Detection of rare earth elements by post‐column reaction with xylenol orange and cetylpyridinium bromide

Rare earth elements have been separated by HPLC on octadecyl‐bonded silica gel, dynamically modified with ammonium dodecylsulfate, using aqueous solutions of α‐hydroxyisobutyric acid as mobile phase. The requirements and characteristics of post‐column reaction with xylenol orange and cetylpyridinium bromide were investigated and optimized, and the reaction found to be highly sensitive and sufficiently rapid. The absorbance of the complex at 598 nm was not affected by the presence of α‐hydroxyisobutyric acid at concentrations of the latter up to 150 mmol/l; at higher concentrations of the acid, the absorbance decreased slightly. For most of the rare earth elements the response was linear up to 0.2 mmol/l; the relative standard deviation of peak area was, typically, ∼1 %. The sensitivity of the method was usually better than 1 μg/ml. The results obtained from the determination of lanthanum, cerium, praseodymium, and neodymium in samples of apatite and bastnesite were in a good agreement with those obtained by ICP‐AES. Copyright © 1992 Dr. Alfred Huethig Publishers