Isotachophoretic separation behavior of rare-earth EDTA chelates and analysis of minor rare-earth elements in an iron ore by bidirectional isotachophoresis–particle-induced X-ray emission

Mobilities of 16 anions of rare-earth–EDTA 1:1 chelate (RE–EDTAs) were isotachophoretically measured by using two leading electrolytes (pH 3.6 and 6.0) in order to assess their separation behavior. The leading electrolyte was 20 m M hydrochloric acid. The pH of the solution was adjusted to 3.6 by adding β-alanine and to 6.0 by adding histidine. The obtained mobilities were very close to each other in the range 20.1·10 −5–21.9·10 −5 cm 2 V −1 s −1 with the minimum mobilities for Pr–EDTA and Nd–EDTA for pH 3.6 and 6.0, respectively, and pH dependence was hardly observed. On the basis of the above knowledge, minor rare-earth elements in a standard iron ore sample were determined as RE–EDTAs by bidirectional isotachophoresis–particle-induced X-ray emission (PIXE), where the Fe(II) matrix digested by alkali fusion was separated as Fe(II)Phen 3 2+ (phen=1,10-phenanthroline). Since 5% of the total iron was still detected as Fe(III)EDTA − and might disturb PIXE analysis of RE–EDTA −, itaconic acid was used as the spacer for Fe(III)EDTA − and RE–EDTA −. The fractions of RE–EDTA − were successfully analyzed off-line by a multielemental analytical method, PIXE [analytical result (3.62% (w/w) as RE 2O 3]; the nominal value was 3.37% (w/w) as RE x O y .