Utilizing epicatechin voltammetric oxidation signal for the estimation of total phenolic content in the tea samples via the unmodified boron-doped diamond electrode surface

Abstract

In this work, the boron-doped diamond (BDD) electrode surface was employed for the first time in conjunction with the epicatechin (EC) oxidation signal to estimate the total phenolic content of tea samples by voltammetry. During cyclic voltammetry analysis of the EC, an easily identifiable, irreversible, and adsorption-controlled oxidation peak was observed at around +1.05 V (vs. Ag/AgCl) in HNO3 solution. Our experimental setup was fine-tuned by investigating the effect of electrode pretreatment, pH of the supporting electrolyte, accumulation factors, and instrumental parameters on the oxidation peak response of EC. When measuring EC in a 0.1 mol L−1 HNO3 solution at +1.0 V, square-wave adsorptive stripping voltammetry provided a highly linear response (at open-circuit accumulation for 30 s). The dynamic range was determined to be between 1.0 and 50.0 μg mL−1 (3.4510−6–1.7210−4 mol L−1), while the detection limit was found to be 0.28 μg mL−1 (9.6510−7 mol L−1). Selectivity studies were performed with other phenolic compounds found in tea such as epigallocatechin gallate, catechin, tannic acid, and gallic acid. Finally, by assessing the total phenolic content in the black and green tea samples, the suggested approach's applicability was shown by providing an estimate of the EC equivalents present in the samples.