The study is focused on the electrochemical behavior of the toxic metals Cu(II), Pb(II), and Cd(II) ions in the presence of the thiosemicarbazides derivatives. Important effects of adsorption of the organic reagents and their metal complexes on the mercury dropping electrode are shown. An original method for evaluation of the stability constant of the adsorpted species has been proposed. It was demonstrated that the monosubstituted potassium phthalate (KHPh) in the system Сd(П) - 4-phenylthiosemicarbazde (4-FTSC) plays an important role not only for stabilization of pH, but it is also favorable for the formation and stabilization of the electroactive species. Introduction of the phenyl radical in the thiosemicarbazide molecule increases the sensitivity of the analytical signal and makes possible the determination of the cadmium content up to the nanomolar concentration.Substitution of the sulfur atom by oxygen in the molecule of 8-quinolinaldehyde thiosemicarbazone changes the selectivity of the organic reagent. In the presence of 8-quinolinaldehyde semicarbazone, it is possible the selective determination of the lead, reducing 2-3 times the mass of the samples. Using the adsorptive accumulation on the electrode, a number of original methods for determination of the heavy metal in different systems have been developed. The 4-phenylthiosemicarbazide (4-FTSC) has been proposed for determination of the cadmium in river waters (fig.1), the thiosemicarbaziddiacetic acid (TSCDAA) and 8-quinolinaldehyde thiosemicarbazide – for copper determination in the river waters (fig.2), apple and tomato juices, 8-quinolinaldehyde semicarbazone - for determination of the lead in wheat flour and petrol. The metrological parameters of the proposed methods have been evaluated using standard additions, AAS spectrometry, and reference materials.