A: Place 10mLof Oral Solution in a separator containing 20mLof water,add 5mLof 1Nsodium hydroxide,and extract with two 10-mLportions of chloroform,discarding the chloroform extracts.Add 5mLof 3Nhydrochloric acid,and extract with two 25-mLportions of chloroform,filtering the extracts through paper into a beaker.Remove the chloroform by evaporation on a steam bath,and dry the residue at 105for 2hours:the residue so obtained meets the requirements for Identificationtest Aunder Phenobarbital.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,both relative to the internal standard,as obtained in the Assay.

pH4.5Buffer solution,Mobile phase,andChromatographic system— Prepare as directed in the Assayunder Phenobarbital.

Diluent— Prepare a mixture of methanol and pH4.5Buffer solution(2:1).

Internal standard solution— Dissolve a sufficient quantity of caffeine in Diluentto obtain a solution having a concentration of about 1.7mg per mL.

Standard preparation— Transfer about 33mg of USP Phenobarbital RS,accurately weighed,to a 25-mLvolumetric flask containing 2.0mLof Internal standard solution.Dilute with Diluentto volume,and mix.

Assay preparation— Transfer a quantity of Oral Solution,equivalent to about 33mg of phenobarbital,to a 25-mLvolumetric flask containing 2.0mLof Internal standard solution.Dilute with Diluentto volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Phenobarbital.Calculate the quantity,in mg,of phenobarbital (C12H12N2O3)in the portion of the Oral Solution taken by the formula: in which the terms are as defined therein.