Probing Coordination Complexes by Carbon Nanotube-Assisted Low-Voltage Paper Spray Ionization Mass Spectrometry.

Fragile transition metal complex ions such as [Cr(H2O)4Cl2](+), difficult to be observed by gas-phase spectroscopy, are detected easily with carbon nanotube (CNT)-assisted low-voltage ambient ionization mass spectrometry. Observation of various substituted ions with D2O and ROH (R = CH3, C2H5, ...) established the versatility of the technique in detecting diverse species. Ligand substitution occurring in solution was captured by the low-voltage technique. The extreme softness of the technique coupled with nanoscale ion sources enabled the creation of such species. Analysis was extended to other halides as well. The intensity of these fragile ions gradually disappeared at voltages beyond 500 V and are completely absent in standard high-voltage ionization. Detection of inorganic complexes further enhances the scope of low-voltage ionization.