Valine

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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C₅H₁₁NO₂  117.15

l-Valine CAS RN®: 72-18-4; UNII: HG18B9YRS7.

1 DEFINITION

Valine contains NLT 98.5% and NMT 101.5% of l-valine (C₅H₁₁NO₂), calculated on the dried basis.

2 IDENTIFICATION

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

3 ASSAY

3.1 Procedure

Sample: 110 mg of Valine

Blank: Mix 3 mL of formic acid and 50 mL of glacial acetic acid.

Titrimetric system

• (See Titrimetry 〈541〉.)
• Mode: Direct titration
• Titrant: 0.1 N perchloric acid VS
• Endpoint detection: Potentiometric

Analysis: Dissolve the Sample in 3 mL of formic acid and 50 mL of glacial acetic acid. Titrate with Titrant. Perform the blank determination.

Calculate the percentage of valine (C₅H₁₁NO₂) in the portion of Valine taken:

Result = {[(V_S − V_B) × N_A × F]/W} × 100

V_S = Titrant volume consumed by the Sample (mL)

V_B = Titrant volume consumed by the Blank (mL)

N_A = actual normality of the Titrant (mEq/mL)

F = equivalency factor, 117.2 mg/mEq

W = Sample weight (mg)

Acceptance criteria: 98.5%–101.5% on the dried basis

4 IMPURITIES

4.1 Residue on Ignition 〈281〉: NMT 0.1%

4.2 Chloride and Sulfate 〈221〉, Chloride

Standard solution: 0.50 mL of 0.020 N hydrochloric acid

Sample: 0.73 g of Valine

Acceptance criteria: NMT 0.05%

4.3 Chloride and Sulfate 〈221〉, Sulfate

Standard solution: 0.10 mL of 0.020 N sulfuric acid

Sample: 0.33 g of Valine

Acceptance criteria: NMT 0.03%

Change to read:

4.4 Iron 〈241〉, Procedures, Procedure 1: NMT 30 ppm

4.5 Related Compounds

System suitability solution: 0.4 mg/mL each of USP l-Valine RS and USP l-Phenylalanine RS in 0.1 N hydrochloric acid

Standard solution: 0.05 mg/mL of USP l-Valine RS in 0.1 N hydrochloric acid. [Note-This solution has a concentration equivalent to 0.5% of the Sample solution.]

Sample solution: 10 mg/mL of Valine in 2 N hydrochloric acid

Chromatographic system

• (See Chromatography 〈621〉, General Procedures, Thin-Layer Chromatography.)
• Mode: TLC
• Adsorbent: 0.25-mm layer of chromatographic silica gel mixture
• Application volume: 5 µL
• Developing solvent system: Butyl alcohol, glacial acetic acid, and water (3:1:1)
• Spray reagent: 2 mg/mL of ninhydrin in a mixture of butyl alcohol and 2 N acetic acid (95:5)

System suitability

• Sample: System suitability solution
• Suitability requirements: The chromatogram of the System suitability solution exhibits two clearly separated spots.

Analysis

Samples: System suitability solution, Standard solution, and Sample solution

After air-drying the plate, spray with Spray reagent, and heat between 100° and 105° for 15 min. Examine the plate under white light.

Acceptance criteria: Any secondary spot of the Sample solution is not larger or more intense than the principal spot of the Standard solution.

• Individual impurities: NMT 0.5%
• Total impurities: NMT 2.0%

5 SPECIFIC TESTS

5.1 Optical Rotation 〈781S〉, Procedures, Specific Rotation

Sample solution: 80 mg/mL in 6 N hydrochloric acid

Acceptance criteria: +26.6° to +28.8°

5.2 pH 〈791〉

Sample solution: 50 mg/mL

Acceptance criteria: 5.5–7.0

5.3 Loss on Drying 〈731〉

Analysis: Dry at 105° for 3 h.

Acceptance criteria: NMT 0.3%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP l-Phenylalanine RS

USP l-Valine RS