Herein, a highly sensitive and selective simultaneous electrochemical method to monitor the emerging organic contaminants tartrazine (TRT), dexamethasone (DMZ) and diclofenac (DCL) in sewage treatment plants was developed. The sensing was based on electroreduction of TRT (-0.22 V), DMZ (-0.93 V) and DCL (-1.12 V) on hanging mercury drop electrode (HMDE), using citrate buffer pH 2.5 as electrolyte. The fast electrodic kinetics of these chemicals provided improvements on selectivity at high scan rates. The unique electrochemical properties of HMDE were associated to analytical performance of the square-wave voltammetry to quantify trace concentrations of TRT, DMZ and DCL, with detection limits ranging from 2.78 x 10(-8) to 1.48 x 10(-7) mol L-1. After wastewater treatment by using solid-phase extraction, the proposed procedure was successfully applied for the direct quantification of the studied compounds with high precision, accuracy and stability of the measurements, even in the presence of other electroactive contaminants. (C) 2015 Elsevier B.V. All rights reserved.