0.1 M Phosphate buffer solution— Prepare as directed in the Assay.

solution A— Dissolve in and dilute with water 14.2 g of anhydrous dibasic sodium phosphate to 1000.0 mL.

solution B— Dissolve in and dilute with water 6.8 g of monobasic potassium phosphate to 500.0 mL.

solution C— Mix 1000 mL of Solution A with 500 mL of Solution B. Verify a pH of 7.0 ± 0.1.

Dilute phosphoric acid solution— Dilute phosphoric acid with water (1 in 10), and mix.

0.1 M Disodium ethylenediaminetetraacetate (EDTA)— Transfer about 3.72 g of disodium ethylenediaminetetraacetate into a 100-mL volumetric flask. Dissolve in and dilute with water to volume, and mix.

0.1% Tetramethylammonium hydroxide solution— Dilute 20 mL of tetramethylammonium hydroxide (10% in water) with water to make 2000 mL, and mix. Adjust with Dilute phosphoric acid solution to a pH of 5.5 ± 0.1.

Mobile phase A— Transfer 0.4 mL of 0.1 M EDTA to 1000 mL of 0.1% Tetramethylammonium hydroxide solution, and mix.

Mobile phase B— Mix 250 mL of 0.1% Tetramethylammonium hydroxide solution, 150 mL of acetonitrile, and 100 mL of methanol. Add 0.2 mL of 0.1 M EDTA, and mix.

Mobile phase— Use variable mixtures of Mobile phase A and Mobile phase B as directed in the Chromatographic system.

Standard solution 1— Dissolve an appropriate amount of USP Cefdinir RS in 0.1 M Phosphate buffer solution (Solution C) to obtain a solution having a known concentration of about 0.75 mg per mL of USP Cefdinir RS. Dilute with 0.1% Tetramethyl ammonium hydroxide solution an appropriate amount of this solution, stepwise, if necessary, to obtain a solution having a known concentration of about 15 µg per mL.

Standard solution 2— Dissolve an appropriate quantity of USP Cefdinir Related Compound A RS in 0.1% Tetramethylammonium hydroxide solution to obtain a solution having a known concentration of about 0.04 mg per mL.

Standard solution 3— Dissolve an appropriate quantity of USP Cefdinir Related Compound B RS in 0.1 M Phosphate buffer solution to obtain a solution having a known concentration of about 0.04 mg per mL.

Resolution solution— Transfer about 37.5 mg of accurately weighed USP Cefdinir RS into a 25-mL volumetric flask. Add about 10 mL of 0.1 M Phosphate buffer solution. Add 5.0 mL of each of Standard solution 2 and Standard solution 3, and dilute with 0.1% Tetramethylammonium hydroxide solution to volume.

Test solution— Transfer a volume of constituted Oral Suspension equivalent to about 150 mg of Cefdinir into a 100-mL volumetric flask. Dissolve in 30 mL of 0.1 M Phosphate buffer solution (Solution C), and dilute with 0.1% Tetramethylammonium hydroxide solution to volume.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 150-mm column that contains 5-µm packing L1. The Test solution is maintained at a temperature of 4 ± 3, and the column temperature is maintained at 40 ± 0.5. The flow rate is about 1 mL per minute. The chromatograph is programmed as follows for a run time of about 60 minutes.

Procedure— Separately inject equal volumes (about 10 µL) of the Resolution solution, Standard solution 1, and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses: the resolution between the cefdinir peak and the third peak of cefdinir related compound A is greater than 1.5; the tailing factor of cefdinir related compound B is not more than 1.5; and the relative standard deviation for the cefdinir peak response in replicate injections of Standard solution 1 is not more than 2.0%. The approximate relative retention times and the relative response factors for each of the related compounds compared to cefdinir are given in Table 1. Calculate the percentage of individual specified and unspecified impurities in the portion of Oral Suspension taken by the formula: in which F is the relative response factor for each impurity, as mentioned in Table 1; CS is the concentration, in mg per mL, of USP Cefdinir RS in Standard solution 1; CU is the concentration, in mg per mL, of Cefdinir in the Test solution; rU is the peak response of each impurity obtained from the Test solution; and rS is the peak response of cefdinir obtained from Standard solution 1. The specified and unspecified impurities meet the limits specified in Table 1.

100(CS / CU)(rU / rS)