Photometric micro-determination of scandium and lanthanides by direct and successive titration using semi-xylenol orange

Abstract

The precision and accuracy attainable in direct titrations of the Sc³⁺, La³⁺ or Er³⁺ ion with a 0.001 M solution of the disodium salt of EDTA using semi-xylenol orange (SXO) as a metallochromic indicator were studied. Accurate results can be achieved by successive titration. The Sc³⁺ ion is titrated at pH 2.4, the pH is adjusted to 5.6–5.9 by adding hexamethylenetetramine buffer solution and the La³⁺ ion (or Er³⁺ ion) is then titrated. A comparison of SXO and xylenol orange indicators for the successive titration of the Sc³⁺ ion and lanthanum or erbium was carried out.