Determination of catalytic oxidation products of phenol by RP-HPLC

Tb-based Metal-Organic Framework-Referenced Fluorescence Assay for Distinguishing Hydroquinone from Its Isomers and Subsequent Quantitative Visual Detection of Cu2

Hydroquinone (HQ) and copper ions (Cu2+) are categorized as environmental pollutants that are severely limited in water. Designing a selective assay for discriminating HQ from its two isomers and the convenient determination of Cu2+ is of great importance. Herein, a Tb-based metal-organic framework (Tb-MOF) and HQ are assembled innovatively into a ratiometric fluorescence nanoprobe to selectively distinguish HQ and subsequent quantitative visual detection of Cu2+. The native blue emission of HQ at 338 nm is used as a response signal, while Tb-MOF with green fluorescence offers a reference signal at 545 nm. Notably, neither resorcinol (RC) nor catechol (CC) exhibits obvious emission under the same experimental conditions, which enables discriminating HQ from its isomers. Thus, a ratiometric fluorescence method has been designed for the selective detection of HQ with the fluorescence intensity ratio F338/F545 as the readout. The redox reaction between HQ and Cu2+ induces fluorescence quenching of HQ and no change to that of Tb-MOF, resulting in a noticeable color variation from blue-green to green via the naked eye. Furthermore, sensitive visual detection of Cu2+ is achieved with a low detection limit of 1.67 μM using a smartphone. The satisfactory recoveries and good repeatability of quantitative visualization determined in spiked water samples make this sensing platform suitable for on-site monitoring of environmental samples.

A new amperometric biosensor based on Fe3O4/polyaniline/laccase/chitosan biocomposite-modified carbon paste electrode for determination of catechol in tea leaves

In the present study, a new biosensor based on laccase from Paraconiothyrium variabile was developed for catechol. The purified enzyme entrapped into the Fe3O4/polyaniline/chitosan (Fe3O4/polyaniline (PANI)/chitosan (CS)) biocomposite matrix film without the aid of other cross-linking reagents by a one-step electrodeposition on the surface of carbon paste electrode (CPE). The formed layer of biocomposite was characterized with scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The biosensor was optimized with respect to biocomposite composition, enzyme loading, and solution pH by amperometry method. The biosensor exhibited noticeable eletrocatalytic ability toward catechol with a linear concentration range from 0.5 to 80 μM and a detection limit of 0.4 μM. The biosensor showed optimum response within 8 s, at pH 5, and 40 °C. The apparent Michaelis-Menten (K M (app)) was found to be 1.092 μM. The fabricated biosensor could be applied for determination of catechol in tea leaf samples.