An Electrode Based on Manganese Dioxide Nanorods and Hexadecylpyridinium Bromide for the Rosmarinic Acid Voltammetric Assay

Abstract

Nanostructures of transition metal oxides have shown to be effective sensing layers of electrodes used in electroanalytical chemistry. Manganese dioxide nanorods (MnO2 NRs) are of interest and have been applied in colorant electroanalysis. An electrode modified with MnO2 NRs prepared in hexadecylpyridinium bromide (HDPB) medium is developed for rosmarinic acid quantification. The application of HDPB as a dispersive agent provides stabilization of nanomaterial suspension in a water medium. The developed electrode gives an improved response to rosmarinic acid, i.e., 60 mV redox peak potential separation and 1.7-fold increased redox currents have been observed. Quasi-reversible electrooxidation controlled by surface processes has been confirmed. The analytical response of rosmarinic acid has been obtained by differential pulse voltammetry (DPV) in Britton–Robinson buffer (BRB) pH 5.0. The method makes possible rosmarinic acid determination from 2.5 × 10−8 to 1.0 × 10−6 M and from 1.0 × 10−6 to 1.0 × 10−5 M and provides a detection limit equal to 9.7 × 10−9 M. These characteristics are improved vs. reported electrochemical approaches. The selectivity of the electrode response to rosmarinic acid is shown using a 1000-fold excess of inorganic ions, 100-fold excesses of saccharides, and 10-fold excesses of ascorbic and p-coumaric acids, eugenol, carvacrol, and thymol. Other phenolic acids (gallic, ferulic, caffeic) and flavonoids (quercetin, rutin) give an interference effect. Rosemary spices have been studied to prove the practical applicability of the MnO2 NRs-based electrode.

Keywords

• modified electrodes
• voltammetry
• metal oxide nanomaterials
• natural phenolics
• rosmarinic acid