Threonine

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

Threonine contains NLT 98.5% and NMT 101.5% of L-threonine (C₄H₉NO₃), calculated on the dried basis.

2 IDENTIFICATION

A. SPECTROSCOPIC IDENTIFICATION TESTS 〈197〉 , Infrared Spectroscopy : 197K

3 ASSAY

PROCEDURE

Sample: 110 mg of Threonine

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 the Titrant. Perform the Blank determination.

Calculate the percentage of threonine (C₄H₉NO₃) in the Sample taken:

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

V_S = Titrant volume consumed by the Sample (mL)

V_B = Titrant volume consumed by the Blank (mL)

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

F = equivalency factor, 119.1 mg/mEq

W = Sample weight (mg)

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

4 IMPURITIES

RESIDUE ON IGNITION 〈281〉: NMT 0.4%

CHLORIDE AND SULFATE, Chloride〈221〉

Standard solution: 0.50 mL of 0.020 N hydrochloric acid Sample: 0.73 g of Threonine

Acceptance criteria: NMT 0.05%

CHLORIDE AND SULFATE, Sulfate〈221〉

Standard solution: 0.10 mL of 0.020 N sulfuric acid Sample: 0.33 g of Threonine

Acceptance criteria: NMT 0.03% Change to read:

IRON 〈241〉 , Procedures, Procedure 1 (CN 1-J  -2023) : NMT 30 ppm

RELATED COMPOUNDS

Diluent: Hydrochloric acid and water (1:99)

System suitability solution: 0.4 mg/mL each of USP L-Threonine RS and USP L-Proline RS in Diluent

Standard solution: 0.05 mg/mL of USP L-Threonine RS in Diluent. [NOTE—This solution has a concentration equivalent to about 0.5% of that of the Sample solution.]

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

Chromatographic system

(See Chromatography 〈621〉, 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

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

OPTICAL ROTATION, Specific Rotation〈781S〉 Sample solution: 60 mg/mL in water Acceptance criteria: −26.7° to −29.1°

PH 〈791〉

Sample solution: 50 mg/mL solution

Acceptance criteria: 5.0–6.5

LOSS ON DRYING 〈731〉: Dry a sample at 105° for 3 h: it loses NMT 0.2% of its weight.

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers.

USP REFERENCE STANDARDS 〈11〉

USP L-Proline RS USP L-Threonine RS