In the present study, an alternative platform for trace copper ions (Cu(II)) determination using a diamond electrode in combination with a disposable paper‐based analytical device (d‐PAD) has been proposed. First, the complexation between Cu(II) and 1,10‐phenanthroline ligand was adsorptively accumulated onto a paper that is directly in contact with the diamond electrode and measured via square wave anodic stripping voltammetry. Under the optimal experimental conditions, the peak current was proportional to the concentration of Cu(II) in the range of 0.4–70 ng mL−1, and the detection limit was found to be 0.1 ng mL−1. Most importantly, this platform can be successfully applied to detect trace Cu(II) in different water samples (drinking water, tap water, groundwater and river water) with satisfactory results. Thus, the proposed d‐PAD could be a highly efficient platform for trace Cu(II) determination in environmental samples.

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In this work, a novel electrochemical sensor was proposed for the simultaneous determination of fat-soluble vitamins (A, D, E, K) using a screen-printed graphene/Nafion electrode (SPGNE). The scanning electron microscopy was used for morphological characterization of the electrode surface. The electrochemical behaviors of fat-soluble vitamins have been studied in a mixture of ethanol and sodium perchlorate monohydrate using square-wave voltammetry (SWV). The results obtained indicated that the oxidation peak of each fat-soluble vitamin appeared at different potentials leading to the possibility for the simultaneous detection. The influences of experimental parameters such as the effects of proportions of ethanol, potential increment, amplitude, frequency and quiet time were examined. Under the optimized conditions, the linearity between oxidative currents and concentrations of fat-soluble vitamins ranged from 0.1 μg mL-1 to 5 μg mL-1 for vitamin A, 0.08 μg mL-1 to 5 μg mL-1 for vitamin D and E, and 0.2 μg mL-1 to 1.6 μg mL-1 for total vitamin K, with the limits of detection of 0.018, 0.013, 0.012 and 0.004 μg mL-1, respectively. These developed sensors provide high sensitivity in detection and offer high potential to apply them for the simultaneous determination of fat-soluble vitamins in dietary supplements.

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