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

Abstract

SummaryRare earth elements have been separated by HPLC on octadecyl-bonded silica gel, dynamically modified with ammonium dodecylsulfate, using aqueous solutions of a-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 a-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 pg/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. microbore cation-exchange column using an HIBA pH gradient, and monitored at 630 nm. The reaction conditions were not, however, studied and relatively high concentrations of XO (5 mmol/l) and CPB (10 mmol/l) in 20 % v/v methanol and concentrated ammonia buffer (pH 8.7) were used and values of molar absorptivities estimated from a chromatogram are rather low.Recently, a highly sensitive spectrophotometric method was proposed [8] Under optimum conditions (0.06 mmolil XO, 0 6 mmol/l CPB. and 0.01 moll1 acetate buffer, pH 4.5) the highest sensitivities were obtained at 610 nm; a t 600 nm the values of conditional molar absorptivities were between 80000 and 93000 mmol-'cm2 (detection limits 0.01-0.05 kg/ml) for all lanthanides.In this work, post-column derivatization of REE by reaction with XO and CPB has been studied and optimized. A sensitive method has been developed for the detection of REE after separation with HIBA solution on a dynamic ion exchanger.