Prepare a suitable degassed solution of water, acetonitrile, and glacial acetic acid (86:13:1) such that the relative retention times of sulfadiazine, sulfamerazine, and sulfamethazine are approximately 0.6, 0.8, and 1.0, respectively. (If the retention times are excessive, the concentration of acetonitrile may be increased.)
Transfer 33 mg each of USP Sulfadiazine RS
, USP Sulfamerazine RS
, and USP Sulfamethazine RS
, accurately weighed, to a 100-mL volumetric flask, dissolve in 25 mL of 0.1 N sodium hydroxide, dilute with water to volume, and mix. Pipet 3 mL into a 25-mL volumetric flask, dilute with water to volume, and mix to obtain a Standard preparation
having a known concentration of about 40 µg of each USP Reference Standard per mL.
Determine the specific gravity of the Oral Suspension, using a tared, 50-mL volumetric flask, by weighing 50 mL of Oral Suspension that previously has been shaken in the original container to ensure homogeneity, allowed to stand long enough for entrapped air to rise, and finally inverted carefully just prior to transfer to the volumetric flask. Transfer an accurately weighed quantity of Oral Suspension, well-shaken and free from entrapped air, equivalent to about 100 mg of total sulfapyrimidines, to a 100-mL volumetric flask, add 25 mL of 0.1 N sodium hydroxide, and swirl for several minutes to dissolve the sulfapyrimidines. Dilute with water to volume, and mix. Filter the mixture, discarding the first several mL of the filtrate. Pipet 3 mL of the clear filtrate into a 25-mL volumetric flask, dilute with water to volume, and mix.
Chromatographic system (see Chromatography 621)
The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph five replicate injections of the Standard preparation,
and record the peak responses as directed for Procedure:
the relative standard deviation is not more than 2.0%, and the resolution factors between sulfadiazine and sulfamerazine and between sulfamerazine and sulfamethazine are each not less than 3.0.
Separately inject equal volumes (about 20 µL) of the Standard preparation
and the Assay preparation
into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times for sulfadiazine, sulfamerazine, and sulfamethazine are approximately 0.6, 0.8, and 1.0, respectively. Calculate the quantity, in mg, of sulfadiazine in the portion of Oral Suspension taken by the formula:
0.833C(RU / RS),
in which C
is the concentration, in µg per mL, of USP Sulfadiazine RS
in the Standard preparation;
are the peak responses obtained from the Assay preparation
and the Standard preparation,
respectively. Similarly measure the responses of the sulfamerazine and sulfamethazine peaks, and calculate the quantity, in mg, of each in the portion of Oral Suspension taken.