Ascorbic Acid
(as kore' bik as' id).
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C6H8O6 176.12
l-Ascorbic acid     [50-81-7].
DEFINITION
Ascorbic Acid contains NLT 99.0% and NMT 100.5% of C6H8O6.
IDENTIFICATION
•  B. A 20-mg/mL solution reduces alkaline cupric tartrate TS slowly at room temperature but more readily upon heating.
ASSAY
•  Procedure
Sample:  400 mg of Ascorbic Acid
Titrimetric system 
Mode:  Direct titration
Titrant:  0.1 N iodine VS
Endpoint detection:  Visual
Blank:  100 mL of water and 25 mL of 2 N sulfuric acid. Add 3 mL of starch TS.
Analysis:  Dissolve the Sample in a mixture of 100 mL of water and 25 mL of 2 N sulfuric acid. Add 3 mL of starch TS, and titrate immediately with Titrant until a persistent violet-blue color is obtained.
Calculate the percentage of ascorbic acid (C6H8O6) in the portion of Ascorbic Acid taken:
Result = [(V B) × N × F × 100]/W
V== sample titrant volume (mL)
B== blank titrant volume (mL)
N== titrant normality (mEq/mL)
F== equivalency factor, 88.06 mg/mEq
W== weight of Sample (mg)
Acceptance criteria:  99.0%–100.5%
IMPURITIES
•  Residue on Ignition 281: NMT 0.1%
•  Heavy Metals 231
Sample solution:  1 g in 25 mL of water
Acceptance criteria:  NMT 20 ppm
SPECIFIC TESTS
•  Optical Rotation, Specific Rotation 781S
Sample solution:  100 mg/mL in carbon dioxide-free water. Perform the test immediately after preparation of the Sample solution.
Acceptance criteria:  +20.5 to +21.5
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight, light-resistant containers.
•  USP Reference Standards 11
USP Ascorbic Acid RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Huy T. Dinh, M.S.
Scientific Liaison
1-301-816-8594
(DS2010) Monographs - Dietary Supplements
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 2242