Erythorbic Acid - Definition, Identification, Impurities - USP 2025

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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o-Araboascorbic acid;

d-Erythro-hex-2-enoic acid delta-lactone;

Isoascorbic acid, d-isoascorbic acid

CAS RN®: 89-65-6.

1 DEFINITION

Erythorbic Acid contains NLT 99.0% and NMT 100.5% of C₆H₈O₆, calculated on the dried basis.

IDENTIFICATION

Change to read:

• A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020)

• B.

Sample solution: 20 mg/mL of Erythorbic Acid and water

Analysis: To 2 mL of Sample solution add a few drops of sodium nitroferricyanide TS and then add 1 mL of 0.1 N sodium hydroxide.

Acceptance criteria: A transient blue color immediately appears.

• C.

Analysis: Dissolve about 15 mg of Erythorbic Acid in 15 mL of trichloroacetic acid (1:20). Add about 200 mg of activated charcoal, and shake the mixture vigorously for 1 min. Pass through a small fluted filter, refilter if necessary to obtain a clear filtrate, agitate the mixture until the pyrrole is dissolved, and heat in a water bath at 50°.

Acceptance criteria: A blue color appears.

2 ASSAY

• Procedure

Sample: 400 mg

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.1 N iodine VS

Endpoint detection: Colorimetric

Analysis

Dissolve the Sample in a mixture of 100 mL of recently boiled and cooled water and 25 mL of 2 N sulfuric acid. Add 3 mL of starch TS, and titrate at once with 0.1 N iodine VS. Perform a blank determination.

Calculate the percentage of erythorbic acid (C₆H₈O₆) in the Sample taken:

Result = [(V − B) × N × F × 100] / W

V = Titrant volume consumed by the Sample (mL)

B = Titrant volume consumed by the Blank (mL)

N = Titrant actual normality (mEq/mL)

F = equivalency factor, 88.06 mg/mEq

W = weight of the Sample (mg)

Acceptance criteria: 99.0%–100.5% on the dried basis

3 IMPURITIES

• Residue on Ignition 〈281〉: NMT 0.3%

Limit of Lead

[Note—Select reagents having as low a lead content as practicable, and store all solutions in borosilicate glass containers. Rinse all glassware thoroughly with warm 8 N nitric acid followed by deionized water.]

Standard stock solution:

Dissolve 160 mg of lead nitrate in 100 mL of water containing 1 mL of nitric acid. Dilute with water to 1000 mL.

On the day of use, transfer 10.0 mL of the above solution to a 100-mL volumetric flask, and dilute with water to volume.

Each mL of this solution contains the equivalent of about 10 µg of lead.

[Note—Prepare the Standard solutions on the day of use.]

Standard solutions:

Standard solution A: 1 µg/mL of lead from the Standard stock solution

Standard solution B: 2 µg/mL of lead from the Standard stock solution

Standard solution C: 5 µg/mL of lead from the Standard stock solution

Sample solution:

Transfer a weighed portion of about 10 g of Erythorbic Acid to an evaporating dish. Add 5 mL of 25% sulfuric acid, and distribute the sulfuric acid uniformly through the sample. Within a hood, place the dish on a steam bath to evaporate most of the water.

Place the dish on a burner, and slowly pre-ash the sample by expelling most of the sulfuric acid.

Place the dish in a muffle furnace at 525°, and ash the sample until the residue appears free from carbon.

Cool, and cautiously wash down the inside of the evaporation dish with water. Add 5 mL of 1 N hydrochloric acid.

Place the dish on a steam bath, and evaporate to dryness.

Add 1.0 mL of 3 N hydrochloric acid and approximately 5 mL of water, and heat briefly on a steam bath to dissolve any residue.

Transfer quantitatively to a 10-mL volumetric flask, and dilute with water to volume.

Blank:

Prepare identically as the Sample solution, but without Erythorbic Acid.

Instrumental conditions

(See Atomic Absorption Spectroscopy 〈852〉.)

Mode: Atomic absorption

Lamp: Lead electrodeless discharge

Flame: Air–acetylene

Analytical wavelength: 283.3 nm

Slit width: 0.7 nm

Standard curve

Samples: Standard solution A, Standard solution B, Standard solution C, and Blank

Plot: Corrected absorbance values versus concentration (µg/mL).

[Note—Determine the corrected absorbance by subtracting the Blank.]

Analysis

Sample: Sample solution

From the Standard curve, determine the lead concentration in the Sample solution. Calculate the lead content, in ppm, in the portion of Erythorbic Acid taken:

Result = V × C_S / W

V = volume of the Sample solution (mL)

C_S = concentration of lead in the Sample solution (µg/mL)

W = weight of Erythorbic Acid in the Sample solution (g)

Acceptance criteria: NMT 10 ppm

4 SPECIFIC TESTS

• Optical Rotation, Specific Rotation 〈781S〉: −16.5° to −18.0°

Sample solution: 100 mg/mL in water

• Loss on Drying 〈731〉:

Dry a sample in a vacuum over silica gel for 3 h: it loses NMT 0.4% of its weight.

5 ADDITIONAL REQUIREMENTS

• Packaging and Storage: Preserve in tight, light-resistant containers.

• USP Reference Standards 〈11〉

USP Erythorbic Acid RS