Methimazole
;)
2H-Imidazole-2-thione,1,3-dihydro-1-methyl-.
1-Methylimidazole-2-thiol [60-56-0].
»Methimazole contains not less than 98.0percent and not more than 101.0percent of C4H6N2S,calculated on the dried basis.
Packaging and storage—
Preserve in well-closed,light-resistant containers.
Identification—
A:
Infrared Absorption á197Kñ.
B:
Mercuric chloride TSproduces in a solution (1in 200)a white precipitate,but no precipitation is produced by trinitrophenol TS.The solution is colored intensely blue by molybdophosphotungstate TS.
Loss on drying á731ñ—
Dry it at 105
for 2hours:it loses not more than 0.5%of its weight.
for 2hours:it loses not more than 0.5%of its weight.
Residue on ignition á281ñ:
not more than 0.1%.
Selenium á291ñ:
0.003%,a 200-mg specimen being used.
Ordinary impurities á466ñ—
Test solution:
ethyl acetate.
Standard solution:
ethyl acetate.
Eluant:
a mixture of toluene,isopropyl alcohol,and ammonium hydroxide (70:29:1),in a nonequilibrated chamber.
Visualization:
2.
Organic volatile impurities,Method Iá467ñ:
meets the requirements.
Assay—
Dissolve about 250mg of Methimazole,accurately weighed,in 75mLof water.Add from a buret 15mLof 0.1Nsodium hydroxide VS,mix,and add,with agitation,about 30mLof 0.1Nsilver nitrate.Add 1mLof bromothymol blue TS,and continue the titration with the 0.1Nsodium hydroxide VSuntil a permanent,blue-green color is produced.Each mLof 0.1Nsodium hydroxide is equivalent to 11.42mg of C4H6N2S.
Auxiliary Information—
Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1244
Phone Number:1-301-816-8251