A: Transfer a volume of Injection,equivalent to about 250mg of phenytoin sodium,to a separator containing 25mLof water.Extract,in the order listed,with 50-,30-,and 30-mLportions of ethyl acetate.Wash each extract with two 20-mLportions of sodium acetate solution (1in 100).Evaporate the combined ethyl acetate extracts,and dry the residue of phenytoin at 105to constant weight:the IRabsorption 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 á191ñ.

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

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

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

Standard preparation— Pipet 10mLeach of Internal standard solution,Alcohol solution,and Propylene glycol solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix.

Test preparation— Pipet 5mLof Injection and 10mLof Internal standard solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—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 140for 3minutes,programmed at a rate of 6per minute to a temperature of 190,and maintained at 190for 6minutes,helium being used as the carrier gas at a flow rate of about 40mLper 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 2µL)of the Standard preparationand the Test preparationinto 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 1.0for methanol and 2.2for alcohol with respect to methanol and alcohol peaks,and about 1.0for ethylene glycol and 1.4for 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 RUand RSare the relative response ratios for the methanol and alcohol peaks obtained from the Test preparationand the Standard preparation,respectively.Calculate the propylene glycol content,in percentage,taken by the formula: in which R¢Uand R¢Sare the relative response ratios for the ethylene glycol and propylene glycol peaks obtained from the Test preparationand 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%.

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 RSin Mobile phaseto obtain a solution having a known concentration of about 230µg per mL.

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

Chromatographic system (see Chromatography á621ñ)—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 1.5mLper 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 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the response for the major peak.Calculate the quantity,in mg,of C15H11N2NaO2in each mLof the Injection taken by the formula: in which 274.25and 252.27are the molecular weights of phenytoin sodium and phenytoin,respectively,Cis the concentration,in µg per mL,of USP Phenytoin RSin the Standard preparation,Vis the volume,in mL,of Injection taken,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.