Determining enediol compounds in tea using surface-assisted laser desorption/ionization mass spectrometry with titanium dioxide nanoparticle matrices

We describe the use of titanium dioxide nanoparticles (TiO₂ NPs) as selective probes and matrices for the determination of catechins using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The interactions between the enediol compounds and TiO₂ NPs were evident by the change in color of the TiO₂ NP solution from milky white to orange. Through these interactions, the TiO₂ NPs could be used to concentrate enediol compounds, including catechins and ascorbic acid. The limits of detection (LODs) for three catechins - catechin, (-)-epigallocatechin, and (-)-epigallocatechin gallate - at a signal-to-noise ratio of 3 were 0.45, 1.85 and 0.65 μM, respectively. The TiO₂ NP matrices provide a number of advantages over conventional organic matrices (e.g. 2′,4′, 6′-trihydroxyacetophenone), including ease of sample preparation, less background noise in the low-mass region, and high repeatability. The applicability of this method was confirmed through the high reproducibility of the determination of the two catechins in tea samples that had not been subjected to any sample preparation procedures (shot-to-shot variation: <10%).