Determination of rare earths by high-performance liquid chromatography with post-column derivatization

Post-column derivatization of the lanthanides has been developed for HPLC. Following ion exchange separation the column effluent and reagent are mixed in a mixing unit (mixing tees and reaction coil). The reagent solution which consists of arsenazo III (0.06%) in chloroacetic acid buffer (0.15 M, pH 2.5) is pumped at a rate of 0.35 ml/min. The effluent and reagent then enter an UV-vis spectrophotometric detector for measurement of the absorption at 665 nm. The effects of the background absorbance of the reagent, the fluctuations in flow, the concentration of α-hydroxyisobutyric acid, the types of various gradient elution as well as wavelength of metal complex on the separations have also been discussed. The limit of detection of 20 ng at a signal to noise ratio of 2.5:1 was given. This technique has been used for the determination of rare earth impurities in high purity neodymium oxide