SALDI-TOF-MS analyses of small molecules (citric acid, dexasone, vitamins E and A) using TiO2 nanocrystals as substrates

Abstract

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 (TiO2) 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 TiO2 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. TiO2-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 TiO2 nanocrystals of various shapes and dimensions, i.e. the colloidal TiO2 nanoparticles (TiO2 NPs), TiO2 prolate nanospheroids (TiO2 PNSs) and TiO2 nanotubes (TiO2 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 TiO2 nanocrystals depends on the analyte. Signals which are acquired with the assistance of TiO2 PNSs have the highest sensitivity and reproducibility (the smallest standard deviation), even compared with those in the LDI mode. This implies that TiO2 PNSs could also be suitable for quantitative analyses of small molecules.

Exploring the potential of laser desorption ionisation time-of-flight mass spectrometry to analyse organic capping agents on inorganic nanoparticle surfaces

“…However, on Ag NPs, neither the [CA + H] + ion was detected (Fig. 1b ) nor previously reported sodium adducts [CA + Na] + or [CA-H + 2Na] + [ 20 ] which could be formed since these NPs are dispersed in 2 mM sodium citrate.…”

“…The calculated mass errors are shown in ESM Table S1. [20] which could be formed since these NPs are dispersed in 2 mM sodium citrate.…”

“…Our identified signals for the small molecules used here are not reported in literature with LDI-MS. However, our observed fragment ions for CA, TA and LA have been identified as characteristic mass spectrometry fragments for these compounds [ 20 , 23 – 25 ]. However, the ion formation is not only solely dependent on the type of capping agent but also on the core material.…”

Nanomaterials as Assisted Matrix of Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for the Analysis of Small Molecules

“…In generally, the best reproducibility was obtained with the larger nanocrystals, TiO 2 PNSs and TiO 2 NTs, making them good candidates for the quantitative determination of small molecules. However, for analysis of citric acid, dexasone, vitamins E and A, PNSs provided the highest sensitivity and reproducibility [71]. …”

TiO2 Nanocoral Structures as Versatile Substrates for Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry

“…TiO 2 occurs naturally as three polymorphs: anatase, brookite, and rutile, and these have different chemical and physical properties. To date, several SALDI‐MS analyses with TiO 2 substrates have been reported . Kawasaki et al.…”