Paradoxical secondary emission mass spectrum of the leuco form of methylene blue


M.V. Kosevich, O.A. Boryak, V.S. Shelkovsky, V.G. Zobnina, V.V. Orlov

Paradoxical relation between secondary emission mass spectra of methylene blue dye and its leuco form is revealed: while the mass spectrum of the cation of the dye Cat+ (the oxidized form with m. w. 248 Da) reveals an abundant peak of  the product of its reduction at m/z 285, the mass spectrum of its leuco form (the reduced form with m. w. 285 Da) corresponds to the oxidized form dominated by a peak at m/z 284. For the  explanation to this experimental fact it is proposed that oxidation-reduction reactions induced by the ionization agents under secondary emission experiment conditions proceeds in the directions favourable for a given form of the redox-active compound , namely, an oxidized form undergoes reduction, whereas the reduced form is oxidized. Accounting this effect is required for correct identification of redox-active compounds basing on their secondary emission mass spectra, as well as for modelling of oxidation-reduction reactions in the systems containing redox-active dyes under the condition of mass spectrometric experiments.

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