SALDI-TOF-MS analyses of small molecules using TiO.sub.2 nanocrystals as substrates

• Published in: Analytical and bioanalytical chemistry 2016-10, Vol.408 (26), p.7481
• Main Authors: Popovic, Iva A, Nesic, Maja, Vranjes, Mila, Saponjic, Zoran, Petkovic, Marijana
• Format: Article
• Language: English
• Subjects: Chemical properties; Citric acid; Methods; Time-of-flight mass spectrometry; Titanium dioxide; Vitamin A; Vitamin E
• ISSN: 1618-2642
• DOI: 10.1007/s00216-016-9846-8

Surface-assisted laser desorption/ionisation time-of-flight mass spectrometry (SALDI-TOF-MS) might be the method of choice for the analysis of low mass molecules (less than m/z 500). Titanium dioxide (TiO.sub.2) nanocrystals as a substrate for SALDI-TOF-MS improve the reproducibility of the signal intensities and prevent the fragmentation of some molecules upon laser irradiation, as we have previously shown. In addition, variously shaped and sized TiO.sub.2 nanocrystals/substrates for SALDI-MS could be used for quantification of small molecules, which are otherwise difficult to detect with the assistance of organic matrices. TiO.sub.2-assisted LDI-MS spectra could be acquired with excellent reproducibility and repeatability and with low detection limit. In the current study, we analysed the spectra of dexasone, citric acid, vitamin E and vitamin A acquired with TiO.sub.2 nanocrystals of various shapes and dimensions, i.e. the colloidal TiO.sub.2 nanoparticles (TiO.sub.2 NPs), TiO.sub.2 prolate nanospheroids (TiO.sub.2 PNSs) and TiO.sub.2 nanotubes (TiO.sub.2 NTs). Various shapes and dimensions of substrates were used since these factors determine desorption and ionisation processes. The homogeneity on the target plate was compared based on signal-to-noise values of peaks of interest of analysed molecules as well as the within-day and day-to-day repeatability. In summary, the obtained results show that the applicability of individual TiO.sub.2 nanocrystals depends on the analyte. Signals which are acquired with the assistance of TiO.sub.2 PNSs have the highest sensitivity and reproducibility (the smallest standard deviation), even compared with those in the LDI mode. This implies that TiO.sub.2 PNSs could also be suitable for quantitative analyses of small molecules.