A: The retention time ratios of the valproic acid peak to the internal standard peak obtained from the Standard preparationand the Assay preparationas directed in the Assaydo not differ by more than 2.0%.

B: Place a portion of Capsule contents,equivalent to about 250mg of valproic acid,in a separator.Add 20mLof 1Nsodium hydroxide,shake,and allow the layers to separate.Transfer the aqueous layer to a second separator,add 4mLof hydrochloric acid,mix,and extract with 40mLof n-heptane.Filter the n-heptane layer through glass wool into a beaker,and evaporate the solvent completely on a steam bath with the aid of a current of air.Transfer 2drops of the residue to a test tube containing 0.5mLeach of potassium iodide solution (1in 50)and potassium iodate solution (1in 25),and mix:a yellow color is produced.

Medium: a solution containing 5mg per mLof sodium lauryl sulfate in simulated intestinal fluid TS(prepared without the enzyme and with monobasic sodium phosphate instead of monobasic potassium phosphate),adjusted with 5Msodium hydroxide to a pHof 7.5;900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Internal standard solution and Chromatographic system—Proceed as directed in the Assay.

Standard preparation— Prepare a solution of USP Valproic Acid RShaving a concentration similar to that of the solution under test.Transfer 10.0mLto a suitable container.Add about 3.0g of sodium chloride,and mix on a vortex mixer for 5minutes.Add about 1mLof 6Nhydrochloric acid and 5.0mLof Internal standard solution,and shake for 2minutes.Allow the phases to separate,remove the n-heptane layer,and filter.Discard the aqueous layer.

Test preparation— Transfer 10.0mLof the solution under test to a suitable container.Proceed as directed for Standard preparation,beginning with “Add about 3.0g”.

Procedure— Proceed as directed in the Assay.

Tolerances— Not less than 85%(Q)of the labeled amount of C8H16O2is dissolved in 60minutes.

Internal standard solution— Dissolve a quantity of biphenyl in n-heptane to obtain a solution having a concentration of about 5mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Valproic Acid RSin n-heptane to obtain a solution having a known concentration of about 2.5mg per mL.Transfer 5.0mLto a container equipped with a closure.Add 2.0mLof Internal standard solution,close the container,and mix.

Assay preparation— Transfer not fewer than 20Capsules to a blender jar or other container,add about 150mLof methylene chloride,and cool in a solid carbon dioxide-acetone mixture until the contents have solidified.If necessary,transfer the mixture of Capsules and methylene chloride to a blender jar,and blend with a high-speed blender until all the solids are reduced to fine particles.Transfer the mixture to a 500-mLvolumetric flask,add n-heptane to volume,mix,and allow solids to settle.Transfer an accurately measured volume of this solution,equivalent to 250mg of valproic acid,to a 100-mLvolumetric flask,dilute with n-heptane to volume,and mix.Transfer 5.0mLto a container equipped with a closure.Add 2.0mLof Internal standard solution,close the container,and mix.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 2-mm ×1.8-m glass column packed with 10%phase G34on 80-to 100-mesh support S1A.The column temperature is maintained at about 150,and the injection port and the detector block temperatures are maintained at about 250.Dry helium is used as the carrier gas at a flow rate of about 40mLper minute.Chromatograph the Standard preparation,measure the peak responses,and calculate the ratio,RS,as directed for Procedure:the relative retention times are about 0.5for valproic acid and 1.0for biphenyl;the resolution,R,between valproic acid and biphenyl is not less than 3.0;the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 2µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses for valproic acid and biphenyl.Calculate the quantity,in mg,of valproic acid (C8H16O2)in the portion of Capsules taken by the formula: in which Cis the concentration,in mg per mL,of USP Valproic Acid RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.