AOAC Official Method 932.05 Citric Acid in Milk
Gravimetric Method
First Action 1932
Final Action
A. Preparation of Test Portion
To 50 g milk in 150 mL beaker, add ca 100 mg tartaric acid and 6 mL 0.5M H2SO4, and heat on steam bath 15 min. Immediately add 3mL20% phosphotungstic acid solution (w/v), mix well, and return to steam bath for 5 min. Transfer to 250mLvolumetric flask with alcohol, cool, dilute to volume with alcohol, mix, and filter through folded paper. Pipet 200 mL clear filtrate into centrifuge bottle.
B. Reagents
(a) Potassium permanganate solution.—Dissolve 5 g KMnO4 in H2O and dilute to 100 mL.
(b) Ferrous sulfate solution.—Dissolve 200 g FeSO4×7H2O in H2O, dilute to 500 mL with H2O, and add 5 mL H2SO4.
(c) Lead acetate solution.—Dissolve 75 g Pb(CH3COO)2×3H2O in H2O, add 1 mL CH3COOH, and dilute to 250 mL.
