Packaging and storage—
Preserve in well-closed containers. Store at 25
, excursions permitted between 15
and 30
.
Identification—
A: Ultraviolet Absorption 
197U
—
Solution—
Transfer about 100 mg of it, accurately weighed, to a 100-mL volumetric flask, dissolve in 25 mL of alcohol, dilute with 0.1 N sodium hydroxide to volume, and mix.
Medium—
Dilute the Solution quantitatively and stepwise with 0.1 N sodium hydroxide to obtain a solution containing a known concentration of about 20 µg per mL.
Absorptivity, at about 287 nm, calculated on the anhydrous basis, is between 83.0% and 86.4% of
USP Trimethoprim RS.
B:
It responds to the tests for
Sulfate 191.
Chromatographic purity—
Adsorbent:
0.25-mm layer of chromatographic silica gel mixture.
Diluent—
Prepare a mixture of chloroform and methanol (9:1).
Test solution—
Transfer about 20 mg of Trimethoprim Sulfate, accurately weighed, to a 10-mL volumetric flask, add 4 mL of glacial acetic acid, and swirl to dissolve. Dilute with Diluent to volume, and mix.
Standard solution—
Dissolve an accurately weighed quantity of
USP Trimethoprim RS in
Diluent. Dilute an accurately measured volume of this solution quantitatively, and stepwise if necessary, with
Diluent to obtain a solution having a known concentration of 0.02 mg per mL.
Application volume:
10 µL.
Developing solvent system:
a mixture of chloroform, methanol, and 6 N ammonium hydroxide (95:7.5:1).
Procedure—
Proceed as directed for
Thin-Layer Chromatography under
Chromatography 621. Spray the plate with a freshly prepared mixture of 1.9 g of ferric chloride in 20 mL of water and 0.5 g of potassium ferricyanide in 10 mL of water. Compare the intensities of any secondary spots observed in the chromatogram of the
Test solution with that of the principal spot in the chromatogram of the
Standard solution: no secondary spot in the chromatogram obtained from the
Test solution is larger or more intense than the principal spot obtained from the
Standard solution (0.1%); and the sum of the intensities of the secondary spots obtained from the
Test solution corresponds to not more than 0.5%.
;)
