1 SCOPE AND FIELD OF APPLICATION This International Standard specifies a titrimetric method for the determination of the carbonates content of sodium hydroxide for industrial use. The method is applicable to products having carbonates contents, expressed as CO*, greater than 0,Ol % (mlm) : Three cases, selected by a preliminary test, are envisaged : 1.1 Sodium hydroxide containing neither sulphides nor chlorates. 1.2 Sodium hydroxide containing sulphides. 1.3 Sodium hydroxide containing chlorates.