Premium
Evaluation of a Peak Potential of an Uncomplexed Metal Ion in Speciation Study of Labile Metal–Ligand Systems by Polarography. Stability Constant Determination of Cd II and Pb II with Picolinic Acid at a Fixed L T :M T Ratio and Varied pH
Author(s) -
Cukrowski Ignacy,
Loader Sharon A.
Publication year - 1998
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/(sici)1521-4109(199810)10:13<877::aid-elan877>3.0.co;2-1
Subject(s) - polarography , chemistry , stability constants of complexes , picolinic acid , ligand (biochemistry) , metal , ionic strength , metal ions in aqueous solution , ionic bonding , analytical chemistry (journal) , cadmium , inorganic chemistry , ion , chromatography , aqueous solution , organic chemistry , biochemistry , receptor
Abstract The ligand picolinic acid was studied with Cd II and Pb II by differential pulse polarography (DPP) at fixed total ligand (L T ) to total metal (M T ) concentration ratios, varied pH at 25 °C and an ionic strength of μ = 0.1 and 0.5 mol dm −3 . The corrected peak potential of an uncomplexed metal ion E p (M Free ) is defined for the first time and used, instead of experimentally available value, to evaluate the shift in the peak potential. The polarographic experimental and calculated complex formation curves (ECFC and CCFC) were used for modeling of the metal–ligand systems and the refinement of stability constants. It has been shown that with the use of the corrected value of E p (M Free ) together with the ECFC and CCFC it is possible to reproduce values of stability constants obtained by glass electrode potentiometry. Three cadmium complexes CdL, CdL 2 and CdL 3 and their stability constants as log β′ found from DPP at μ = 0.1 mol dm −3 4.34 ± 0.04, 8.01 ± 0.04, 10.79 ± 0.03, and at μ = 0.5 mol dm −3 4.29 ± 0.03, 7.89 ± 0.03, 10.49 ± 0.02, respectively, are reported. Four lead complexes PbL, PbL 2 , PbL 3 and PbL 2 (OH) and their stability constants as log β′ found from DPP at μ = 0.5 mol dm −3 4.49 ± 0.02, 7.58 ± 0.03, 9.59 ± 0.02 and 11.46 ± 0.03, respectively, are reported. All stability constants at μ = 0.5 mol dm −3 and two lead complexes PbL 3 and PbL 2 (OH) are reported for the first time, whereas the formation of the complex CdL 3 has been confirmed by DPP. Results obtained in this work are compared with the literature data.