Mass spectrometric investigation of metallothionein and ionic liquids using electrospray ion source coupled with quadrupole ion trap mass analyzer.

摘要

Electrospray is a well-developed ionization technique for transferring intact dissolved molecules from liquid into the gas-phase through a capillary emitter. As a 'soft' ionization method, intact molecules are transformed and are ready for mass identification and structure characterization. Quadrupole ion traps are versatile mass analyzers and are well-known for the capability to perform tandem mass scans by which the structural information can be obtained.;Collision-induced dissociation (CID) is applicable used in quadrupole ion trap to produce fragment ions. Metal-protein bond dissociation properties were studied by the tandem mass spectrometry. Binding properties of metal ions and ligand groups on peptide chains were studied. The chelating reagent EDTA was used to confirm the production of the free metal ions formed in the CID process by capturing them and forming complex ions which were detectable by the ion trap mass analyzer based on their large m/z values.;Negative ion mode electrospray mass spectrometric studies of undiluted ionic liquid reveal the influence of water on the observed gas-phase population. Anions observed in addition to the pre-existing hexafluorophosphate anion result from a series of reactions initiated by hydrolysis of hexafluorophosphate. The mass spectral response shows a quantitative logarithmic relationship between signal intensities and the amount of water present, against which the water content could be rapidly assessed.;Positive ion mode electrospray mass spectrometric analysis of room temperature ionic liquids shows fragmentation of dialkylimidazolium cations resulting from alkyl elimination reactions that yield an N-methylimidazolium cation and a neutral alkene. This unimolecular dissociation reaction requires the formation of a cyclic transition state involving a proton on the leaving alkyl chain. The same process was observed in low energy collision-induced dissociation reactions of the isolated precursor ion in tandem mass spectrometry experiments.;The measurement of difference between the gas-phase ion intensity and the concentration of the solution provides an interesting approach to mass-analysis of the dissolved analytes in undiluted ionic liquids. Electrospray behavior of solution of neutral ferrocene and ferrocenium salt dissolved in ionic liquids is studied.