Determination of trace amounts of thorium and lanthanides by successive titrations using Semi-xylenol Orange with spectrophotometric end-point indication

Abstract

The precision and accuracy attainable in successive titrations of Th⁴⁺ and either La³⁺, Nd³⁺ or Gd³⁺ with a 0.001 M solution of disodium ethylenediaminetetraacetate using Semi-xylenol Orange (SXO) as a metallochromic indicator were studied. Thorium(IV) was titrated at pH 2, the pH was adjusted to 5.5–5.9 by adding hexamethylenetetramine buffer and La³⁺(or Nd³⁺ or Gd³⁺) was then titrated. A comparison of the indicators SXO and Xylenol Orange for successive titrations of Th⁴⁺ and either La³⁺, Nd³⁺ or Gd³⁺ was carried out.