Lactic Acid

Propanoic acid, 2-hydroxy-.
Lactic acid [50-21-5].
» Lactic Acid is a mixture of lactic acid (C3H6O3) and lactic acid lactate (C6H10O5) equivalent to a total of not less than 88.0 percent and not more than 92.0 percent, by weight, of C3H6O3. It is obtained by the lactic fermentation of sugars or is prepared synthetically. Lactic Acid obtained by fermentation of sugars is levorotatory, while that prepared synthetically is racemic. [note—Lactic Acid prepared by fermentation becomes dextrorotatory on dilution, which hydrolyzes l-()-lactic acid lactate to l-(+)-lactic acid.]
Packaging and storage— Preserve in tight containers.
Labeling— Label it to indicate whether it is levorotatory or racemic.
Identification— It meets the requirements of the test for Lactate 191.
Specific rotation 781A: between 0.05 and +0.05, for racemic Lactic Acid.
Readily carbonizable substances— Rinse a test tube with sulfuric acid TS, and allow to drain for 10 minutes. Add 5 mL of sulfuric acid TS to the test tube, carefully overlay it with 5 mL of Lactic Acid, and maintain the tube at a temperature of 15: no dark color develops at the interface of the two acids within 15 minutes.
Residue on ignition 281: not more than 3 mg, from a 5-mL portion (0.05%).
Sugars— To 10 mL of hot alkaline cupric tartrate TS add 5 drops of Lactic Acid: no red precipitate is formed.
Chloride— To 10 mL of a solution (1 in 100) acidified with nitric acid add a few drops of silver nitrate TS: no opalescence is produced immediately.
Sulfate— To 10 mL of a solution (1 in 100) add 2 drops of hydrochloric acid and 1 mL of barium chloride TS: no turbidity is produced.
Limit of citric, oxalic, phosphoric, or tartaric acid— To 10 mL of a solution (1 in 10) add 40 mL of calcium hydroxide TS, and boil for 2 minutes: no turbidity is produced.
Assay— To about 2.5 mL of Lactic Acid, accurately weighed in a tared 250-mL flask, add 50.0 mL of 1 N sodium hydroxide VS, and boil the mixture for 20 minutes. Add phenolphthalein TS, and titrate the excess alkali in the hot solution with 1 N sulfuric acid VS. Perform a blank determination (see Residual Titrations under Titrimetry 541). Each mL of 1 N sodium hydroxide is equivalent to 90.08 mg of C3H6O3.
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