A simple and rapid differential pulse voltammetric (DPV) method using a single-use electroactivated pencil graphite electrode (PGE*) is proposed for the rapid screening of the total content of polyphenolics (TCP) with intermediate antioxidant power (AOP) in grapefruit peel and fresh juice. The results were compared and correlated with those provided by the HPLC-DAD-MS method. NG voltammetric behavior at PGE* was studied by cyclic voltammetry and an oxidation mechanism was suggested. The experimental conditions (type of PGE, electroactivation procedure, pH, nature and concentration of supporting electrolyte) for NG DPV determination were optimized. The NG peak current varied linearly with the concentration in the ranges 1.40 × 10-6-2.00 × 10-5 and 2.00 × 10-5-1.40 × 10-4 mol/L NG and a limit of detection (LoD) of 6.02 × 10-7 mol/L NG was attained. The method repeatability expressed as relative standard deviation was 7.62% for the concentration level of 2.00 × 10-6 mol/L NG. After accumulation for 240 s of NG at PGE* the LoD was lowered to 1.35 × 10-7 mol/L NG, the linear range being 6.00 × 10-7-8.00 × 10-6 mol/L NG. The developed electrochemical system was successfully tested on real samples and proved to be a cost-effective tool for the simple estimation of the TCP with intermediate AOP in citrus fruits.
Keywords: disposable; electroactivated electrode; grapefruit; intermediate antioxidant power; naringin; pencil graphite electrode; total content of polyphenolics.