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A voltammetric sensor was fabricated by applying a Nafion and multi-walled carbon nanotubes (MWCNTs) composite film on the surface of a carbon ionic liquid electrode (CILE), which was prepared by mixing 1-butyl-3-methylimidazolium hexafluorophosphate with graphite powder. The electrochemical behavior of adenine on the Nafion-MWCNTs/CILE was investigated in pH 5.5 buffer solution. Adenine showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response, which was due to the presence of high conductive MWCNTs on the CILE surface. The electrochemical parameters of adenine electro-oxidation were determined, and the experimental conditions were optimized. Under the optimal conditions, the oxidation peak current was linear to the adenine concentration over the range of 1.0 × 10−7 to 7.0 × 10−5 mol L−1 with a detection limit of 3.3 × 10−8 mol L−1 (signal/noise = 3). The electrode showed good stability and selectivity, and was further applied to milk powder samples with satisfactory results. [ABSTRACT FROM AUTHOR]

An electrode modified with an ionic liquid was used for the electrochemical determination of 3,4-dihydroxybenzoic acid (DHBA). Cyclic voltammetry indicated a pair of well-defined quasi-reversible redox peaks with a formal peak potential located at 586 mV (vs. the SCE). The voltammetric response to DHBA is largely improved compared to a traditional carbon paste electrode. This is attributed to a larger interface (due to the presence of an ionic liquid) with higher conductivity and inherent catalytic capability. The charge transfer coefficient, the standard rate constant and the apparent diffusion coefficient were calculated. The oxidation peak current was linearly related to the concentration of DHBA in the range 0.8–1.5 mM, and the detection limit was 0.62 µM (at 3σ). The effect of potential interferents was investigated, and the method was successfully applied to the determination of DHBA in different samples. [ABSTRACT FROM AUTHOR]