title: Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: a capillary electrophoresis-mass spectrometry study.
abstract: 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) Alk2 CO3 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) and the light (big) lanthanides, respectively. The Alk+ counterions influence the mu ep,Ln Alk2 CO3 values, but not the overall shape of the mu ep,Ln Alk2 CO3 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 K3,Ln stepwise formation constants of the Ln(CO3)3(3-) complexes slightly increase with the atomic numbers of the lanthanides while K4,Ln, the stepwise formation constants of Ln(CO3)4(5-) complexes, slightly decrease from La to Tb, and is no longer measurable for heavier lanthanides.
authors.affiliation: CEA Laboratoire de Spéciation des Radionucléides et des Molécules, Gif-sur-Yvette, France. violaine.philippini@cea.fr
authors.forename: Violaine
authors.initials: V
authors.lastname: Philippini
authors.forename: Thomas
authors.initials: T
authors.lastname: Vercouter
authors.forename: Jean
authors.initials: J
authors.lastname: Aupiais
authors.forename: Sylvain
authors.initials: S
authors.lastname: Topin
authors.forename: Chrystel
authors.initials: C
authors.lastname: Ambard
authors.forename: Annie
authors.initials: A
authors.lastname: Chaussé
authors.forename: Pierre
authors.initials: P
authors.lastname: Vitorge
mesh_terms: D002254:Carbonates / Q000737:chemistry / Q000302:isolation & purification; D004573:Electrolytes; D019075:Electrophoresis, Capillary / Q000379:methods*; D028581:Lanthanoid Series Elements / Q000737:chemistry / Q000302:isolation & purification*; D013058:Mass Spectrometry / Q000379:methods*; D012996:Solutions
chemical_list: D002254:Carbonates; D004573:Electrolytes; D028581:Lanthanoid Series Elements; D012996:Solutions