Suitability of TiO2 nanoparticles and prolate nanospheroids for laser desorption/ionization mass spectrometric characterization of bipyridine-containing complexes

Nanostructured materials as substrates for surface-assisted laser desorption and ionization time-of-flight mass spectrometry have two main advantages such as small number of signals in the low mass range and salt tolerance. We have also previously observed decreased extent of undesired fragmentation of bipyridine-containing transition metal complexes in the presence of TiO2 nanoparticles (NPs). In this work, we extended our previous study and tested whether both TiO2 NPs and TiO2 prolate nanospheroids (PNSs) can be used as substrates for SALDI-MS of bipyridine-containing transition metal complexes and whether they tolerate intense laser and the presence of inorganic salts. TiO2 NPs (an average diameter of 5 nm) and PNSs (length: 40-50 nm, the lateral dimension: 14-16 nm) were characterized microscopically and their mass spectra were analyzed, as well as the spectra of bipyridine-containing Pt(II) and Ru(III) complexes. Our results show that seven times higher analyte signals can be obtained in the presence of PNSs compared to the signals acquired with NPs and three times higher compared to spectra acquired without a substrate. The presence of inorganic salt did not affect the spectra, which makes both TiO2 nanocrystals suitable for MS analysis of transition metal complexes in biological fluids. (C) 2015 Elsevier B.V. All rights reserved