Simultaneous determination of dihydroxybenzene isomers in cosmetics by synthesis of nitrogen-doped nickel carbide spheres and construction of ultrasensitive electrochemical sensor

N-doped nickel carbide spheres (N-NiCSs) were synthesised for the first time by controlling the type of surfactant, surfactant-to-Ni molar ratio, reaction temperature, and reaction time. The morphology, composition, and electrochemical behaviour of the synthesised spheres revealed that the spheres presented a large specific surface area, abundant pores, and good conductivity, with excellent electrocatalytic performance. A glassy carbon electrode-modified with N-NiCSs was used for the simultaneous identification of hydroquinone (HQ), catechol (CC), and resorcinol (RS) utilising differential pulse voltammetry. The oxidation peaks of HQ, CC, and RS were observed at 9.8, 119, and 470 mV, respectively (vs. SCE). Under optimal conditions, the oxidation peak currents of HQ, CC, and RS were linear in the concentration ranges of 0.005–100 μM, 0.05–200 μM, and 5–500 μM, respectively. The detection limits of HQ, CC, and RS were 0.00152 μM, 0.015 μM, and 0.24 μM (S/N = 3), respectively. The sensitivities of HQ, CC, and RS were 4.635, 2.069, and 0.985 μA μM−1 cm−2 (S/N = 3), respectively. The fabricated sensor was successfully used to detect HQ, CC, and RS in hair dye, whitening cream, and local tap water samples. Moreover, the sensor presented a good repeatability, reproducibility, and stability during cosmetic testing and a relatively wide linear range, an ultralow detection limit, and an ultrahigh sensitivity.