Voltammetric detection of synthetic water-soluble phenolic antioxidants using carbon nanotube based electrodes

Fabrication of CeO2/GCE for Electrochemical Sensing of Hydroquinone

Hydroquinone is a widely used derivative of phenol which has a negative influence on human beings and the environment. The determination of the accurate amount of hydroquinone is of great importance. Recently, the fabrication of an electrochemical sensing device has received enormous attention. In this study, we reported on the facile synthesis of cerium dioxide (CeO₂) nanoparticles (NPs). The CeO₂ NPs were synthesized using cerium nitrate hexahydrate as a precursor. For determining the physicochemical properties of synthesized CeO₂ NPs, various advanced techniques, viz., powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), were studied. Further, these synthesized CeO₂ NPs were used for the modification of a glassy carbon electrode (CeO₂/GCE), which was utilized for the sensing of hydroquinone (HQ). A decent detection limit of 0.9 µM with a sensitivity of 0.41 µA/µM cm² was exhibited by the modified electrode (CeO₂/GCE). The CeO₂/GCE also exhibited good stability, selectivity, and repeatability towards the determination of HQ.

Sensitive voltammetric quantification of carminic acid in candies using selenium dioxide nanoparticles based electrode

Carminic acid is a food colorant which concentration has to be controlled due to the possible negative health effects. Sensitive voltammetric method is developed for carminic acid determination using electrode modified with SeO₂ nanoparticles (SeO₂ NPs) and hexadecyltriphenylphosphonium bromide (HDTPPB) acting as dispersive agent for nanoparticles and electrode surface co-modifier. SeO₂ NPs of 37-45 nm are uniformly distributed at the electrode increasing its electroactive area (41 ± 2 vs. 8.9 ± 0.2 mm² for bare glassy carbon electrode (GCE)). Electrochemical impedance spectroscopy data confirm an 18.3-fold decrease of charge transfer resistance compared to GCE (12.7 ± 0.3 vs. 232 ± 7 kΩ, respectively). In differential pulse mode, the linear dynamic ranges of carminic acid are 0.010-2.5 and 2.5-10 μmol L^-1 with a detection limit of 3.4 nmol L^-1. The method is successfully employed in candies and lozenges for sore throat treatment. The approach is simple, reliable, and can be used as an alternative to chromatography in routine analysis.

Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity

Carbon nanomaterials have gained significant interest over recent years in the field of electrochemistry, and they may be limited in their use due to issues with their difficulty in dispersion. Enzymes are prime components for detecting biological molecules and enabling electrochemical interactions, but they may also enhance multiwalled carbon nanotube (MWCNT) dispersion. This study evaluated a MWCNT and diamine oxidase enzyme (DAO)-functionalised screen-printed electrode (SPE) to demonstrate improved methods of MWCNT functionalisation and dispersion. MWCNT morphology and dispersion was determined using UV-Vis spectroscopy (UV-Vis) and scanning electron microscopy (SEM). Carboxyl groups were introduced onto the MWCNT surfaces using acid etching. MWCNT functionalisation was carried out using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), followed by DAO conjugation and glutaraldehyde (GA) crosslinking. Modified C-MWNCT/EDC-NHS/DAO/GA was drop cast onto SPEs. Modified and unmodified electrodes after MWCNT functionalisation were characterised using optical profilometry (roughness), water contact angle measurements (wettability), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) (vibrational modes and elemental composition, respectively). The results demonstrated that the addition of the DAO improved MWCNT homogenous dispersion and the solution demonstrated enhanced stability which remained over two days. Drop casting of C-MWCNT/EDC-NHS/DAO/GA onto carbon screen-printed electrodes increased the surface roughness and wettability. UV-Vis, SEM, Raman and EDX analysis determined the presence of carboxylated MWCNT variants from their non-carboxylated counterparts. Electrochemical analysis demonstrated an efficient electron transfer rate process and a diffusion-controlled redox process. The modification of such electrodes may be utilised for the development of biosensors which could be utilised to support a range of healthcare related fields.

Chronocoulometry of wine on multi-walled carbon nanotube modified electrode: Antioxidant capacity assay

Phenolic antioxidants of wine were electrochemically oxidized on multi-walled carbon nanotubes modified glassy carbon electrode (MWNT/GCE) in phosphate buffer solution. Three oxidation peaks were observed at 0.39, 0.61 and 0.83V for red dry wine and 0.39, 0.80 and 1.18 V for white dry wine, respectively, using differential pulse voltammetry at pH 4.0. The oxidation potentials for individual phenolic antioxidants confirmed the integral nature of the analytical signals for the wines examined. A one-step chronocoulometric method at 0.83 and 1.18 V for red and white wines, respectively, has been developed for the evaluation of wine antioxidant capacity (AOC). The AOC is expressed in gallic acid equivalents per 1L of wine. The AOC of white wine was significantly less than red wine (386 ± 112 vs. 1224 ± 184, p<0.0001), as might be expected. Positive correlations were observed between gallic acid equivalent AOC of wine and total antioxidant capacity, based on coulometric titration with electrogenerated bromine (r=0.8957 at n=5 and r=0.8986 at n=4 for red and white wines, respectively).

The electrochemical catalytic behavior of pyrogallol at an 8-hydroxyquinoline-aluminum complex modified carbon paste electrode and its detection in tomato

Tomato (Solanum lycopersicum) fruit is an excellent food for promoting human health and wellbeing due to its containing polyphenols as antioxidants.

A quantum chemical study on the electrochemical behaviour and solid phase microextraction of pyrogallol at an aluminum-8-hydroxylquinonoline modified carbon paste electrode

Quantum chemistry calculation was performed with PM6 in MOPAC2012 software based on the molecular cluster models of a piece of graphene including 38 carbon atoms, 8-hydroxylquinoline-alumium complexes and pyrogallol in vacuum conditions.

Cyclic voltammetry of natural flavonoids on MWNT-modified electrode and their determination in pharmaceuticals

The determination of rutin, quercetin and taxifolin in pharmaceutical dosage forms using cyclic voltammetry on multi-walled carbon nanotube modified glassy carbon electrode (MWNT-GCE) has been developed. The surface of the electrode created has been characterized by atomic force microscopy. Electrode modification with MWNT increases the surface average roughness (190-fold) and structures it. There are two oxidation steps at 0.22 and 0.80, 0.23 and 0.80, 0.26 and 0.86 V on cyclic voltammograms of taxifolin, quercetin and rutin, respectively, in phosphate buffer solution of pH 7.4. The linear dynamic range is 1.4–28 and 28–210, 2.0–220 and 0.52–210 μM with detection limits of 0.71, 1.0 and 0.26 μM for rutin, quercetin and taxifolin, respectively. The relative standard deviation of flavonoids determination in pharmaceuticals does not exceed of 7%. The data obtained are in good agreement with coulometric determination.