Analytical Sciences

Applicability of Capillary Electrophoresis to the Analysis of Trace Rare Earth Elements in Geological Samples

Yali SUN,* Min SUN,** and Guochun ZHAO**

*Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, China
**Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China

This study developed a methodology to analyze trace rare earth elements (REEs) in geological materials by capillary electrophoresis (CE). Changed from dilute HNO₃ into a water medium by heating, REE ions are detectable at ∼2 ng mL^-1. In the presence of coexisting elements from geological samples, REE separations were carried out. After sample fusion with Na₂O₂ and interference separation with ammonium pyrrolidinedithiocarbamate chelate, REE analytes were coprecipitated with Mg(OH)₂ at pH 8.5, and then prepared into a water medium for CE determination. Using the standard addition method, this protocol was validated by analyses with better than 5% precision. This method was applied to geological materials; the REE results are in consistence with their certified values. With electrokinetic injection, internal standard (IS) selected among lanthanides is a prerequisite of high-quality REE data. An approach was proposed to derive the IS content for further correcting its contribution from unknown samples.

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