A: Transfer a volume of Injection, equivalent to about 250 mg of phenytoin sodium, to a separator containing 25 mL of water. Extract, in the order listed, with 50-, 30-, and 30-mL portions of ethyl acetate. Wash each extract with two 20-mL portions of sodium acetate solution (1 in 100). Evaporate the combined ethyl acetate extracts, and dry the residue of phenytoin at 105 to constant weight: the IR absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a potassium bromide dispersion of USP Phenytoin RS.

B: It responds to the flame test for Sodium 191.

Internal standard solution— Pipet 8 mL of methanol and 20 mL of ethylene glycol into a 100-mL volumetric flask, dilute with water to volume, and mix.

Alcohol solution— Pipet 6 mL of dehydrated alcohol into a 100-mL volumetric flask, dilute with water to volume, and mix.

Propylene glycol solution— Pipet 20 mL of propylene glycol into a 100-mL volumetric flask, dilute with water to volume, and mix.

Standard preparation— Pipet 10 mL each of Internal standard solution, Alcohol solution, and Propylene glycol solution into a 100-mL volumetric flask, dilute with water to volume, and mix.

Test preparation— Pipet 5 mL of Injection and 10 mL of Internal standard solution into a 100-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The gas chromatograph is equipped with a flame-ionization detector and a 1.8-m × 2.0-mm (ID) glass column packed with 50- to 80-mesh silanized packing S3. The column is maintained at a temperature of 140 for 3 minutes, programmed at a rate of 6 per minute to a temperature of 190, and maintained at 190 for 6 minutes, helium being used as the carrier gas at a flow rate of about 40 mL per minute. The injection port and detector are maintained at a temperature of 200. Chromatograph five replicate injections of the Standard preparation, and record the chromatograms: the resolution, R, between methanol and alcohol is not less than 2.0, the resolution, R, between ethylene glycol and propylene glycol is not less than 3.0, and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 2 µL) of the Standard preparation and the Test preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The order of elution is methanol, alcohol, ethylene glycol, and propylene glycol in order of increasing retention time: the relative retentions are about 1.0 for methanol and 2.2 for alcohol with respect to methanol and alcohol peaks, and about 1.0 for ethylene glycol and 1.4 for propylene glycol with respect to the ethylene glycol and propylene glycol peaks. Calculate the relative response ratio for the alcohol peak with respect to the methanol peak and for the propylene glycol peak with respect to the ethylene glycol peak. Calculate the alcohol content, in percentage, taken by the formula: in which RU and RS are the relative response ratios for the methanol and alcohol peaks obtained from the Test preparation and the Standard preparation, respectively. Calculate the propylene glycol content, in percentage, taken by the formula: in which R¢U and R¢S are the relative response ratios for the ethylene glycol and propylene glycol peaks obtained from the Test preparation and the Standard preparation, respectively. The alcohol content is not less than 9.0% and not more than 11.0%, and the propylene glycol content is not less than 37.0% and not more than 43.0%.

(Official January 1, 2007)

Mobile phase— Prepare a suitable degassed and filtered mixture of methanol and water (55:45).

Standard preparation— Dissolve an accurately weighed portion of USP Phenytoin RS in Mobile phase to obtain a solution having a known concentration of about 230 µg per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to 250 mg of phenytoin sodium, to a volumetric flask and dilute quantitatively and stepwise with Mobile phase to obtain a solution having a concentration of about 250 µg of phenytoin sodium per mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph 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 tailing factor is not more than 2.0.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the response for the major peak. Calculate the quantity, in mg, of C15H11N2NaO2 in each mL of the Injection taken by the formula: in which 274.25 and 252.27 are the molecular weights of phenytoin sodium and phenytoin, respectively, C is the concentration, in µg per mL, of USP Phenytoin RS in the Standard preparation, V is the volume, in mL, of Injection taken, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.