In this paper the Bi (Ⅲ) -ligand(pyridine-2-carboxylic acid) system was studied by direct current sampledpolarography (DC_TAST) at a fixed ratio of total-ligand to total-metal concentration and changing pH. The po-larographic experimental complex formation curve (ECFC) and the theoretical complex formation curve (TCFC)were used for modelling the metal-ligand system and optimizing stability constants. The ECFC, in which experi-mental parameters of polarography are included (a shift in a half-wave potential and a variation in a diffusioncontrolled limiting current), appears to be a characteristic function for a particular metal-ligand system. The TCFCis a theoretical curve calculated for the designed metal-ligand model from mass-balance equation. Five bismuthcomplexes MHL, ML, ML2, ML3 and ML3(OH) with their stability constants as logβ 7.54 ±0. 10, 7.50 ±0.02,13.91 +0. 04, 18.15 ±0. 03 and 26.75 ±0. 02, respectively, are reported.
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