Mixed valence state cerium metal organic framework with prominent oxidase-mimicking activity for ascorbic acid detection: Mechanism and performance

It is indispensable to establish a simple, effective and accurate method for ascorbic acid (AA) detection since it plays a crucial role in human health. Herein, a novel oxidase mimic of mixed valence state cerium metal organic framework (MVCM) was successfully synthesized by in-situ partial oxidation of cerium metal organic framework (Ce-MOF). On account of the Ce (III)/Ce (IV) redox couple inside, MVCM could directly catalyze the oxidation of 3,3 & PRIME;,5,5 & PRIME;-tetramethylbenzidine (TMB) to generate a blue color product (ox TMB) without adding H2O2, exhibiting a prominent intrinsic oxidase mimetic activity compared to Ce-MOF. Moreover, this catalytic mechanism of MVCM was further clarified by means of cyclic voltammetry (CV) test, UV-vis absorption spectra with O-2 or N-2 saturated condition and electron paramagnetic resonance (EPR) measurements. In the presence of AA, a redox reaction occurred between AA and ox TMB, and then resulting in a conspicuous blue color fading. By optimizing the testing conditions, a linear absorbance response was well correlated with the AA concentration ranging from 20 to 500 mu M with a detection limit of 3.57 mu M. MVCM also displayed the excellent selectivity and anti-interference performance for AA detection. Benefitting from the above, this AA detection method was applied in real Vitamin C effervescent tablets, showing a favorable reproducibility and feasibility. These results strongly indicated that the proposed method based on MVCM as an oxidase mimic might be a promising candidate for AA detection in food field.