Ascorbic Acid

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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C₆H₈O₆  176.12

L-Ascorbic acid CAS RN: 50-81-7.

1 DEFINITION

Ascorbic Acid contains NLT 99.0% and NMT 100.5% of C₆H₈O₆.

2 IDENTIFICATION

Change to read:

A. ASPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197K (CN 1-MAY-2020)

B. A 20-mg/mL solution reduces alkaline cupric tartrate TS slowly at room temperature but more readily upon heating.

3 ASSAY

3.1 PROCEDURE

Sample: 400 mg of Ascorbic Acid

Titrimetric system (See Titrimetry (541).)

Mode: Direct titration

Titrant: 0.1 N iodine VS

Endpoint detection: Visual

Blank: 100 mL of water and 25 mL of 2N 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%

4 IMPURITIES

RESIDUE ON IGNITION (281): NMT 0.1%

5 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°

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight, light-resistant containers.

USP REFERENCE STANDARDS (11).

USP Ascorbic Acid RS