Applications of sensitised reactions. Spectrophotometric determination of tin in steel with catechol violet and cetyltrimethylammonium bromide

Abstract

Modification of the visible spectrum of the catechol violet-tin(IV) complex by the addition of surfactants and basic dyes has been studied in an attempt to improve the catechol violet procedure for determining tin. On adding cetyltrimethylammonium bromide, the cetyltrimethylammonium salt of the catechol violet-tin(IV) complex anion is probably formed in colloidal solution and dispersed by the excess of the surfactant. The Brilliant green cation reacts with the complex anion in a similar manner and the salt formed can be dispersed with poly(vinyl alcohol). In the latter instance, however, the bathochromic shift in the main absorption band of the complex is not associated with increased sensitivity.

The spectrophotometric method of determining tin with catechol violet and cetyltrimethylammonium bromide has been modified and applied to the determination of tin in steel. Preliminary separation of tin is achieved by extracting tin(IV) iodide into toluene. Results obtained with a wide range of British Chemical Standard steels indicate a high precision for the recommended procedure. Lactic acid is used to mask molybdenum, chromium, vanadium, nickel and cobalt, which interfere at the levels that are commonly found in steels. The recommended procedure is not applicable to steels with copper to tin ratios greater than 20 : 1 owing to precipitation of copper(I) iodide at the extraction stage.