Simultaneous detection of ascorbic acid and hydrogen peroxide by flow-injection analysis with a thin layer dual-electrode detector

Based on preliminary voltammetric investigations at unmodified and modified electrodes in aqueous solutions buffered at different pHs, a profitable thin layer dual-electrode detector was developed for the selective and simultaneous determination of ascorbic acid (AA) and hydrogen peroxide present in the same samples. It consists of a small thickness (0.1mm) cell, used as a detector for a flow injection system, in which a glassy carbon (GC) and a polyeugenol coated Pt electrode are encased. The GC electrode is selective for AA, thanks to the potential applied (0.3V vs. Ag/AgCl,Cl- sat), while H2O2 alone can be oxidized at the Pt electrode (0.75V), thanks to the size selectivity and electrostatic screen properties displayed by the polyeugenol coating layer which prevents oxidation of ascorbate anions. Repeatable sharp peaks (±4.5%) were detected for both analytes over wide linear ranges (0.005-1.000mM) and detection limits of about 10-6M (176ppb) and 5×10-7M (16ppb) were inferred for AA and H2O2 respectively. This flow injection approach was applied to the analysis of some orange-taste soft drinks, used as prototype real samples, spiked with controlled amounts of both analytes, thus inferring good recoveries which pointed out that deviations never exceeding 5% affected the relevant accuracy.