A recently proposed electroanalytical method, using differential pulse voltammetry (DPV) on the rotating Au-disk electrode, and electrospray ionization mass-spectrometry (ESI-MS) has been applied to study the binding of the pharmaceutical chelating agents meso-2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropanesulfate (DMPS) and d-penicillamine ( d-Pen) with Hg 2+. From the use of voltammetric titrations it was possible to obtain a detailed picture of the complexation processes at concentrations much lower than in previous studies. Predominant species were Hg(Pen) 2, Hg 2(DMSA) 2 and Hg(DMPS) 2. For Pen, Hg(Pen) was also deduced from DPV data, while Hg 2(Pen) 4 from ESI-MS. For DMSA and DMPS, Hg 2L species were detected by DPV, and Hg 2L 3, Hg 3L 3 as well as Hg 2(DMPS) 2 and Hg(DMSA) 2 by ESI-MS. When possible, DPV data were analyzed by multivariate curve resolution with alternating least squares (MCR–ALS).