Acide phosphorique et phosphates de sodium à usage industriel (y compris les industries alimentaires) — Dosage du fluor — Méthode photométrique au complexone d'alizarine et nitrate de lanthane

Applicable to products the F content of which is equal to or more than 0.5 mg/kg. Specifies the separation of the element from a test portion by steam distillation in a phosphoric acid medium. Formation of a blue-coloured complex with a combined reagent alizarin complexone/lanthanum nitrate in a buffered medium at the pH of 4.6. Addition of acetone to increase the stability of the complex and the sensitivity. Photometric measurement of the complex at a wavelength of about 600 nm.