Journal of Chromatography A, 802 (1998) 203–210 Separation of rare-earth ions by isotachophoresis and capillary zone electrophoresis Qinglu Mao, Yoshio Hashimoto, Yuuki Manabe, Natsuki Ikuta, Fumitaka Nishiyama, * Takeshi Hirokawa Applied Physics and Chemistry, Faculty of Engineering, Hiroshima University, Kagamiyama 1, Higashi-hiroshima 739, Japan Abstract The simultaneous separations of 15 rare-earth (RE) ions including yttrium and lanthanide both by isotachophoresis (ITP) and by capillary zone electrophoresis (CZE) were achieved by using the developed electrolyte systems containing a-hydroxyisobutyric acid (HIBA) as main complexing agent and malonic acid as the assistant one. The successful separation 31 31 31 31 of Y from Dy without loss of the separation of Eu and Gd was briefly summarized. Based on the assumed equilibria existed in steady state zone while using such an electrolyte system with binary complexing agents, the effective mobilities of the RE complex ions and the qualitative indicies (R , the ratio of the specific conductivity of the sample zone to E that of the leading zone) for the RE complex zone were theoretically simulated. The reason for the successful separation was clarified from the view of complex formation, and the simulated isotachopherogram for an optimum electrolyte system was then obtained. The validity of the simulation was checked by comparison of the simulated R with the observed ones. E Furthermore, the historic sample didym prepared from a RE ore by Brauner was analyzed by ITP–particle-induced X-ray emission as well as by CZE, where the supporting electrolyte for CZE analysis is 30 mM creatinine containing 4 mM HIBA and 0.4 mM malonic acid buffered by 2-ethylbutryric acid to pH 4.8.  1998 Elsevier Science B.V. Keywords: Isotachophoresis; Buffer composition; Complexation; Rare-earth ions; Inorganic cations; Hydroxyisobutyric acid; Malonic acid 1. Introduction importance of separation of yttrium from lanthanide ions, binary complexing agents containing HIBA as The separation of rare-earth ions plays an im- the main complexing agent and tartaric acid as the portant role in the analytical determination of the assistant one was used for the analysis of several RE rare-earth samples, especially of the ores. However, ores [4,5]. The weak point of this electrolyte system this separation is very difficult due to the highly is that the simultaneous separation of yttrium to- similar properties of RE ions. In such cases, electro- gether with lanthanide ions was not achieved. For phoresis including isotachophoresis (ITP) and capil- this reason, recently, an electrolyte system containing lary zone electrophoresis (CZE) has proved to be HIBA as the main complexing agent and malonic very powerful for the separation of lanthanide ions acid as an assistant one was successfully developed by employing a-hydroxyisobutyric acid (HIBA) as a for the simultaneous separation of yttrium and complex-forming agent [1–3]. While recognizing the lanthanide ions by ITP [6]. On the other hand, theoretical simulation has been * Corresponding author. widely accepted as a powerful method for optimizing 0021-9673 / 98 / $19.00  1998 Elsevier Science B.V. All rights reserved. PII S0021-9673(97)01093-5