After that the ash was dissolved with 10 ml of concentrated HCl and diluted to 50 ml with distilled water and 1 mol l−1 NaOH so that the final pH was ca 1. For the analysis, 0.5 ml of the obtained solution was transferred into a 25-ml calibrated flask
and 0.02 g aluminum metal was added in order to reduce Sn(IV) to Sn(II).