CHEMOMETRIC ALTERNATIVES FOR RESOLUTION OF CLASSICAL ANALYTICAL PROBLEMS - SPECTROPHOTOMETRIC DETERMINATION OF LANTHANIDE MIXTURES

The simultaneous determination of lanthanide family elements is one of the greatest problems in analytical chemistry, due to the close simil arity of their chemical properties. Spectrophotometric methods are gen erally of limited use, due to the Various mutual spectral interference s involved. By using multivariate calibration methods (partial least-s quares regression, PLSR), it was possible to obtain a model that adjus ts itself perfectly to the values of the mixture concentrations used i n the calibration. The model used absorption spectra in the 290-800 nm range for a set of 20 different mixtures of Ce, Pr, Nd and Sm, and ma de possible the determination of Ce, Pr and Nd concentrations of a com mercial rare-earth product, with significantly greater precision than the conventional univariate calibration method. Determination of the S m concentrations was not possible, since its concentration was below t he concentrations used in the model definition. (C) 1997 Elsevier Scie nce B.V.