Stoyanov A. Determination of the multivalent forms of cerium and europium in poorly soluble functional inorganic materials

The dissertation is devoted to the development of spectrometric procedures for the determination of Ce(III, IV) and Eu(II, III) in poorly soluble functional inorganic materials.It was shown that diffuse reflectance spectroscopy can be used for quick detection of multivalent forms of cerium in the materials based on its fluorides without samples destruction. It was found that phosphoric acid is a suitable solvent for compounds of cerium and europium because it does not change the degree of oxidation and the resulting complex stabilizes europium (II, III) and cerium (III, IV) ions.For the detection and determination of the Ce(IV) in the fluoride samples, the difference in the absorption spectra of phosphate complexes of Ce(III) and Ce(IV) was used. In the range of the 320-400 nm Ce(III) phosphate complex, contrary to Ce(IV) complex, have no absorption at all. Thus spectrophotometrical determination of the Ce(IV) in the presence of the Ce(III) is possible in a wide concentration range. For detection of the Ce(III) in the presence of the Ce(IV), the method of a first derivative of the absorption spectra was used. In the presence of up to 8-fold excess of the Ce(IV), more than 2 mkg/ml of the Ce(III) can be determined. To determine the amount of Ce(III) in samples containing mainly Ce(IV), a method based on Ce (III) oxidation to Ce (IV) by the solution of potassium permanganate was proposed. The content of Ce (III) was determined by spectrophotometrical measuring of the reduction of optical absorbance of the KMnO4. To determine the amount of Ce(IV) in the presence of an excess of Ce(III), we developed a method based on spectrophotometrical measuring of the reduction of optical absorbance of the organic dyes because of oxidation by cerium (IV). To determine Eu(II) in poorly soluble inorganic materials a combination of the dissolution procedure with analytical oxidation of europium (II) by V(V) was used. Determination of low contents of the europium (II) was carried out by an equivalent content of the vanadium (IV) that had been formed. The procedure is based on the oxidation of vanadium (IV) by the solution of potassium permanganate followed by measuring the optical absorbance of excess MnO4[-]-ions. By proposed procedures, the samples with different ratios of europium and cerium valence forms have been analyzed.