MIL-101(Cr) as matrix for sensitive detection of quercetin by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been proven as a useful and advanced technique in the identification of polymers and proteins. However, MALDI-TOF-MS still has the unavoidable drawback of self-signal interference with traditional organic matrices, which could suppress and overlap with the analyte signals in the low-mass region. In this work, MIL-101(Cr), a kind of metal-organic frameworks which possess high molecular weight, π-conjugated 3-D structure, coordinately unsaturated chromium sites (CUS) and strong absorption in the UV range, was employed to replace traditional organic matrices, and it was found that MIL-101(Cr) can dramatically eliminate the background peaks, showing high signal-to-noise level in the analysis of small molecules. As proof-of-concept, quercetin, daidzein, genistein and naringenin, members of flavonol family which widely exists in food and natural products, were successfully determined by utilizing MIL-101(Cr) as the surface-assisted matrix, and the detection of quercetin was sensitive with good salt tolerance and reproducibility. Under optimal conditions, the mass peak intensity exhibited good linear relationships in the range from 0.25µg/mL-7.00µg/mL for quercetin (R=0.996) with detection limit 2.11ng/mL (3σ/k), making the identification of quercetin in sophora japonica successfully. With this strategy we have demonstrated the potentiality of MIL-101(Cr) nanomaterials as MALDI-MS matrix for the detection of small molecules.