Journal
ELECTROPHORESIS
Volume 29, Issue 10, Pages 2041-2050Publisher
WILEY
DOI: 10.1002/elps.200700764
Keywords
capillary electrophoresis; carbonate; complex; inductively coupled plasmamass spectrometry; lanthanides
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The electrophoretic mobilities (mu(ep,Ln)) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L-1 Alk(2)CO(3) aqueous solutions for Alk(+) = Li+, Na+, K+ and Cs+. In 0.5 mol L-1 solutions, two different mu(ep,Ln) values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO3)(3)(3-) and Ln(CO3)(4)(5-) stoichiometries for the heavy (small) mu(Alk2CO3)(ep,Ln) and the light (big) lanthanides, respectively. The Alk(+) counterions influence the mu(ep,Ln) (Alk2CO3) values, but not the overall shape of the pep,Ln plots as a function of the lanthanide atomic numbers: the counterions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk(+) counterions decreases in the Li+ > Na+ >> K+ > Cs+ series. The K-3,K-Ln stepwise formation constants of the Ln(CO3)(3)(3-) complexes slightly increase with the atomic numbers of the lanthanides while K-4,K-Ln, the stepwise formation constants of Ln(CO3)(4)(5-) complexes, slightly decrease from La to Th, and is no longer measurable for heavier lanthanides.
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