The electrochemical determination of ascorbic acid was carried out at the surface of glassy carbon electrode (GCE) modified by silver nanoparticles (AgNPs):Polyvinylpyrrolidone (PVP). Nanocomposite was evaluated by fourier transform infrared spectroscopy, zeta potential, and X‐ray diffraction. Also, the surface morphologies of the developed electrode were investigated by scanning electron microscopy, and profilometer. The electrochemical performance of AgNPs/PVP/GCE was studied with cyclic voltammetry and electrochemical impedance spectroscopy measurements. The electrochemical studies demonstrated that the electrode had a large surface. Compared with the bare GCE, PVP/GCE, and AgNPs/GCE, the AgNPs/PVP‐modified GCE showed excellent performance for the electrochemical determination of ascorbic acid. At the optimized conditions of differential pulse voltammetry in pH 6.0 of phosphate buffer solution, the modified electrode allowed the determination of ascorbic acid on a potential of 0.54 V vs. Ag/AgCl. Under optimized conditions, the low detection limit of 0.047 μM and working range of 0.2‐1200 μM were obtained at the AgNPs/PVP/GCE. The AgNPs/PVP/GCE allowed to obtain highest peak current values at low concentrations. Moreover, the fabricated electrode also exhibited good repeatability, reproducibility, and stability. The developed electrode was successfully enforced for the analysis of ascorbic acid in banana, kiwi fruit, mango, and pineapple.

This paper describes an electroanalytical method for the determination of rapamycin using a pretreated pencil graphite electrode (P‐PGE) by differential pulse voltammetry. The electrodes were successfully characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and Fourier transform infrared. The influences of instrumental and chemical parameters were investigated and optimized for the determination of rapamycin. Oxidation peak current obtained for rapamycin at P‐PGE was 10.5 times higher than that obtained for PGE. In pH = 3.0 H3PO4, a well‐defined irreversible anodic peak occurred at 1.07 V, which was attributed to the electro‐oxidation of rapamycin at P‐PGE. Under optimized conditions, the oxidation peak current of rapamycin was linear with its concentration in the range of 0.01–250 μmol/L, and the detection limit was 0.0075 μmol/L (S/N = 3). Also, the P‐PGE exhibited good reproducibility (relative SD [RSD] = 2.17% for 10 electrodes at different times using the same procedure), repeatability (RSD = 2.09% for 10 measurements with same electrode), and stability (95.80% for 10 days). The P‐PGE was simple to prepare and the method was successfully applied for the determination of rapamycin in spiked and real samples. In addition, for comparison, high‐performance liquid chromatographic method with ultraviolet (UV) detector was used for the determination of rapamycin.

In the present study, interactions of Au(III) and Ga(III) ions on human serum albumin (HSA) were studied comparatively via spectroscopic and thermal analysis methods: UV-vis absorbance spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and isothermal titration calorimetry (ITC). The potential antitumor effects of these ions were studied on MCF-7 cells via Alamar blue assay. It was found that both Au(III) and Ga(III) ions can interact with HSA, however; Au(III) ions interact with HSA more favorably and with a higher affinity. FT-IR second derivative analysis results demonstrated that, high concentrations of both metal ions led to a considerable decrease in the α-helix content of HSA; while Au(III) led to around 5% of decrease in the α-helix content at 200μM, it was around 1% for Ga(III) at the same concentration. Calorimetric analysis gave the binding kinetics of metal-HSA interactions; while the binding affinity (Ka) of Au(III)-HSA binding was around 3.87×10(5)M(-1), it was around 9.68×10(3)M(-1) for Ga(III)-HSA binding. Spectroscopy studies overall suggest that both metal ions have significant effects on the chemical structure of HSA, including the secondary structure alterations. Antitumor activity studies on MCF7 tumor cell line with both metal ions revealed that, Au(III) ions have a higher antiproliferative activity compared to Ga(III) ions.

The chemical structures of quercetin and luteolin are quite similar; as a result, their oxidation peaks potential are close and interfere each other. To solve this problem, in this study, the simultaneous determination method of quercetin and luteolin has been developed on glassy carbon electrode (GCE) by using differential pulse voltammetry (DPV). 75% methanol (hydro-alcoholic) support electrolyte was used for this purpose. The peak potential difference between the quercetin and luteolin was at about 110 mV which was useful for the simultaneous electrochemical analysis of both species. The experimental parameters were optimized. Under optimized conditions, linearity was obtained in the ranges of 0.079-39.60 × 10-7 M and 39.60-148.50 × 10-7 M for quercetin, and 0.065-32.60 × 10-7 M and 32.60-122.50 × 10-7 for luteolin. The detection limits for quercetin and luteolin were 0.022 × 10-7 M and 0.018 × 10-7 M, respectively. Finally, the present method was employed for the simultaneous determination of quercetin and luteolin in the ethanol and methanol extracts of Mate and White tea samples, and the obtained results were verified by high performance liquid chromatography as a confirmatory method.

SUMMARY In this work, we developed a sensitive, simple and convenient electrochemical method to determine Sudan 1 in food samples using its Cu(II) coordination compound. Using phosphate buffer solution at pH=5.0 as supporting electrolyte (75% methanol), differential pulse voltammetry and 6-fold concentration of Cu(II), the electrochemical oxidation signal of Sudan 1–Cu(II) coordination compound at glassy carbon electrode significantly increased when compared to the one without the added Cu(II). The experimental conditions such as the amount of methanol, pH, the concentration of Cu(II) and the instrumental parameter were optimized for the determination of Sudan 1. Under the optimal experimental conditions, the oxidation peak current of Sudan 1 was proportional to its concentration in two ranges: 0.04–0.09 to 0.09–5.3 µM with a detection limit of 0.71 nM ( S / N =3). The interference effects of Sudan 2-4 with the determination of Sudan 1 was also evaluated. The developed method was successfully applied to tomato, chilli sauces, ketchup and chilli powder. The analysis results of Sudan 1 in food samples obtained by the proposed method were in a good agreement with the reference values detected by HPLC.