Molecule/radical reactions prior to ionization under negative chemical ionization conditions

Homolytic reactive mass spectrometry of fullerenes: peculiarities of the reactions of C60 with aromatic compounds in the ionization chambers of mass spectrometers and in solution

C60 reacted with PhH, PhCl, BnH, BnNH2, and o-C2H2B10H10 in the electron impact (EI) ion source of a mass spectrometer at 300 °C forming phenyl, benzyl, and o-carboranyl adducts, respectively, stabilized by hydrogen addition and loss. Besides, the additions to C60 of methyl and phenyl radicals for toluene, and a phenyl radical for benzylamine were observed. A homolytic reaction mechanism was suggested involving the reaction of the radicals formed from the aromatics under EI with C60 at the ionization chamber walls. While the ion/molecule reaction of C60 with benzene performed by Sun et al. under chemical ionization conditions at 200 °C afforded the complex C60•PhH(+•), quite a different isomer, HC60Ph(+•), was detected in the present study as a sequence of the different reaction mechanisms. C60 also reacted with benzyl bromide in the laser desorption/ionization (LDI) source of a mass spectrometer to give C60CPh(+). Phenyl and benzyl derivatives of C60 were found, respectively, when the reactions of the fullerene with PhCl, BnH, and BnBr were performed in solution under ultra violet irradiation. For the reaction with toluene, the strong chemically induced dynamic electron polarization of the intermediate benzylfullerenyl radical with the reverse phase effect was found. The coincidence of the results of the mass spectrometry and solution reactions of C60 with aromatics, even though incomplete, additionally supports the hypothesis, formulated earlier, that the former results can predict the latter ones to a significant extent and shows that this conclusion is valid for both EI and LDI initiated reactions in mass spectrometers.

Homolytic reactive mass spectrometry of fullerenes: interaction of C60 and C70 with ketones in the electron impact ion source of a mass spectrometer and the comparison of results with those of photochemical reactions of C60 with several ketones in solution

Our previous investigations showed that homolytic reactions of C(60) with a number of perfluoroorganic and organomercury(II) compounds occurring under electron impact (EI) in the ionization chamber (IC) of a mass spectrometer could predict the reactivity of C(60) towards these compounds in solution or solid state. To expand the scope of this statement, C(60) and C(70) have been reacted with ketones RCOR(1), where R and R(1) are alkyl, aryl, benzyl, and CF(3), in an IC under EI to yield products of the addition of R(·) and R(1)(·) radicals to the fullerenes, paramagnetic ones being stabilized by hydrogen addition and loss. Experimental evidence in support of a mechanism involving homolytic dissociation of ketone molecules via superexcited states to afford these radicals that react with the fullerenes at the IC surface has been obtained. As anticipated, the reactions between C(60) and several ketones conducted in solution under UV irradiation have afforded Me-, Ph-, and CF(3)-derivatives of C(60). However, some other products have been identified by mass spectrometry and their formation is reasonably explained. When decalin has been employed as a solvent, decalinyl derivatives of the fullerene have been found among the products and the (9-decalinyl)fullerenyl radical has been registered by EPR. Thus, incomplete but reasonable conformity of the results of the reactions of fullerenes with ketones in an IC under EI with those of the reactions of the same reagents in solution under UV irradiation has been demonstrated, and the former results can predict the latter ones to a reasonable extent.

Electron monochromator-mass spectrometer instrument for negative ion analysis of electronegative compounds

Electron monochromators designed for the production of low-energy electrons (0-15 eV) with nearly monoenergetic distributions have been available for many decades. The concept of adapting the electron monochromator as an ion source onto mass spectrometers for the purpose of electron capture negative ion-mass spectrometric (ECNI-MS) analyses is only now being realized. Two different analyzers, a quadrupole and a double focusing sector instrument, have recently been retrofitted with electron monochromators to test their utility as analytical instruments for the detection of environmental compounds and chemical agents. Electron energy scans of compounds in these classes reveal unique negative ion resonances, which can be used as an additional analytical dimension of information for compound identification and confirmation. Electron currents of 430 μA at 0.03 eV electron energy are now available from the electron monochromator, which will provide sufficient electron flux to meet modern standards for trace level analyses. The narrowest electron energy spread achieved has been ±0.07 eV (fwhm). The electron monochromator-mass spectrometer (EM-MS) instrument has been interfaced to a gas chromatograph (GC), and this system (GC/EM-MS) was used to record ion chromatograms of mixtures of polychlorinated compounds. Regioselective ion loss, resulting from dissociative electron capture by the parent molecule, is electron-energy dependent and can be monitored with the EM-MS instrument. Finally, positive ion spectra produced with monoenergetic electrons have also been recorded. © 1997 John Wiley & Sons, Inc.