AOAC Official Method 939.11 Fluoride in Water Colorimetric Method
First Action 1939
Final Action
A. Reagents
(a) Fluoride standard solution.—0.01 mg F/mL. Dissolve 2.21 g NaF (minimum purity 98%) in 1 L H2O. Dilute 10 mL of this solution to 1 L.
( b ) Thorium n i t r a t e s o l u t i o n.—Dissolve 0.25 g
Th(NO3)4×12H2O or 0.2 g Th(NO3)4×4H2O in 1 L H2O.
(c) Alizarin red indicator.—0.01% aqueous solution sodium alizarin sulfonate (alizarin red S).
(d) Hydrochloric acid.—Exactly 0.05M.
(e) Sodium hydroxide solution.—Exactly 0.05M.
(f) Hydroxylamine hydrochloride solution.—1.0 g/100 mL.
