Highly-Sensitive Simultaneous Determination of p-Phenylenediamine and Hydroquinone by Recognizing Electrochemical Reduction Responses on Bare GCE

p-Phenylenediamine (PPD) and hydroquinone (HQ) are hair dye precursors for permanent dyeing and are used globally. We report a novel and economic approach for the selective and simultaneous detection of the cathodic peaks of PPD and HQ by using a bare glassy carbon electrode, compared with modified electrodes that are obtained by tedious or expensive functionalized and that failed to achieve a peak-to-peak separation of PPD and HQ. Linear relationships between the simultaneous cathodic peak current of PPD and HQ concentrations were obtained for 0.5–400 μM and 5–4,000 μM with detection limits (S/N = 3) of 0.163 and 0.353 μM, respectively. The glassy carbon electrode sensor was applied to determine PPD and HQ in Nanjing river water with a recovery for these two analogues of 98.7–103.9% and 98.0–102.4%, respectively.