A.A. Grechnikov - Ph.D. (Chem.), Head of Laboratory, «Energomashtekhnika» (Moscow, Russia); Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences (Moscow, Russia). E-mail: agrech@bk.ru A.S. Borodkov - Research Scientist, «Energomashtekhnika» (Moscow, Russia); Vernadsky Institute of Geo-chemistry and Analytical Chemistry of Russian Academy of Sciences (Moscow, Russia). E-mail: ab-ors@mail.ru S.M. Nikiforov - Senior Research Scientist, A.M. Prokhorov General Physics Institute of Russian Academy of Sciences (Moscow, Russia). E-mail: 15925@mail.ru I.I. Kuzmin - Junior Research Scientist, «Energomashtekhnika» (Moscow, Russia); Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences (Moscow, Russia). E-mail: mcla-ren.ilya@gmail.com

A novel variant of the ionization of chemical compounds, based on a laser-induced electron transfer desorption/ionization (LETDI) is developed. In LETDI, the analyte is deposited on the surface of a specially-designed solid substrate, followed by the exposure of the surface to pulsed laser radiation. Unlike traditional mass spectrometric "soft" ionization methods using pro-ton transfer ionization, this approach uses laser-induced ionization via electron transfer; hence the efficiency of ionization is independent of the analyte basicity, offering the possibility of determination of chemical compounds with low basicity. In this paper, LETDI was tested for the determination of metal coordination compounds. Chlorophyll A (magnesium coor-dination complex, which plays an important role in photosynthesis), platinum complex with 8-mercaptoquinoline (a chem-ical analogue of anticancer drugs) and copper complex with dithizone (a well-known organic reagent for the extraction and concentration of metal ions) were selected as test analytes. The analytical performance of various solid substrates, including stainless steel, graphite, porous silicon and titanium dio-xide was studied. The direct comparison of these substrates for laser-induced electron transfer desorption/ionization of metal complexes reveals that titanium dioxide offer a better choice for determination of metal complexes. It was also shown that the surface morphology does not directly affect the ionization properties of solid substrate in LETDI process. For all studied metal complexes, LETDI mass spectra were recorded and identified. It was found that mass spectra are dominated by the molecular ions for the most abundant peaks. The observed isotope distribution for the molecular ions coincides with the calculated distribution with a good accuracy. Additionally, mass spectra of chlorophyll A and copper complex with dithizone include one peak of metal-containing fragment ions. The LETDI mass spectra are relatively "clean" with low chemical background, except for the peaks corresponding to the ions of sodium and potassium. Based on the actual amount of analyte deposited onto the titanium dioxide surface, the signal-to-noise ratio was estimated. According to the 3σ-criteria, the limits of detection of platinum and copper complexes were found to be 0.3 pg and 15 pg, correspondingly. The presented results clearly show that laser-induced electron transfer desorption/ionization technique allows for highly sensitive detection and identification of metal coordination compounds.

 

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