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The determination of antioxidant capacity, total phenolics, and ascorbic acid using accurate, efficient, low cost, and rapid methods has great analytical importance. The antioxidant capacity, total phenolics, and ascorbic acid content of apricots, arugula, banana, cranberries, spinach, and strawberries were investigated with an electrochemical approach and examined for compatibility with conventional methods. The antioxidant activity was determined by ABTS and DPPH assays. The total phenolic content was determined by the Folin Ciocalteu method and ascorbic acid was quantified by high-performance liquid chromatography (HPLC). In order to perform sensitive and simultaneous electrochemical measurements, the surface of a glassy carbon electrode (GCE) was modified by electropolymerization with p-toluene sulfonic acid (TSA). The TSA/GCE modified sensor was used for the first time for the determination of antioxidant capacity and total phenolic content. The surface of the modified sensor was characterized by cyclic voltammetry and scanning electron microscopy. The TSA/GCE was linearly correlated with the differential pulse voltammetry (DPV) for Trolox and gallic acid in 0.1 M NaNO3 and ascorbic acid in pH 7.4 phosphate buffer. Electrochemical methods offer a promising alternative for the determination of antioxidant capacity and total phenolic content due to their simplicity, rapid response, low cost, sensitivity, and reproducibility. [ABSTRACT FROM AUTHOR]

This work presents a simple, low cost, and portable spectrophotometer based on a digital microscope as a detector for the determination of the antioxidant activity and total phenolic content (TPC). The antioxidant activity was expressed as ascorbic acid equivalents (AAE) using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay. The TPC value was measured using the Folin-Ciocalteu method. The color of the products was captured using a digital microscope powered through the USB output of a laptop. A digital microscope, held in a 3D printing device was used to take photos of the reaction product that was illuminated with the stable light source of the digital microscope. The pictures were analyzed for quantitation. For the DPPH assay, the developed method provided a working range from 0.6 to 6 mg L−1 of ascorbic acid with a limit of detection (LOD) of 0.2 mg L−1 and a relative standard deviation (RSD) of 2.2%. The TPC method provided a working range from 4.6 to 100 mg L−1 for gallic acid, with a LOD of 1.4 mg L−1 and a RSD of 1.3%. Results of the proposed system agree well with a conventional spectrophotometric method and have been successfully applied to measure the antioxidant activity and TPC of local Thai tea samples. [ABSTRACT FROM AUTHOR]