Determination of tin in iron and steel by chelatometric titration method

Steel sample was decomposed in nitric-perchloric acid mixure and heated to white fuming for precipitation of silicon, tungsten, etc. The precipitate was filtered off and the filtrate was treated with sufficient EDTA and beryllium sulfate solution for masking of iron and others. Ammonium hydroxide was added to pH 89, and the solution was boiled for min. for precipitation of tin and beryllium as their hydroxides and for separation from iron and others. The precipitate was filtered, washed with NH4OH (2+ 100) containing EDTA and taken up in H2SO4 (1+ 5). It was heated with KClO3 to white fuming to destroy any contaminating EDTA and excess KClO3. The residue was taken up in water. A trace of iron was reduced by an addition of ascorbic acid. A definite amount of standard EDTA solution was added in a slight excess against Sn, ammonium acetate added to pH and Sn was estimated by the back titration of EDTA with standard thorium solution using Xylenol Orange as an idicator.