for oral suspension packaged in single-unit containers: meets the requirements.

for oral suspension packaged in multiple-unit containers: meets the requirements.

Internal standard solution— Dissolve a suitable quantity of androsterone in alcohol to obtain a solution having a final concentration of about 10 mg per mL.

Standard preparation— Transfer about 100 mg of USP Primidone RS, accurately weighed, to a 100-mL volumetric flask, add 65 mL of alcohol, and boil for 1 hour. Allow to cool to ambient temperature, add 10.0 mL of Internal standard solution, dilute with alcohol to volume, mix, and filter.

Assay preparation— Transfer an accurately weighed quantity of well-mixed Oral Suspension, equivalent to about 50 mg of primidone, to a 50-mL volumetric flask; add 35 mL of alcohol; and boil for 1 hour. Allow to cool to ambient temperature, add 5.0 mL of Internal standard solution, dilute with alcohol to volume, mix, and filter.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 4.0-mm × 120-cm column packed with 10% liquid phase G3 on support S1AB. Helium is used as the carrier gas at a flow rate of about 40 mL per minute. The detector and injection port temperatures are maintained at about 310, and the column temperature is maintained at about 260. Chromatograph three 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 factor between primidone and androsterone is not less than 1.5.

Procedure— Separately inject equal volumes (about 3 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 are about 0.8 for primidone and 1.0 for androsterone. Calculate the quantity, in mg, of primidone (C12H14N2O2) in each mL of the Oral Suspension taken by the formula: in which D is the density, in g per mL, of the Oral Suspension; WS is the weight, in mg, of the Standard used; WU is the weight, in mg, of Oral Suspension taken; and RU and RS are the relative response factors obtained from the Assay preparation and the Standard preparation, respectively.