Abstract
Despite various studies of ILs as MALDI matrices, however, so far no relationship has been foundbetween the composition of ILs and their ability to serve as «good» matrices. For a preliminary experiment,in order to evaluate the characteristics of ILs before being used as a matrix in MALDI-MS, it is necessary tostudy the mass spectral behavior for the matrices themselves under LDI conditions. Therefore, the purpose of this work was to analyse ion liquids based on the cation imidazolium in combination with different types ofanions by the LDI method. Ionic liquids were synthesized in the Laboratory of catalytic processes for thesynthesis of organoelement compounds of G.K. Boreskov Institute of catalysis SB RAS (Novosibirsk). Itshould be noted that this ionic liquid was first synthesized in this Laboratory. Analyses were performed usinga Bruker UltraFlex II time of-flight mass spectrometer. Eleven ion liquids based on substituted cation imidazolium in combination with different types of anions were analysed by method laser desorption/ionization in the paper. In all mass spectra of ionic liquids obtained in the positive ion mode, cation produced a major peak and its fragmented ions. Homologous series characterized by the loss of the methyl group have been recorded. According to the more stable carbon-carbon or nitrogen bond in the heterocyclic system than in the carbon-carbon bond in the aliphatic, ion peaks are observed in the mass spectra, characteristic of the loss of methyl fragments from the aliphatic chain. In the LDI spectra obtained in the negative ion mode, the signals of the anions of ionic liquids and their fragments were observed. The combined use of the spectra obtained in positive and negative mode makes it possible to increase the reliability of identification. This makes it possible to use the revealed patterns of fragmentation for the structural analysis of ionic liquids. The analyzed ILs can be used as MALDI matrices, because they do not form dimers, assassinates, are characterized by the absence of adducts with metal ions, which is important for their further use as matrices. BMIMC6F5BF3 was first described by the LDI-MS method. It was shown that the observed fragmentation of the molecular ion of this IL is typical for most ILs with similar cations.
Highlights
Ionic liquids (ILs) are salts in the liquid phase at room temperature with a low melting point
In the case of EMIM, BMIM, C10MIM, C12MIM salts, intensive peaks corresponding to cations are accompanied by additional fragments with m/z 83 caused by loss of ethyl, butyl, decyl and dodecyl, respectively
Homological series characterized by the loss of methyl group are registered in mass spectra, which allows to determine the amount of methyl group fragments in the hydrocarbon substituent, and there is no loss of methyl group from heterocyclic ring
Summary
Ionic liquids (ILs) are salts in the liquid phase at room temperature with a low melting point. ILs have characteristics such as low vapour pressure, non-volatile, good thermal and chemical stability, ability to dissolve compounds of different natures. Ionic liquids are used in different application areas such as analytical chemistry [1,2,3], electrochemistry [4,5], catalysis [6,7] due to its unique properties. ILs are analyzed using various analytical instruments: Ultraviolet-visible (UV-VIS). Spectrophotometry, Fourier transform infrared (FT-IR), nuclear magnetic resonance. Sholokhova et al / Сорбционные и хроматографические процессы.
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