Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

Addressing the surface coverage of Au nano-agglomerates and the electrochemical properties of modified carbon paste electrodes: Experimental and theoretical studies on ascorbic acid oxidation

This article shows the formation of Au nano-agglomerates when increasing amounts of gold nanoparticles (AuNP) are incorporated into carbon paste electrodes. The surface coverage by this agglomerates is related to the electro-oxidation of a widely studied redox compound, ascorbic acid (AA); by analyzing the effect on the oxidation peak potential (E_p,a) and oxidation peak current (i_p,a). The effects of pH and scan rate on the E_p,a and i_p,_a were investigated by cyclic voltammetry, and enabled to estimate the transfer coefficient and the number of electrons involved in the rate determining step (αn_α), the standard heterogeneous rate constant (k_s), and the diffusion coefficient of the redox compound, being 0.52 and 3.5 × 10^-3 cm s^-1 and 6.3 × 10^-6 cm² s^-1, respectively. On the other hand, the sensing ability of the modified electrode was evaluated, obtaining a sensitivity of (63.2 ± 2.5) μA mM^-1, a detection limit of 2.7 μM and a quantification limit of 8.9 μM. Additionally, a computational model based on lattice-gas model and Monte Carlo simulations in the Grand Canonical Ensemble was proposed in order to reproduce the behavior of the system, in terms of i_p,a and E_p,a shift with increasing surface coverage by Au nano-agglomerates.

Sucrose Promotes Strawberry Fruit Ripening and Affects Ripening-Related Processes

Strawberry is a typical nonclimacteric fruit, whose ripening mechanism needs to be further investigated. Sucrose has been recently proved as a signal molecule, participating in strawberry fruit ripening and related processes. While in the effects of sucrose application timing and concentration on ripening, fruit qualities remain unclear, as well as the transcriptome-wide details about the effects of sucrose on the gene expression involved in ripening-related processes. In this study, strawberry fruits at the degreening (DG), white (W), and initial-red (IR) stages were treated with different concentration of sucrose. The results showed that anthocyanin was increased while total polyphenol concentration (TPC) and total flavonoid concentration (TFC) were decreased during fruit development after sucrose treatment. Interestingly, It was showed that 100 mM sucrose application at the DG stage had the most obvious effects on fruit ripening; it made all the fruits turn into full-red (FR) around 4 days (d) earlier than the control, while it did not affect fruit quality traits and most bioactive compounds in the FR fruits. Subsequently, RNA sequencing (RNAseq) of the fruits collected at 8 days after 100 mM sucrose treatment was carried out. It was suggested that 993 genes were differentially expressed comparing with the control. Transcriptome-based expression analysis revealed that sucrose induced the expression of genes involved in the AsA and anthocyanin biosynthesis, while largely suppressed the expression of genes in TCA. The results obtained in this study provided more expression profiles of ripening-related genes under the treatment of sucrose, which will contribute to a better understanding for the mechanism underlying sucrose-induced fruit ripening.

Sandwich-structured nanoparticles-grafted functionalized graphene based 3D nanocomposites for high-performance biosensors to detect ascorbic acid biomolecule

We present a highly sensitive and selective nano-biosensor for rapid, stable and highly reproducible detection of ascorbic acid (AA) in the presence of dopamine, uric acid and other interferences by a three-layer sandwich arrangement of nitrogen-doped functionalized graphene (NFG), silver nanoparticles (AgNPs) and nanostructured polyaniline (PANI) nanocomposite. The enhanced AA electrochemical properties of the NFG/AgNPs/PANI electrode is attributed to the superior conductivity of the NFG-PANI and the excellent catalytic activity of AgNPs. The critical modification of the AgNPs-grafted NFG-PANI coated on very low-cost fluorine doped tin oxide electrode (FTOE) increased the charge transfer conductivity of the electrode (the resistance drops down from 11,000 Ω to 6 Ω). The nano-biosensor was used to accurately detect AA in vitamin C tablets with the recovery of 98%. The sensor demonstrated a low detection limit of 8 µM (S/N = 3) with a very wide linear detection range of 10–11,460 µM, good reproducibility and excellent selectivity performance for AA detection. The results demonstrate that this nanocomposite is a promising candidate for rapid and selective detection of AA in practical clinical samples.

Fabrication of a Urea Biosensor for Real-Time Dynamic Fluid Measurement

In this study, a portable urea sensor that monitors the urea concentration in flow conditions was fabricated. We propose an electrochemical sensor that continually measures the urea concentration of samples flowing through it at a constant flow rate in real time. For the electrochemical sensing, a porous silk fibroin membrane with immobilized urease was mounted in a polydimethylsiloxane (PDMS) sensor housing. The fabricated urea sensor elicited linear current–concentration characteristics in the clinically significant concentration range (0.1–20 mM) based on peritoneal dialysis. The sensor maintained the linear current–concentration characteristics during operation in flow conditions.

