» Methionine contains not less than 98.5 percent and not more than 101.5 percent of C5H11NO2S, as l-methionine, calculated on the dried basis.
Packaging and storage Preserve in well-closed containers.
Specific rotation 781S: between +22.4 and +24.7.
Test solution: 20 mg per mL, in 6 N hydrochloric acid.
pH 791: between 5.6 and 6.1 in a solution (1 in 100).
Loss on drying 731 Dry it at 105 for 3 hours: it loses not more than 0.3% of its weight.
Residue on ignition 281: not more than 0.4%.
Chloride 221 A 0.73-g portion shows no more chloride than corresponds to 0.50 mL of 0.020 N hydrochloric acid (0.05%).
Sulfate 221 A 0.33-g portion shows no more sulfate than corresponds to 0.10 mL of 0.020 N sulfuric acid (0.03%).
Iron 241: 0.003%.
Heavy metals, Method I 231: 0.0015%.
Adsorbent: 0.25-mm layer of chromatographic silica gel mixture.
Test solution Dissolve an accurately weighed quantity of Methionine in 0.3 M hydrochloric acid to obtain a solution having a concentration of 10 mg per mL. Apply 5 µL.
Standard solution Dissolve an accurately weighed quantity of USP l-Methionine RS in 0.3 M hydrochloric acid to obtain a solution having a known concentration of about 0.05 mg per mL. Apply 5 µL. [noteThis solution has a concentration equivalent to about 0.5% of that of the Test solution.]
System suitability solution Prepare a solution in 0.3 N hydrochloric acid containing 0.4 mg each of USP l-Methionine RS and USP l-Serine RS per mL. Apply 5 µL.
Spray reagent Dissolve 0.2 g of ninhydrin in 100 mL of a mixture of butyl alcohol and 2 N acetic acid (95:5).
Developing solvent system Prepare a mixture of butyl alcohol, glacial acetic acid, and water (60:20:20).
Procedure Proceed as directed for Thin-Layer Chromatography under Chromatography 621. After air-drying the plate, spray with Spray reagent, and heat between 100 and 105 for about 15 minutes. Examine the plate under white light. The chromatogram obtained from the System suitability solution exhibits two clearly separated spots. Any secondary spot in the chromatogram obtained from the Test solution is not larger or more intense than the principal spot in the chromatogram obtained from the Standard solution: not more than 0.5% of any individual impurity is found; and not more than 2.0% of total impurities is found.
Assay Transfer about 140 mg of Methionine, accurately weighed, to a 125-mL flask, dissolve in a mixture of 3 mL of formic acid and 50 mL of glacial acetic acid, and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 14.92 mg of C5H11NO2S.
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USP32NF27 Page 2924
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.