Evaluation of a Peak Potential of an Uncomplexed Metal Ion in Speciation Study of Labile Metal–Ligand Systems by Polarography. Stability Constant Determination of CdII and PbII with Picolinic Acid at a Fixed LT:MT Ratio and Varied pH
✍ Scribed by Ignacy Cukrowski; Sharon A. Loader
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 195 KB
- Volume
- 10
- Category
- Article
- ISSN
- 1040-0397
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✦ Synopsis
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 ЊC and an ionic strength of m ¼ 0.1 and 0.5 mol dm ¹3 . 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 b found from DPP at m ¼ 0.1 mol dm ¹3 4.34 Ϯ 0.04, 8.01 Ϯ 0.04, 10.79 Ϯ 0.03, and at m ¼ 0.5 mol dm ¹3 4.29 Ϯ 0.03, 7.89 Ϯ 0.03, 10.49 Ϯ 0.02, respectively, are reported. Four lead complexes PbL, PbL 2 , PbL 3 and PbL 2 (OH) and their stability constants as log b found from DPP at m ¼ 0.5 mol dm ¹3 4.49 Ϯ 0.02, 7.58 Ϯ 0.03, 9.59 Ϯ 0.02 and 11.46 Ϯ 0.03, respectively, are reported. All stability constants at m ¼ 0.5 mol dm ¹3 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.