A new electrochemical sensor for simultaneous determination of arbutin and vitamin C based on hydroxyapatite-ZnO-Pd nanoparticles modified carbon paste electrode.

A highly sensitive and selective sensor was fabricated based on Hydroxyapatite-ZnO-Pd NPs modified carbon paste electrode (HAP- ZnO-Pd NPs/CPE) for simultaneous determination of Arbutin (AT) and vitamin C (VC) for the first time. Characterization was performed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The modified electrode was studied by different methods including electrochemical impedance spectroscopy and cyclic voltammetry. The HAP- ZnO-Pd NPs/CPE exhibited excellent electrocatalytic activity towards the oxidations of AT and VC in phosphate buffer solution (pH 7.0) and the corresponding electrochemical signals have appeared as two well resolved oxidation peaks with significant peak potential differences of 0.23 V. Kinetic parameters such as charge transfer coefficient (0.52 and 0.44 for AT and VC respectively), standard heterogeneous electron transfer rate constant (0.336 s-1 and 0.590 s-1 for AT and VC respectively), and other electrochemical parameters were calculated via voltammetry techniques. Differential pulse voltammetry was used for simultaneous determination of AT and VC using the HAP- ZnO-Pd NPs/CPE electrode. At the optimum conditions, for simultaneous determination by synchronous change of the analyte concentrations, the linear response ranges were between 0.12-56 µM for AT and 0.12-55.36 µM for VC with detection limits of 85.7 and 19.4 nM respectively while sensitivity of proposed sensor for AT and VC was 0.98 µA/µM and 0.94 µA/µM. Reproducibility (intra-; 1.16% and 1.16% for AT and VC respectively and inter-electrode reproducibility of 2.03% and 3.28 for AT and VC respectively), and response time about 3.5 min were obtained. Furthermore, HAP- ZnO-Pd NPs/CPE was successfully applied for the independent determination of VC in fruit juice as well as the simultaneous determination of AT and VC in lightening cream samples.

A simple ultrasensitive electrochemical sensor for simultaneous determination of gallic acid and uric acid in human urine and fruit juices based on zirconia-choline chloride-gold nanoparticles-modified carbon paste electrode.

The determination of gallic acid (GA) and uric acid (UA) is essential due to their biological properties. Numerous methods have been reported for the analysis of GA and UA in various real samples. However, the development of a simple, rapid and practical sensor still remains a great challenge. Here, a carbon paste electrode (CPE) was modified by nanocomposite containing zirconia nanoparticles (ZrO2NPs), Choline chloride (ChCl) and gold nanoparticles (AuNPs) to construct ZrO2-ChCl-AuNPs/CPE as electrochemical sensor for the simultaneous electro-oxidation of GA and UA. Characterization was performed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The modified electrode was investigated by different methods including electrochemical impedance spectroscopy and cyclic voltammetry. Kinetic parameters such as charge transfer coefficient, standard heterogeneous electron transfer rate constant and other parameters were calculated via voltammetry techniques. Differential pulse voltammetry was used for simultaneous determination of GA and UA applying the ZrO2-ChCl-AuNPs/CPE electrode. At the optimum conditions, this sensor showed a linear response in the ranges 0.22- 55 and 0.12-55 µM for GA and UA, respectively. In addition, low detection limits of 25 and 15 nM were obtained for GA and UA, respectively. Furthermore, ZrO2-ChCl-AuNPs/CPE was successfully applied for the independent determination of GA in green tea and fruit juice as well as the simultaneous determination of GA and UA in human urine samples.

Design a sensitive optical thin film sensor based on incorporation of isonicotinohydrazide derivative in sol-gel matrix for determination of trace amounts of copper (II) in fruit juice: Effect of sonication time on immobilization approach.

A new selective and sensitive optical sensor based on the incorporation of new synthesized N'-(2-hydroxy-5-iodobenzylidene) isonicotinohydrazide (HIBIN) as an effective reagent into the nanoporous of a transparent glass like material through the sol-gel process was developed which was suitable for the determination of copper (II) ions in aqueous solutions. The thin film sensors were constructed by spin-coating of prepared sol onto glass plate and their surface morphology were studied by field emission scanning electron microscopy (FE-SEM) and atomic force microscope (AFM) technique. Influence of sonication time on immobilization of HIBIN into silica matrix was investigated through calculation of leaching percentage. The Results shown that sonication time of 35 min is suitable to give more stable thin films without fluctuation in sensitivity and response time of presented sensor for a long period of time. The proposed optical sensor can be used for determination of copper (II) ions in the range of 9.1 × 10-8-1.12 × 10-5 mol L-1with a detection limit of 1.8 × 10-8 mol L-1. It also showed relative standard deviation 3.4 and 0.72% for reproducibility and repeatability respectively, along with a fast response time about of 2 min. The constructed optode is stable in wet conditions and could be stored for at least 6 weeks without observing any change in its sensitivity. The developed sensor was successfully applied to the determination of copper (II) in fruit juice and water samples which results were confirmed by atomic absorption spectrometry method.