A: Shake a volume of Oral Suspension,equivalent to about 100mg of phenytoin,with 50mLof a mixture of ether and chloroform (1in 2)in a separator,evaporate the extract to dryness,and dry in vacuum at 105for 4hours:the phenytoin so obtained melts between 292and 299with some decomposition,the procedure for Class Ibeing used (see Melting Range or Temperature á741ñ).

B: Dissolve 50mg of the residue obtained in Identificationtest Ain 50mLof chloroform,with slight warming if necessary.To 5mLof this solution add 0.2mLof a freshly prepared solution of cobaltous acetate in methanol (1in 100)and 1mLof a freshly prepared solution of isopropylamine in methanol (1in 20),and mix:a violet to red-violet color is produced.

Change to read:

0.05M Tris buffer— Dissolve 36.3g of tris(hydroxymethyl)aminomethane and 60g of sodium lauryl sulfate in 6Lof water,adjust with hydrochloric acid to a pHof 7.5±0.05,and degas.

Medium: 0.05M Tris buffer;900mL.

Apparatus 2: 35rpm.

Time: 60minutes.

Dissolution procedure— Shake the sample suspension well,about 100shakes.Using a 5-mLsyringe,collect approximately 5mLof suspension,and record the weight.With the paddles lowered,gently empty the contents of each syringe into the bottom of each vessel containing the Medium.Start rotating the paddles.Reweigh each syringe,and determine the amount of suspension delivered into each vessel.At the end of 60minutes,remove 4mLfrom each vessel,and pass through a 0.45-µm nylon filter presaturated with Medium.USP28

0.02M Sodium phosphate buffer— Dissolve 2.76g of monobasic sodium phosphate in 1Lof water.

Mobile phase— Prepare a filtered and degassed mixture of 0.02M Sodium phosphate buffer,methanol,and acetonitrile (50:27:23),and mix.Adjust with phosphoric acid to a pHof 3.0.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Transfer about 70mg of USP Phenytoin RS,accurately weighed,to a 500-mLvolumetric flask.Dissolve in 15mLof methanol,dilute with Mediumto volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 240-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard solution,and record the responses as directed for Procedure:the column efficiency is not less than 5400theoretical plates;the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the solution under testUSP28into the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C15H12N2O2dissolved.[NOTE—The density of Oral Suspension must be determined and used in calculating the quantity,in mg,of phenytoin dissolved.]

Tolerances— Not less than 80%(Q)of the labeled amount of C15H12N2O2is dissolved in 60minutes.

FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

Mobile phase— Prepare a filtered and degassed mixture of water,methanol,acetonitrile,0.5%triethylamine in water,and 1.74Nacetic acid (191:100:40:1.3:1).Make adjustments if necessary.

Standard preparation— Dissolve an accurately weighed quantity of USP Phenytoin RSin methanol,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.625mg per mL.

Assay preparation— Transfer a quantity of Oral Suspension,equivalent to about 125mg of phenytoin,into a 200-mLvolumetric flask,rinse the pipet with 40mLof methanol,and add the rinsings to the flask.Add about 50mLof Mobile phase,dilute with methanol to volume,mix,sonicate,and filter.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 229-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 1.5;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of phenytoin (C15H12N2O2)in the portion of Oral Suspension taken by the formula: in which Cis the concentration,in mg per mL,of USP Phenytoin RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.