Abstract
The masking properties of thiopyrine in chelatometric titrations was examined. With the use of this reagent at pH 1.5-4 or pH 5-6, it is possible to determine thorium(IV), bismuth(III), zirconium(IV), iron(III), nickel(II), zinc(II), lead(II), cobalt(II), cadmium (II), and aluminium(III) in the presence of mercury(II), thallium(III), and copper(II). Also at pH 10-12, mercury(II) can be selectively masked in the titration of nickel(II), calcium(II), and magnesium(II). Thiopyrine reacts with the EDTA complexes of mercury(II), thallium(III), and copper(II), and liberates EDTA quantitatively. This reaction was applied to the separatory titration of mercury(II), thallium(III), or copper(II) and various metal ions with a good result.
