CENTRIFUGAL PARTITION CHROMATOGRAPHIC-SEPARATION OF TERVALENT LANTHANIDES USING ACYLPYRAZOLONE EXTRACTANTS

The separation of tervalent lanthanides (M3+) by centrifugal partition chromatography (CPC) with the extractants 1-phenyl-3-methyl-4-benzoyl -5-pyrazolone (HPMBP, HL) and 1-phenyl-3-methyl-4-capryloyl-5-pyrazolo ne (HPMCP, HL) in the toluene-water phase pair and the factors influen cing the separation efficiencies have been investigated. The CPC effic iencies are mainly limited by the slow dissociation of the M3+-acylpyr azolone complexes (ML3) occurring exclusively at the toluene-water int erface, as indicated by a direct linear correlation between the reduce d plate heights (CETPck) and the half-lives (t(1/2)) of the dissociati on of the ML3 complexes determined by independent kinetic studies, The lanthanide-acylpyrazolone system represents the first example of a se paration by multistage countercurrent distribution wherein the efficie ncies are mainly limited by interfacial processes analogous to convent ional liquid chromatographic systems, Dramatic improvements in the eff iciencies of these separations could be obtained by the addition of th e neutral surfactant Triton X-100 to the toluene phase and the metallo chromic indicator Arsenazo III (AZ) to the aqueous phase. The improvem ent in the efficiencies with Triton X-100 was due to the increased int erfacial areas resulting from the adsorption of the surfactant, and th at in the case of AZ was due to the increased interfacial area and int erfacial catalysis of the formation and dissociation of the ML3 comple xes. As a result, the addition of AZ provided much higher efficiencies than did the addition of Triton X-100. Further, the addition Triton X -100 did not significantly alter the selectivities of the ligands for M3+, but the addition of AZ resulted in much poorer selectivities, Sig nificant differences were observed in the efficiencies of separations with HPMBP and HPMCP under various experimental conditions, which stem from differences in the interfacial dissociation rate constants of ML 3 complexes and the interfacial areas generated, indicating that CPC s eparation of tervalent lanthanides with acylpyrazolones in the toluene -water phase pair is driven mainly by interfacial processes.