Analysis of gentisic acid and related renal cell carcinoma biomarkers using reversed-phase liquid chromatography with water-rich mobile phases

Spectral and time domain fluorescence spectroscopy of gentisic acid molecule in protic and aprotic polymer matrix

In the present work, the effect of polymer microenvironment on the photophysics of gentisic acid molecule [2,5-dihydroxybenzoic acid] (GA), steady-state and time-domain fluorescence measurements at different pH conditions were carried out in protic [polyvinyl alcohol PVA] and aprotic [polymethyl methacrylate (PMMA)] polymer matrices. Change in the proticity of the microenvironment of the polymer traps different ionic species along with the neutral form of rotamer P and R conformers of GA molecule, are found to be responsible for the change in the spectral, multi-exponential decay behaviour. In protic polymer, the appearance of a single emission band indicates, dissociation of the GA molecule is very high, and it present as a monoanion along with hydrogen-bonded P and R rotamers. However, in the basic polymer film, most of the conformers of R converted to the anion. In contrast, protonation slows down the dissociation of both P and R forms in the acidic film. Unlike PVA matrix, in PMMA, dual emission band appears due to slow dissociation of GA molecule and hydrogen-bonded rotamer P, and R form exists with monoanion species. The magnitude of large stokes shifted red emission due to excited-state intramolecular proton transfers (ESIPT) found grater in rotamer P compared to its anionic species (green emission) and a blue emission corresponds to rotamer R.

A new sensor based on an amino-montmorillonite-modified inkjet-printed graphene electrode for the voltammetric determination of gentisic acid

An amperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH₂) for the electroanalysis and quantification of gentisic acid (GA) has been developed. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH₂/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high in acidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3 s^-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233 V vs. a pseudo Ag/Ag⁺ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21 μM (R² = 0.999), and a low detection limit of 0.33 μM (0.051 ± 0.01 mg L^-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developed using a cheap clay material could be employed for the determination of various phenolic acids.