Graphene flakes enhance the detection of TiO2-enriched catechins by SALDI-MS after microwave-assisted enrichment

•A novel method for the rapid detection of catechins in tea leaves using SALDI-MS.•TiO2–GF mixture resulted in better enrichment and ionization efficiency.•GF in TiO2–GF assist in the microwave-assisted enrichment and the SALDI sensitivity.•This approach provides good quantitative linearity and reproducibility.

In this study, we describe a novel method for the rapid detection of catechins in tea leaves using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The method involves incubating catechins in a mixture of titanium dioxide (TiO2) nanoparticles and graphene flakes (GF) and then subjecting the mixture to microwave irradiation to facilitate the enrichment of analytes. In this approach, TiO2 nanoparticles serve as probes to enrich catechins while GF serve to increase the desorption/ionization efficiency. The use of the TiO2–GF mixture as matrix provides a number of advantages over TiO2 nanoparticles alone, including higher desorption/ionization efficiency, enhanced analyte enrichment and reduced run time (less 10 min). We demonstrate that the addition of GF to nanoparticles of TiO2 improves the detection of catechins by SALDI-MS. At a signal-to-noise ratio of 3, the limits of detection were 0.04 pmole for (+)-catechin (C), 0.17 pmole for (–)-epigallocatechin (EGC), 0.35 pmole for (–)-epicatechin gallate (ECG), and 0.50 pmole for (–)-epigallocatechin gallate (EGCG). This method was further applied to determine the catechin content in several tea samples and the results showed good shot-to-shot and sample-to-sample reproducibility (less than 10% and 13%, respectively) as well as good quantitative linearity for the four analytes (R2>0.995). The precision calculated as percent relative standard derivation (%RSD), ranged from 3.6% to 12.4%. Overall, we show that this method is a sensitive, simple and high-throughput technique for the detection of catechins in tea.

Graphical abstractThe selective process for the enrichment of catechins with TiO2 nanoparticles-graphene flakes (GF) mixture and microwave irradiation acceleration, and it can be analyzed with SALDI directly.Figure optionsDownload full-size imageDownload as PowerPoint slide