AOAC Official Method 937.05 Lactic Acid in Milk and Milk Products
Spectrophotometric Method
First Action 1937
Final Action
A. Reagents
(a) Barium lactate standard solution.—Dissolve in ca 10 mL H2O amount of a pure lactate, such as lithium, zinc, or calcium lactate, containing
equivalent of ca 300mgfree lactic acid. Transfer material to extractor, Figure 937.05, add 0.5 mL H2SO4 (1 + 1, v/v), and adjust volume to 50 mL. Extract with ether 3 h. Add ca 20 mL H2O to extraction flask, evaporate ether on steam bath, and carefully titrate with 0.05M Ba(OH)2, using phenolphthalein. Transfer neutralized material to 200 mL volumetric flask, dilute to volume, and mix. Pipet into 500 mL volumetric flask amount of this barium lactate solution containing equivalent of exactly 250 mg free lactic acid, dilute to volume,mix, and designate as lactate standard solution. (2 mL equivalent to 1 mg lactic acid. To plot standard curve, use freshly prepared solution.) Transfer 20 mL lactate standard solution to 100 mL volumetric flask, dilute to volume, and designate as dilute lactate standard solution (10 mL equivalent to 1 mg lactic acid).
