Agar

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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1 DEFINITION

Agar is the dried, hydrophilic, colloidal substance consisting of the polysaccharides extracted from Gelidium cartilagineum (L.) Gaillon (Fam.Gelidiaceae), Gracilaria confervoides (L.) Greville (Fam. Sphaerococcaceae), and related red algae (Class Rhodophyceae).

2 IDENTIFICATION

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K

B. Iodine TS colors some of the fragments of Agar bluish black, with some areas reddish to violet.

C.

Analysis: Boil a sample with 65 times its weight of water for 10 min, with constant stirring, and subsequently adjust with hot water to a concentration of 1.5%, by weight.

Acceptance criteria: Agar forms a clear liquid that congeals at 30°–39° to form arm resilient gel, which does not liquefy below 80°.

3 IMPURITIES

Change to read:

3.1 Inorganic Impurities

Arsenic 〈211〉, Procedures, Procedure 2 (CN 1-Jun-2023) : NMT 3 ppm

Lead 〈251〉, Procedures, Procedure 1 (CN 1-Jun-2023) : NMT 10 ppm

Articles of Botanical Origin, Acid-Insoluble Ash 〈561〉: NMT 0.5%, on a dry-weight basis

3.2 Organic Impurities

3.2.1 Procedure 1: Limit of Gelatin

Sample solution: Dissolve 1 g of sample in 100 mL of boiling water. Allow to cool to about 50°.

Analysis: To 5 mL of the Sample solution add 2–3 drops of a mixture of 0.2 M potassium dichromate solution and 3 N hydrochloric acid (4:1).

Acceptance criteria: No yellow precipitate is formed.

3.2.2 Procedure 2: Limit of Foreign Starch

Sample solution: Boil 0.10 g in 100 mL of water.

Acceptance criteria: The Sample solution does not, upon cooling, produce a blue color upon the addition of iodine TS.

3.2.3 Procedure 3: Limit of Foreign Insoluble Matter

Sample dispersion: Add sucient water to 7.5 g of sample to make 500 g, boil for 15 min, and read just to the original 500 g.

Analysis: To 100 g of the uniformly mixed Sampledispersion add hot water to make 200 mL. Heat almost to boiling,filter while hot through a tared
ltering crucible. Rinse the container with several portions of hot water, and pass these rinsings through the crucible. Dry the crucible and its contents at 105° to a constant weight.

Acceptance criteria: NMT 15 mg (1.0%) remains in the crucible.

Procedure 4: Articles of Botanical Origin, Foreign Organic Matter 〈561〉: NMT 1.0%

4 SPECIFIC TESTS

Microbial Enumeration Tests〈61〉 and Tests for Specified Microorganisms 〈62〉: The total aerobic microbial count does not exceed 103cfu/g, and the total combined molds and yeasts count does not exceed 102cfu/g. It meets the requirements of the tests for absence of Salmonella species and Escherichia coli.

Water Determination, Method III 〈921〉

Analysis: If necessary, cut a sample into pieces from a 2- to 5-mm square, and dry at 105° for 5 h.

Acceptance criteria: The sample loses NMT 20.0% of its weight.

Articles of Botanical Origin, Total Ash 〈561〉: NMT 6.5%, on a dry-weight basis

Water Absorption

Sample: 5.0 g

Analysis: Place the Sample in a 100-mL graduated cylinder, fill to the mark with water, mix, and allow to stand at 25° for 24 h. Pour the contents of the cylinder through moistened glass wool, allowing the water to drain into a second 100-mL graduated cylinder.

Acceptance criteria: NMT 75 mL of water is obtained.

Botanic Characteristics

Agar: Usually occurs in bundles consisting of thin, membranous, agglutinated strips or in cut, aked, or granulated forms. It may be colored weak yellowish orange, yellowish gray to pale yellow, or colorless. It is tough when damp, brittle when dry.

Histology: When mounted in water, Agar appears granular and somewhat lamentous; a few fragments of the spicules of sponges and a few frustules of diatoms may be present. In Japanese Agar, the frustules of Arachnoidiscus ehrenbergii Baillon often occur, being disk-shaped and 100–300 μm in diameter.

Powdered agar: White to yellowish white or pale yellow; in chloral hydrate TS, its fragments are transparent, more or less granular, striated, and angular, and occasionally they contain frustules of diatoms.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers. No storage requirements are specied.

USP Reference Standards 〈11〉

USP Agar RS