Identification—
Triturate a quantity of finely powdered Tablets,equivalent to about 100mg of trimethoprim,with 2.5mLof methanol.Add 2.5mLof chloroform,triturate again,and centrifuge.Apply 25µLof this test solution and 25µLof a Standard solution of
USP Trimethoprim RSin a mixture of methanol and chloroform (1:1)containing 20mg per mLto a suitable thin-layer chromatographic plate (see
Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture.Allow the spots to dry,and develop the chromatogram in an unsaturated chamber with a solvent system consisting of a mixture of chloroform,methanol,and ammonium hydroxide (95:7.5:1),until the solvent front has moved approximately 15cm from the origin.Remove the plate from the developing chamber,mark the solvent front,and allow the solvent to evaporate.Locate the spots on the plate by viewing under short-wavelength UVlight:the
RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Dissolution á711ñ—
Medium:
0.01Nhydrochloric acid;900mL.
Apparatus 2:
50rpm.
Time:
45minutes.
Procedure—
Determine the amount of C
14H
18N
4O
3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 271nm of filtered portions of the solution under test,suitably diluted with 0.01Nhydrochloric acid to a concentration of about 20µg per mL,in comparison with a Standard solution having a known concentration of
USP Trimethoprim RSin the same
Medium.
Tolerances—
Not less than 75%(Q)of the labeled amount of C14H18N4O3is dissolved in 45minutes.
Assay—
Mobile phase—
Prepare a filtered and degassed mixture of 1%glacial acetic acid in water (v/v)and acetonitrile (21:4).Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Standard preparation—
Using an accurately weighed quantity of
USP Trimethoprim RS,prepare a solution in methanol having a known concentration of about 0.2mg per mL.
Assay preparation—
Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of trimethoprim,to a 100-mLvolumetric flask,add 50mLof methanol,and sonicate for 5minutes,with intermittent swirling.Dilute with methanol to volume,and mix.Centrifuge,pipet 10mLof the supernatant into a 50-mLvolumetric flask,dilute with methanol to volume,and mix.
Chromatographic system
(see
Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.2-mm ×25-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph five replicate injections of the
Standard preparation,and measure the peak responses as directed for
Procedure:the relative standard deviation is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 10µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the analyte peak.Calculate the quantity,in mg,of C
14H
18N
4O
3,in the portion of Tablets taken by the formula:
500C(rU/rS),
in which
Cis the concentration,in mg per mL,of
USP Trimethoprim RSin the
Standard preparation,and
rUand
rSare the peak responses obtained from the
Assay preparationand the
Standard preparation,respectively.