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 volume of Oral Solution,equivalent to about 250mg of valproic acid,in a separator.Add 40mLof water and 2mLof 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.

Internal standard solution,Standard preparation,and Chromatographic system— Prepare as directed in the Assayunder Valproic Acid Capsules.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 250mg of valproic acid,to a separator.Add 40mLof water and 2mLof hydrochloric acid,mix,and extract gently with 80mLof n-heptane until the aqueous layer is clear (about 3minutes).Filter the n-heptane layer through glass wool,collecting the filtrate in a 100-mLvolumetric flask.Rinse the separator and the glass wool with small portions of n-heptane,add the rinsings to the 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.

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 each mLof the Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Valproic Acid RSin the Standard preparation;Vis the volume,in mL,of Oral Solution taken;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.