Journal of Chromatography A, 990 (2003) 335–341 www.elsevier.com / locate / chroma Application of electrokinetic supercharging capillary zone electrophoresis to rare-earth ore samples * Hikaru Okamoto, Takeshi Hirokawa Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University,1-4-1 Kagamiyama 1, Higashi-Hiroshima 739-8527, Japan Abstract Capillary zone electrophoresis (CZE) using electrokinetic injection (EKI) with transient isotachophoresis, which was named ‘‘electrokinetic supercharging-CZE ’’ (EKS-CZE), was applied to model samples of rare-earth ores (xenotime and monazite) and a real sample of monazite ore, the abundance of the components being greatly different among samples. When simple EKI was applied, separation and detection of rare-earth ions with smaller mobilities than the major component became difficult with an increase of the content of the major component. In contrast, when EKS-CZE was applied, the minor components (Er, Tm, Yb) with contents less than 0.025% (rare-earth/total rare-earth) could be analyzed. The analytical results for minor components in monazite ore agreed with those obtained by isotachophoresis–particle-induced X-ray emission (ITP–PIXE) and inductively coupled plasma atomic emission spectrometry (ICP-AES) with errors less than 17%. The sample amount required for analysis was 9 mg which is 200-fold smaller than that used in ITP-PIXE analysis. Analytical sensitivity of EKS-CZE was comparable with that of ICP-AES.  2003 Elsevier Science B.V. All rights reserved. Keywords: Electrokinetic supercharging; Injection methods; Rare earth ions 1. Introduction powerful for capillary zone electrophoresis (CZE) analysis. The procedure of EKS-CZE is as follows: On-line preconcentration methods such as field- after filling the separation capillary with supporting enhanced sample stacking [1–3], transient isotacho- electrolyte, appropriate amount of a leading elec- phoresis (tr-ITP) [3–7], and electrokinetic injection trolyte was filled and electrokinetic injection was (EKI) [8] have been widely used to improve con- performed. After sampling, terminating electrolyte centration sensitivity of capillary electrophoresis was filled subsequently and separation voltage was (CE), which is inherently low due to geometrical applied. This procedure enabled introduction of a restriction. Recently we have proposed EKI with large amount of sample components from a dilute tr-ITP for preconcentration, and the approach was sample without deteriorating separation. Consequent- named ‘‘electrokinetic supercharging’’ (EKS) [9]. ly, we could analyze 15 rare-earth ions (0.5 mg/l for Although the method is virtually a combination of each) and the found low limit of detectable con- two already-known techniques, we found it was quite centration was 0.3 mg/l (1.2 nM for Er, S / N53) [9], which is comparable or even better than that of ion chromatography or inductively coupled plasma *Corresponding author. Tel.: 181-824-227-111; fax: 181-824- atomic emission spectrometry (ICP–AES). 227-192. E-mail address: hiro77@hiroshima-u.ac.jp (T. Hirokawa). In our previous studies [9–13], preconcentration 0021-9673 / 03 / $ – see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016 / S0021-9673(03)00054-2