We have developed a new ionization method that uses metal-complex-based ionization probes containing the 2,6-bis(oxazolinyl)pyridine (pybox) ligand, NHS-TMpybox, Mal-TMpybox, BrAc-TMpybox, oxime-TMpybox, and Sar-TMpybox. NHS-TMpybox, Mal-TMpybox, BrAc-TMpybox, and oxime-TMpybox were reacted selectively with the functional groups of biomolecules, whereas Sar-TMpybox was reacted with carbon clusters. These were able to obtain multiply charged ions of target molecules. This method was proven to effectively ionize large complex molecules, including biomolecules and various supramolecules, as well as carbon clusters, such as fullerenes. Moreover, isotope-labeled pybox-La complexes were used to clearly detect isotopic labeling shifts. Their applications to multiply charged ionization, including isotope labeling of biomolecules and carbon clusters using cold-spray ionization mass spectrometry (CSI-MS), are shown.
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