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The simultaneous voltammetric determination of melatonin (MT) and pyridoxine (PY) has been carried out at a cathodically pretreated boron‐doped diamond electrode. By using cyclic voltammetry, a separation of the oxidation peak potentials of both compounds present in mixture was about 0.47 V in Britton‐Robinson buffer, pH 2. The results obtained by square‐wave voltammetry allowed a method to be developed for determination of MT and PY simultaneously in the ranges 1–100 μg mL−1 (4.3×10−6–4.3×10−4 mol L−1) and 10–175 μg mL−1 (4.9×10−5–8.5×10−4 mol L−1), with detection limits of 0.14 μg mL−1 (6.0×10−7 mol L−1) and 1.35 μg mL−1 (6.6×10−6 mol L−1), respectively. The proposed method was successfully to the dietary supplements samples containing these compounds for health‐caring purposes.

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An electrochemical sensor based on the electrocatalytic activity of graphene (GR) was prepared, and used for the individual, selective and simultaneous determination of 5‐O‐Caffeoylquinic acid (5‐CQA) that is major compound of chlorogenic acids in coffee, vanillin (VAN) and caffeine (CAF). The electrochemical behaviors of these compounds on GR modified glassy carbon electrode (GR/GCE) were investigated by cyclic voltammetry and square‐wave adsorptive stripping voltammetry. By using stripping conditions after 30 s accumulation under open‐circuit voltage, the electrochemical oxidation peaks appeared at +0.53, 0.83 and 1.39 V in phosphate buffer pH 2.5, and good linear current responses were obtained with detection limits of 4.4×10−9, 5.0×10−7, and 3.0×10−7 M for 5‐CQA, VAN and CAF, respectively. The potential applicability of the proposed method was illustrated in commercial food and beverage samples.