4TH-DERIVATIVE SPECTROPHOTOMETRIC DETERMINATION OF NEODYMIUM IN MIXEDRARE-EARTHS WITH METHYL THYMOL BLUE AND CETYLPYRIDINIUM CHLORIDE

A sensitive and selective method is described for the determination of neodymium in mixed rare earths using fourth-derivative spectrophotome try. The method is based on the absorption spectra of 4f electron tran sitions of the complex of neodymium with methyl thymol blue and cetylp yridinium chloride. The influence of various instrumental parameters a nd reaction conditions for maximum colour development are investigated . The calibration curve is linear over the range 0-3.5 mug ml-1 neodym ium. The relative standard deviation for determination of 1.4 mug ml-1 neodymium (n = 7) is 1.6%. The detection limit (signal-to-noise ratio = 3) is 0.2 mug ml-1.