Simultaneous determination of ascorbic acid and caffeine in commercial soft drinks using reversed-phase ultraperformance liquid chromatography

A new reversed-phase ultraperformance liquid chromatography method with a photodiode array detector was developed for the quantification of ascorbic acid (AA) and caffeine (CAF) in 11 different commercial drinks consisting of one energy drink and 10 ice tea drinks. Separation of the analyzed AA and CAF with an internal standard, caffeic acid, was performed on a Waters BEH C₁₈ column (100 mm × 2.1 mm, 1.7 μm i.d.), using a mobile phase consisting of acetonitrile and 0.2M H₃PO₄ (11:89, v/v) with a flow rate of 0.25 mL/min and an injection volume of 1.0 μL. Calibration graphs for AA and CAF were computed from the peak area ratio of AA/internal standard and CAF/internal standard detected at 244.0 nm and 273.6 nm, respectively. The developed reversed-phase ultraperformance liquid chromatography method was validated by analyzing standard addition samples. The proposed reversed-phase ultraperformance liquid chromatography method gave us successful results for the quantitative analysis of commercial drinks containing AA and CAF substances.

Application of novel Ni(II) complex and ZrO2 nanoparticle as mediators for electrocatalytic determination of N-acetylcysteine in drug samples

The electrooxidation of N-acetylcysteine (N-AC) was studied by a novel Ni(II) complex modified ZrO₂ nanoparticle carbon paste electrode [Ni(II)/ZrO₂/NPs/CPE] using voltammetric methods. The results showed that Ni(II)/ZrO₂/NPs/CPE had high electrocatalytic activity for the electrooxidation of N-AC in aqueous buffer solution (pH = 7.0). The electrocatalytic oxidation peak currents increase linearly with N-AC concentrations over the concentration ranges of 0.05-600μM using square wave voltammetric methods. The detection limit for N-AC was equal to 0.009μM. The catalytic reaction rate constant, k_h, was calculated (7.01 × 10² M^-1 s^-1) using the chronoamperometry method. Finally, Ni(II)/ZrO₂/NPs/CPE was also examined as an ultrasensitive electrochemical sensor for the determination of N-AC in real samples such as tablet and urine.

Fabrication of a heated electrode modified with a thiol-functionalized ionic liquid for electrochemical/electrochemiluminescence sensors

A new heated thiol-functionalized ionic liquid (TFIL)/Au composite electrode, which possessed the advantages of a heated electrode technique and ionic liquids (ILs), was designed and fabricated in this study.

Nickel oxide nanoparticles/ionic liquid crystal modified carbon composite electrode for determination of neurotransmitters and paracetamol

Ionic liquid crystals mimic the natural bio-based ionic liquid crystals such as cell membrane structures in their interactions with drugs.

Microelectrodes based on porphyrins for the determination of ascorbic acid in pharmaceutical samples and beverages

Different porphyrins were used for the design of seven carbon paste and seven diamond paste based microelectrodes, which were employed for the determination of ascorbic acid in pharmaceutical and beverages samples using differential pulse voltammetry (DPV). The limits of detection lie between 1.1 × 10-14 and 5.1 × 10-7 M while the sensitivities were between 3.07 pA/M and 1285.18 A/M. Ascorbic acid was recovered reliable from pharmaceutical and beverages samples in percentages higher than 92.00% and 91.50%, respectively. The surface of the microelectrodes can easily be renewed by simple polishing, obtaining a fresh surface ready for use in a new assay.

Electrochemical behavior and determination of rutin on modified carbon paste electrodes

The performances of ionic liquid (1-hexyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide, IL/CPE) and iron phthalocyanine (IP/CPE) modified carbon paste electrodes in electroanalytical determinations of rutin were evaluated and compared to the performance of unmodified carbon paste electrode (CPE). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), differential pulse adsorptive stripping voltammetry (DPAdSV), and amperometry were used for rutin analysis. The best current responses of rutin were obtained at pH 4.0 for all tested techniques. IL/CPE electrode was found to perform best with DPAdSV technique, where a detection limit (LOD) as low as 5 nmol L⁻¹ of rutin was found. On the other hand, IP/CPE showed itself to be an optimum choice for DPV technique, where LOD of 80 nmol L⁻¹ was obtained. Analytical applicability of newly prepared electrodes was demonstrated on determination of rutin in the model samples and the extracts of buckwheat seeds. To find an optimum method for buckwheat seeds extraction, a boiling water extraction (BWE), Soxhlet extraction (SE), pressurized solvent extraction (PSE), and supercritical fluid extraction (SFE) were tested.

Carbon paste electrodes in the new millennium

In this review (with 500 refs), both electrochemistry and electroanalysis with carbon paste-based electrodes, sensors, and detectors are of interest, when attention is focused on the research activities in the years of new millennium. Concerned are all important aspects of the field, from fundamental investigations with carbon paste as the electrode material, via laboratory examination of the first electrode prototypes, basic and advanced studies of various electrode processes and other phenomena, up to practical applications to the determination of inorganic ions, complexes, and molecules. The latter is presented in a series of extensive tables, offering a nearly complete survey of methods published within the period of 2001–2008. Finally, the latest trends and outstanding achievements are also outlined and future prospects given.