show intense [M + 1]⁺ ions thus enabling the determination of molecular weights. The effect of variation of emitter current on the relative intensities of fragment ions has been investigated. Permethylated oligosaccharides show intense molecular ions; in contrast peracetylated oligosaccharides show only weak molecular ions but strong [M ? 60]⁺ ions. Information from electron-impact and field desorption mass spectra is essentially complementary.     

Comparisom of electron impact and field desorption mass spectra I : Substituted sultams

The low and the high resolution electron impact (EI) and field desorption (FD) mass spectra (MS) of substituted 5- or 6-membered ring sultams are given and the main fragmentation pathways are interpreted. Sultams carrying polar substituents, such as dicarboxylic acids and their mono- and di-amides show either small or no molecular ions with EI-MS. Their existence, however, can be indirectly inferred by metastable defocusing. In contrast to these findings FD-MS display in all our examples the quasimolecular ions (M + 1)⁺ as the base peaks of the spectra. While the pattern for the EI fragmentations follows the generally known rules very closely, five general aspects for the fragmentation pathway of FD mass spectra have been established which demonstrate the characteristics of this modern analytical method. The use of high temperature activated emitters enables a choice to be made between obtaining only molecular peaks and producing significant fragments via a controlled thermal degradation. This is the first time that the complementary and different characters of the information obtained with the two ionization modes EI and FD have been demonstrated on a homologous series of compounds.     

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.     

Mass spectra of substances ionized by fission fragment induced desorption

The mass spectra of substances of physiological and pharmaceutical interest such as steroids, alkaloids, sugars, glycosides and similar, obtained by fission fragment induced desorption as first applied by Macfarlane are presented. The behaviour of organic and inorganic salts is also discussed, including that of mixtures of salts and organic substances. Comparison is made with field desorption data, where available, and electron impact data for those substances of sufficient volatility.     

Analysis of carotenoids by field desorption mass spectrometry

The mass spectra of a variety of authentic carotenoids covering a range of structural types have been studied using the field desorption technique. All the compounds examined show the molecular ion as the base peak, even where this ion is of very low intensity in the electron-impact spectra. Little fragmentation is observed, but thermal decomposition can be induced in certain cases by using higher emitter currents. Application to a simple mixture of authentic compounds and a more complex mixture of sedimentary origin shows the potential of the method in the rapid qualitative screening of carotenoids in crude extracts.     

Temperature dependence of field desorption mass spectra. Investigation of peptide synthesis intermediates

A pulse mode programmer has been developed for field desorption mass spectrometry that provides setting of the emitter heating current during the scans, switching off the emitter heating current during the intervals between consecutive scans and increasing it by 0.5 mA at the start of each scan. Using this heating device, the temperature dependence of field desorption mass spectra of some peptide synthesis products has been studied.     

Comparison of collisional activation spectra of some positive ions produced both by charge reversal of negative ions and by decomposition of positive ions

The charge reversal collision induced decomposition mass analyzed ion kinetic energy spectrum of allyl anion has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of allyl cation and found to be identical except for the presence of +2 ions formed by charge stripping in the spectrum of the [C₃H₅]⁺ ion. Likewise, the collision induced dissociation mass analyzed ion kinetic energy charge reversal spectrum of [CH₃Se]^? has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of [CH₃Se]⁺ and found to be identical. A study of the pressure dependence of the collision induced dissociation mass analyzed ion kinetic energy spectrum of [C₃H₅]⁺ and [C₃H₅]^? showed increasing fragmentation with increasing collision gas pressure, and suggests that a greater mean number of collisions converts more energy to internal modes in the collision induced dissociation mass analyzed ion kinetic energy experiment even at low pressures.     

Mass spectrometric studies of peptides—VI:. Applications of metastable ion and collisional activation spectra

An unambiguous differentiation between leucine and isoleucine residues in peptides is possible with unimolecular metastable ion (MI) and collisional activation (CA) spectra. The immonium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm [Y}\!\mathop {\rm N}\limits^{\rm + } {\rm H = CHC}_{\rm 4} {\rm H}_{\rm 9} {\rm ]} $\end{document}, which is present in the normal mass spectra of all leucine or isoleucine containing peptides, yields MI spectra with which this differentiation can be made with high sensitivity. The MI and CA spectra of other peptide fragments are also applicable in particular cases. MI and CA spectra can also be used to obtain information on the amino acide sequences of individual ions. In general more extensive sequece information is available from CA than from MI spectra. This information appears to be particularly promising for the sequencing of oligopeptide mixtures or of ions produced by field or chemical ionization.     

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.