Amorphous Titanium\nDioxide Nanoparticles and Their\nUnexpected Fragmentation in MALDI-TOF/MS

Amorphous 3 nm large ultrasmall (<i>us</i>TiO<sub>2</sub>) and 7 nm large anatase (<i>n</i>TiO<sub>2</sub>) nanoparticles\n(NPs) were successfully prepared and characterized by TEM, FTIR, DRX,\nUV–vis, and DLS techniques. The MALDI-TOF/MS was shown to be\neffective in assessing the surface chemistry but fragmentation processes\nprecluded its use for evaluation of particle size distribution. In\nfact, the laser causes the fragmentation not only of amorphous TiO<sub>2</sub> NPs but also of the material subjected to heat treatment\nand crystallization at 450 °C for 4 h upon interaction with the\nDHB matrix and TFA ionizing agent. No significant difference could\nbe observed in the spectrum by varying the particle size, indicating\nthe high stability of the TiO<sub>2</sub> dimer and its low aggregates\nin the gaseous phase. In short, MALDI-TOF/MS is effective for the\ndirect analysis of nanoparticle surfaces, especially the interaction\nof functionalizing molecular species with the inorganic components,\nwhich in combination with the other techniques demonstrated to be\nideal for the detailed characterization of nanomaterials.