Methionine
;)
L-Methionine.
L-Methionine [63-68-3].
»Methionine contains not less than 98.5percent and not more than 101.5percent of C5H11NO2S,as L-methionine,calculated on the dried basis.
Packaging and storage—
Preserve in well-closed containers.
Identification,Infrared Absorption á197Kñ.
Specific rotation á781Sñ:
between +22.4
and +24.7.
and +24.7.
Test solution:
20mg per mL,in 6Nhydrochloric acid.
pHá791ñ:
between 5.6and 6.1in a solution (1in 100).
Loss on drying á731ñ—
Dry it at 105for 3hours:it loses not more than 0.3%of its weight.
for 3hours:it loses not more than 0.3%of its weight.
Residue on ignition á281ñ:
not more than 0.4%.
Chloride á221ñ—
A0.73-g portion shows no more chloride than corresponds to 0.50mLof 0.020Nhydrochloric acid (0.05%).
Sulfate á221ñ—
A0.33-g portion shows no more sulfate than corresponds to 0.10mLof 0.020Nsulfuric acid (0.03%).
Iron á241ñ:
0.003%.
Heavy metals,Method Iá231ñ:
0.0015%.
Chromatographic purity—
Adsorbent:
0.25-mm layer of chromatographic silica gel mixture.
Test solution—
Dissolve an accurately weighed quantity of Methionine in 0.3Mhydrochloric acid to obtain a solution having a concentration of 10mg per mL.Apply 5µL.
Standard solution—
Dissolve an accurately weighed quantity of USPL-Methionine RSin 0.3Mhydrochloric acid to obtain a solution having a known concentration of about 0.05mg per mL.Apply 5µL.[NOTE—This solution has a concentration equivalent to about 0.5%of that of the Test solution.]
System suitability solution—
Prepare a solution in 0.3Nhydrochloric acid containing 0.4mg each of USP L-Methionine RSand USPL-Serine RSper mL.Apply 5µL.
Spray reagent—
Dissolve 0.2g of ninhydrin in 100mLof a mixture of butyl alcohol and 2Nacetic 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 Chromatographyunder Chromatography á621ñ.After air-drying the plate,spray with Spray reagent,and heat between 100and 105for about 15minutes.Examine the plate under white light.The chromatogram obtained from the System suitability solutionexhibits two clearly separated spots.Any secondary spot in the chromatogram obtained from the Test solutionis 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.
and 105for about 15minutes.Examine the plate under white light.The chromatogram obtained from the System suitability solutionexhibits two clearly separated spots.Any secondary spot in the chromatogram obtained from the Test solutionis 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.
Organic volatile impurities,Method Iá467ñ:
meets the requirements.
Assay—
Transfer about 140mg of Methionine,accurately weighed,to a 125-mLflask,dissolve in a mixture of 3mLof formic acid and 50mLof glacial acetic acid,and titrate with 0.1Nperchloric acid VS,determining the endpoint potentiometrically.Perform a blank determination,and make any necessary correction.Each mLof 0.1Nperchloric acid is equivalent to 14.92mg of C5H11NO2S.
Auxiliary Information—
Staff Liaison:Lawrence Evans,III,Ph.D.,Scientist
Expert Committee:(DSN)Dietary Supplements:Non-Botanicals
USP28–NF23Page 1245
Phone Number:1-301-816-8389