Highly-Sensitive Simultaneous Determination of p -Phenylenediamine and Hydroquinone by Recognizing E lectrochemical Reduction Responses on Bare GCE Juanjuan Gao a,1 , Weiqing Zhu a,1 , Haiou Song b, c, * ,z , and Shupeng Zhang a,c * ,z 1 J.J. Gao a ...