Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

Standard preparation— Dissolve an accurately weighed quantity of USP Pentobarbital RSin freshly prepared dilute ammonium hydroxide (1in 20)to obtain a solution having a known concentration of about 10µg of pentobarbital per mL.The concentration of pentobarbital,multiplied by 1.097,represents the equivalent amount of pentobarbital sodium.

Procedure— Determine the amount of C11H17N2NaO3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 240nm on filtered portions of the solution under test,suitably diluted with freshly prepared dilute ammonium hydroxide (1in 20),in comparison with the Standard preparation.

Tolerances— Not less than 75%(Q)of the labeled amount of C11H17N2NaO3is dissolved in 45minutes.

Procedure for content uniformity— Transfer the contents of 1Capsule to a 250-mLvolumetric flask,with the aid of about 5mLof alcohol.Add 10mLof freshly prepared dilute ammonium hydroxide (1in 200),and without delay dilute with the same solution to volume.Mix,filter if necessary,and discard the first 20mLof the filtrate.Dilute a portion of the clear solution with dilute ammonium hydroxide (1in 200)to obtain a solution having a concentration of about 10µg of pentobarbital sodium per mL.Dissolve a suitable quantity of USP Pentobarbital RSin dilute ammonium hydroxide (1in 200)to obtain a Standard solution having a known concentration of about 10µg per mL.Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 240nm,with a suitable spectrophotometer,using dilute ammonium hydroxide (1in 200)as the blank.Calculate the quantity,in mg,of C11H17N2NaO3in the Capsule taken by the formula: in which Tis the labeled quantity,in mg,of pentobarbital sodium in the Capsule,CUis the concentration,in µg per mL,of pentobarbital sodium in the solution from the Capsule contents,on the basis of the labeled quantity per Capsule and the extent of dilution,CSis the concentration,in µg per mL,of USP Pentobarbital RSin the Standard solution,and AUand ASare the absorbances of the solution from the Capsule contents and the Standard solution,respectively.

Internal standard— n-Tricosane.

Internal standard solution— Dissolve an accurately weighed quantity of n-tricosane in chloroform,and quantitatively dilute with chloroform to obtain a solution having a known concentration of about 0.4mg per mL.

Standard preparation— Dissolve accurately weighed quantities of USP Pentobarbital RSand n-tricosane in chloroform,and quantitatively dilute with chloroform to obtain a solution that contains,in each mL,known amounts of about 0.9mg of USP Pentobarbital RSand about 0.4mg of n-tricosane.

Assay preparation— Weigh not less than 20Capsules,and transfer the contents as completely as possible to a suitable container.Remove any residual powder from the empty capsules with the aid of a current of air,and weigh the capsule shells,determining the weight of the contents by difference.Mix the contents of the Capsules,transfer an accurately weighed portion of the powder,equivalent to about 50mg of pentobarbital sodium,to a separator.Add 15mLof water and 1mLof hydrochloric acid,and extract with five 25-mLportions of chloroform.Filter the extracts through about 15g of anhydrous sodium sulfate that is supported on a funnel by a small pledget of glass wool.Collect the combined filtrate in a 100-mLvolumetric flask,wash the sodium sulfate with 15mLof chloroform,collecting the washing with the filtrate,dilute with chloroform to volume,and mix.Combine 2.0mLof this solution with 1.0mLof Internal standard solutionin a suitable container,and reduce the volume to about 1mLby evaporation,with the aid of a stream of dry nitrogen,at room temperature.

Chromatographic systemandSystem suitability— Proceed as directed for Chromatographic Systemand System Suitabilityunder Barbiturate Assay á361ñ,the resolution,R,between pentobarbital and n-tricosane being not less than 2.3.[NOTE—Relative retention times are,approximately,0.5for n-tricosane barbital and 1.0for pentobarbital.]

Procedure— Proceed as directed for Procedureunder Barbiturate Assay á361ñ.Calculate the quantity,in mg,of C11H17N2NaO3in the portion of Capsules taken by the formula: in which 248.25and 226.27are the molecular weights of pentobarbital sodium and pentobarbital,respectively.