Application of chitosan and its N-heterocyclic derivatives for preconcentration of noble metal ions and their determination using atomic absorption spectrometry.

Chitosan and its N-heterocyclic derivatives N-2-(2-pyridyl)ethylchitosan (2-PEC), N-2-(4-pyridyl) ethylchitosan (4-PEC), and N-(5-methyl-4-imidazolyl) methylchitosan (IMC) have been applied in group preconcentration of gold, platinum, and palladium for subsequent determination by atomic absorption spectroscopy (AAS) in solutions with high background concentrations of iron and sodium ions. It has been shown that the sorption mechanism, which was elucidated by XPS, significantly influences the sorption capacity of materials, the efficiency of metal ions elution after preconcentration, and, as a result, the accuracy of metal determination by AAS. We have shown that native chitosan was not suitable for preconcentration of Au(III), if the elution step was used as a part of the analysis scheme. The group preconcentration of Au(III), Pd(II), and Pt(IV) with subsequent quantitative elution using 0.1M HCl/1M thiourea solution was possible only on IMC and 4-PEC. Application of IMC for analysis of the national standard quartz ore sample proved that gold could be accurately determined after preconcentration/elution with the recovery above 80%.

Synthesis and properties of isomeric pyridyl-containing chitosan derivatives.

Here we report on the method of synthesis in gel of a new heterocyclic aminopolymer-N-2-(4-pyridyl)ethylchitosan (4-PEC) via direct addition of 4-vinylpyridine to chitosan that yields a derivative with the substitution degree (DS) up to 0.8. The comparison of reactivity, thermal, spectroscopic, and sorption properties of a new derivative and its isomer N-2-(2-pyridyl)ethylchitosan (2-PEC) is presented. 2-PEC has higher sorption capacity and forms more stable chelates with [PdCl4](2-) and [PtCl6](2-) ions than 4-PEC, but the latter shows higher selectivity to noble metals ions in the presence of Cl(-) ions. A gradual increase of the sorption capacities and the affinity coefficient for Cu(2+) and Ni(2+) in the row chitosan<4-PEC<2-PEC was related to the increase of electron donor nitrogen atoms content and chelating properties of 2-PEC. A nearly negligible increase of the 4-PEC sorption capacity for Ag(+), as compared to plain chitosan, was suggested to be dependent on the difference in complexation models for 2-PEC and 4-PEC derivatives. The density functional theory (DFT) calculations have shown that the "pendant" model of the complex with Ag(I) is energetically favorable only for 2-PEC derivative, while in cases of chitosan and 4-PEC only "bridge" complexes can be formed that results in lower sorption capacity.

N-(2-(2-pyridyl)ethyl)chitosan: Synthesis, characterization and sorption properties.

The method of producing N-2-(2-pyridyl)ethylchitosan (PE-chitosan) with substitution degrees (DS) up to 1.2 has been developed using the "synthesis in gel" approach for direct addition reaction between 2-vynilpyridine and chitosan. Investigation of sorption properties has revealed significantly higher affinity of pyridylethyl fragments to Pt(IV)) and Pd(II) ions compared to the unsubstituted amino groups of chitosan. The maximum sorption capacities of PE-chitosan in 0.1M HCl solution were estimated as 5.56mmol/g for Au(III), 3.67mmol/g for Pd(II), and 2.75mmol/g for Pt(IV). Sorption capacities of PE-chitosan for transition metal ions at pH 4-8 were 1.5-2.6 higher than those of chitosan with the highest values attained for Cu(II) and Ag(I) ions - 1.50mmol/g and 1.53mmol/g, respectively. The PE-chitosan application for preconcentration of Au(III) with subsequent elution with HCl/thiourea mixtures was proved to be efficient for atomic absorption spectroscopy analysis of multi-component solutions with low gold content.