Simultaneous Detection of Ascorbic Acid and Hydrogen Peroxide by Flow‐Injection Analysis with a Thin Layer Dual‐Electrode Detector

Abstract

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 (0.1 mm) 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 (0.3 V vs. Ag/AgCl,Cl À sat ), while H 2 O 2 alone can be oxidized at the Pt electrode (0.75 V), thanks to the size selectivity and electrostatic screen properties displayed by the polyeugenol coating layer which prevents oxidation of ascorbate anions. Repeatable sharp peaks (AE 4.5 %) were detected for both analytes over wide linear ranges (0.005-1.000 mM) and detection limits of about 10 À6 M (176 ppb) and 5 10 À7 M (16 ppb) were inferred for AA and H 2 O 2 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.

Pencil‐Drawn Dual Electrode Detectors to Discriminate Between Analytes Comigrating on Paper‐Based Fluidic Devices but Undergoing Electrochemical Processes with Different Reversibility

“…As to DA+AA samples, both compounds undergo at graphite electrodes a two‐electron two‐proton oxidation process at very near potentials, as shown in Figure 3 Inset, in agreement with literature reports 37–39. However, DA oxidation leads to o ‐dopaminoquinone (DAQ), whose reduction (renewing DA) occurs in the reverse scan at less positive potentials (of about 370 mV, under our experimental conditions), while dehydroascorbic acid formed by AA oxidation is not reduced within the potential window explored.…”

“…Also in this case, both analytes underwent electrochemical oxidation at near enough potentials, as shown in Figure 5 Inset. PA oxidation led to a product containing a quinone moiety which could be reduced (renewing PA) in the reverse scan, while an irreversible oxidation took place for AA 39, 41. Thin‐layer chromatographic runs were first conducted by applying once again 600 nL of sole PA or sole AA samples to the spot area (3 mm from W 1 ) and imposing potentials of 800 mV and −200 mV to W 1 and W 2 , respectively.…”

Pencil‐drawn paper supported electrodes as simple electrochemical detectors for paper‐based fluidic devices

“…As a matter of fact, such a shift was observed for sunset yellow in all the pH interval explored, while for ascorbic acid a peak shift was found only in the range 2–4.5. This finding was in full agreement with the fact that a pK a = 10.3 is proper for the phenol–OH group (oxidation site for the azo‐dye sunset yellow), while a pK a = 4.1 characterizes the first dissociation step of ascorbic acid .…”

MOF modified pencil electrode for hydrogen peroxide detections

“…H 2 O 2 is considered the most common reactive oxygen species (ROS) and byproduct of the oxidative metabolic pathway (Lu, Wen, and Li 2006). Simple and reliable hydrogen peroxide (H 2 O 2 ) measurements are needed in different fields in recent years, because of the important role of H 2 O 2 in chemicals production, fuel cells, biotechnology, environmental, pharmaceutical and clinical applications (Jia et al 2014;Reza and Bagheri 2014;Sawangphruk et al 2014;Tang, Yuan, and Chai 2006;Toniolo et al 2011).…”