SELECTIVE DETERMINATION OF HOLMIUM IN RARE-EARTH MIXTURES BY 2ND-DERIVATIVE SPECTROPHOTOMETRY WITH BENZOYLINDAN-1,3-DIONE AND CETYLPYRIDINIUM CHLORIDE

The absorption spectra of 4f electron transitions of the holmium compl ex with benzoylindan-1,3-dione and cetylpyridinium chloride were studi ed by conventional and derivative spectrophotometry, The molar absorpt ivity of the complex at the maximum absorption band was about 22 times greater (at 450 nm) than that in the absence of the complexing agent, The use of second-derivative spectra both eliminates the interference from other rare earths and improves the sensitivity for holmium, The calibration graph showed that the complex obeys Beer's law up to 25 mu g cm(-3) of holmium, The corresponding value of Sandell's sensitivity is 0.36 mu g cm(-2). The RSD evaluated from 11 independent determinat ions of 10 mu g of holmium is 0.96%, The detection limit, obtained fro m the sensitivity of the calibration graph and for 3s(b) (s(b) = stand ard deviation of a blank without holmium, n = 11), was found to be 0.4 3 mg dm(-3) of holmium. The quantification limit, obtained for 10s(b), was 1.43 mu g cm(-3) of holmium, A method for the direct determinatio n of holmium in rare earth mixtures with good selectivity and accuracy is described.