Identification—
Transfer an amount of finely ground Tablets,equivalent to 4mg of trimethoprim,to a 10-mLvolumetric flask,add 8mLof methanol,warm for several minutes on a steam bath with frequent shaking,cool,dilute with methanol to volume,mix,and centrifuge briefly.Apply 5µLeach of this solution,a Standard solution of
USP Trimethoprim RSin methanol containing 0.4mg per mL,and a Standard solution of
USP Sulfamethoxazole RSin methanol containing 2mg per mLto separate points about 3cm from one end of a thin-layer chromatographic plate coated with chromatographic silica gel mixture.Dry the spots in a current of warm air,and develop the plate with a mixture of chloroform,isopropyl alcohol,and diethylamine (6:5:1)in a chamber lined with filter paper.Remove the plate,dry,and examine under short-wavelength UVlight:the trimethoprim and sulfamethoxazole spots from the solution under test have the same
RFvalues as the spots from the corresponding Standard solutions.
Dissolution á711ñ—
Medium:
0.1Nhydrochloric acid;900mL.
Apparatus 2:
75rpm.
Time:
60minutes.
Procedure—
Determine the amounts of sulfamethoxazole (C
10H
11N
3O
3S)and trimethoprim (C
14H
18N
4O
3)dissolved,employing the procedure set forth in the
Assay,making any necessary volumetric adjustments (see
Chromatography á621ñ).Calculate the percentage of each active component dissolved by comparison of the peak responses obtained from a filtered aliquot of the solution under test with the peak responses from the corresponding component obtained from the
Standard preparation.
Tolerances—
Not less than 70%(Q)of the labeled amounts of C10H11N3O3Sand C14H18N4O3is dissolved in 60minutes.
Assay—
Assay preparation—
Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 160mg of sulfamethoxazole,to a 100-mLvolumetric flask.Add about 50mLof methanol and sonicate,with intermittent shaking,for 5minutes.Allow to equilibrate to room temperature,dilute with methanol to volume,mix,and filter.Transfer 5.0mLof the clear filtrate to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.
Procedure—
Separately inject equal volumes (about 20µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantities,in mg,of trimethoprim (C
14H
18N
4O
3)and sulfamethoxazole (C
10H
11N
3O
3S)in the portion of Tablets taken by the formula:
1000C(rU/rS),
in which
Cis the concentration,in mg per mL,of the appropriate USP Reference Standard in the
Standard preparation;and
rUand
rSare the responses of the corresponding analyte obtained from the
Assay preparationand the
Standard preparation,respectively.