Characterization of Self-Assembling Nano-Sized Structures by Means of Coldspray Ionization Mass Spectrometry

Coldspray ionization (CSI) for mass spectrometry (MS) has been developed and applied to characterize labile self-assembling nano-sized metal complexes. While conventional ESI-MS is not applicable to these compounds because of their instability, CSI affords multiply charged molecular ions with many solvent (acetonitrile) molecules attached. We measured the exact mass of these molecular ions by using crown ether compounds as internal standards. Highly concentrated solutions (ca. 1 mmol/L) of the complexes, whose framework constitution is strongly influenced by concentration, could be used. In the case of some aqueous solutions, the molecular ions could be clearly observed by adjusting the temperature of the desolvation chamber to near the freezing point of water. This CSI-MS should be applicable to a wide variety of labile ionic compounds.