STUDY OF ISOTACHOPHORETIC SEPARATION BEHAVIOR OF METAL-CATIONS BY MEANS OF PARTICLE-INDUCED X-RAY-EMISSION .2. SEPARATION EFFICIENCY OF LANTHANOID MODEL MIXTURE

The isotachophoretic (ITP) separation behaviour of fourteen lanthanoid cations coexisting with alpha-hydroxyisobutyric acid was studied in relation to the separation efficiency. It was confirmed that the stimulated separation efficiencies using approximate equations agreed well with the observed values, except for Eu-Gd. It was found that the separation efficiency of equimolar amounts of neighbouring lanthanoids varied discontinuously but periodically, forming four different groups ("tetrad effect"). The effect of the component ratio on the separation efficiency of minor lanthanoids from major components was studied by means of ITP fractionation and subsequent off-line analysis by particle-induced X-ray emission. It was confirmed that the separation efficiency of multi-component mixtures decreased with decrease in the abundance of the sample. For binary mixtures of neighbouring lanthanoids, however, the separability was almost independent of the abundance, as for strong electrolytes.