Electrochemical cells, polarization, overpotential, iR drop, electrochemical devices, two- and three-electrodes circuitation, reversibility in electrode processes, mass transfer to the electrode. Cronoamperometry, polarography, voltammetry, stripping methods. The mass spectrometer (MS). Ionization systems and sample introduction devices. Analyzers and their resolution. Detectors. MS/MS, GC-MS, SFC-MS and HPLC-MS couplings. The validation of an analytical method in terms of LoD, LoQ, linearity, precision and trueness.