Determination of rare earth elements by ion pair HPLC with post-column derivatization using Arsenazo III

Abstract

Rare earth elements can be determined on a CGC column 3 x 150 mm packed with Separon SGX C 18 modified with sorbed ammonium dodecyl sulfate (from solutions with c = 5 mmol l-1) by isocratic or stepwise gradient elution with ammonium DL-α-hydroxyisobutyrate solution (20-160 mmol l-1) at pH 4·5. The method of post-column derivatization with a solution of Arsenazo III (5 μmol l-1) in 0·1M formate buffer at pH 2·9-3·0 for photometric detection enables 10-150 or 6-155 ng of rare earth ions in sample (n = 5-7). By preconcentration on the analytical column from 0·1-2·5 ml sample volumes followed by stepwise gradient elution, 30-80 μg of rare earth ions in 1 ml sample can be determined with a reproducibility of 4% or better, the recovery being 90-106%. The procedures were applied to the determination of rare earth elements in samples of apatite, oxide concentrates and a luminophor, and a very good agreement with the results obtained by optical methods was achieved.