Identification—
Dissolve about 35 mg of
USP Sulfadiazine RS in 4 mL of ammonium hydroxide, add 16 mL of methanol, and mix to obtain the Standard solution. Transfer a quantity of Cream, equivalent to about 50 mg of silver sulfadiazine, to a stoppered, 50-mL conical flask, add 4 mL of ammonium hydroxide, and mix until a smooth paste has been obtained. Add 16 mL of methanol, shake for 5 minutes, and filter to obtain the test solution: the test solution so obtained responds to the
Thin-layer Chromatographic Identification Test 
201
, a mixture of chloroform, methanol, and ammonium hydroxide (7:4:1) being used as the developing solvent.
[NOTE—Prepare the developing solvent by first mixing the chloroform and methanol, and then adding the ammonium hydroxide.
]
Microbial limits 61—
It meets the requirements of the tests for absence of
Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella species, and
Escherichia coli and the total count does not exceed 23 cfu per g. It meets also the requirements for
Total Combined Molds and Yeasts Count, fewer than 10 cfu per g being found.
Assay—
Mobile phase
and Diluting solution—Proceed as directed in the Assay under Silver Sulfadiazine.
Internal standard solution—
Dissolve an accurately weighed quantity of sulfamerazine in Diluting solution, and dilute quantitatively, and stepwise if necessary, with Diluting solution to obtain a solution having a known concentration of about 2 mg per mL.
Standard stock solution—
Dissolve an accurately weighed quantity of
USP Silver Sulfadiazine RS in
Diluting solution to obtain a solution having a known concentration of about 1 mg per mL.
Standard preparation 1—
Pipet 10.0 mL of the
Standard stock solution into a 50-mL test tube. Add 20 mL of alcohol and 5.0 mL of the
Internal standard solution, and mix.
Standard preparation 2—
Pipet 2.0 mL of Standard preparation 1 into a 50-mL test tube. Add 40 mL of Mobile phase, and mix.
Assay preparation—
Transfer an accurately weighed portion of Cream, equivalent to about 10 mg of silver sulfadiazine, to a 50-mL round-bottom centrifuge tube. Add about 30 mL of methanol, tightly seal the tube with a cap containing an inert liner, and mix, using a vortex mixer, for about 15 seconds. Centrifuge for 15 minutes. Aspirate, and discard the methanol.
[NOTE—Care should be taken to avoid aspirating any of the residue.
] Transfer 5.0 mL of the
Internal standard solution into the tube, and add 20 mL of alcohol. Replace the cap, and mix. Heat in a water bath at 60
, with periodic mixing, for 15 minutes to melt and disperse the Cream. While the mixture is still hot, transfer 10.0 mL of
Diluting solution to the tube, mix, and cool to room temperature. Transfer 2.0 mL of this solution to another tube, add 40 mL of
Mobile phase, mix, and filter.
Chromatographic system—
Proceed as directed in the Assay under Silver Sulfadiazine. Chromatograph replicate injections of Standard preparation 2, and record the peak responses as directed for Procedure: the resolution, R, between sulfadiazine and sulfamerazine is not less than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of
Standard preparation 2 and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of silver sulfadiazine in the portion of Cream taken by the formula:
10C(RU / RS),
in which
C is the concentration, in mg per mL, of
USP Silver Sulfadiazine RS in the
Standard stock solution; and
RU and
RS are the relative peak response ratios obtained from the
Assay preparation and
Standard preparation 2, respectively.
