ISO 3697:1976

Sodium hydroxide for industrial use — Determination of calcium and magnesium contents — Flame atomic absorption method

Applicable to products having contents of more than 2.5 mg Ca/kg and 0.5 mg Mg/kg if an acetylene-air flame is used or 0.6 mg Ca/kg and 1.0 mg Mg/kg if an acetylen-dinitrogen monoxide flame is used. The principle consists in the acidification of a test portion with hydrochloric acid, aspiration of the solution into an acetylene-dinitrogen monoxide flame or acetylene-air flame. In the latter case, addition of lanthanum ions in order to suppress certain interferences. Measurement of the absorption of the 422.7-nm and 285.2-nm lines emitted by calcium and magnesium hollow-cathode lamps.