Alkaline borate solution— Dissolve 6.2g of boric acid and 7.45g of potassium chloride in 500mLof water,add 210mLof sodium hydroxide solution (1in 25),and mix.Add water to make 2000mLof solution,and mix.

Standard solution— [NOTE—Prepare the Standard solution and the Test solution concomitantly.]Dissolve an accurately weighed quantity of USP Mephobarbital RSin Alkaline borate solutionto obtain a solution having a concentration of about 10mg per mL,and quantitatively dilute with water to obtain a solution having a known concentration of about 1.5mg per mL.

Test solution— Transfer 1Tablet to a glass-stoppered centrifuge tube,crush the tablet,and add 25.0mLof Alkaline borate solution.Insert the stopper,shake for 10minutes,and centrifuge until clear,filtering the supernatant,if necessary.Dilute a portion of the subsequent liquid quantitatively,and stepwise if necessary,with water to obtain a solution having a concentration of about 1.5mg of mephobarbital per mL.

Procedure— Transfer 3.0mLeach of the Standard solutionand the Test solutionto separate 200-mLvolumetric flasks,dilute each with a 1in 3solution of Alkaline borate solutionin water to volume,and mix.Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 245nm,with a suitable spectrophotometer,using a 1in 3solution of Alkaline borate solutionin water as the blank.Calculate the quantity,in mg,of C13H14N2O3in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of mephobarbital in the Tablet;Cis the concentration,in mg per mL,of USP Mephobarbital RSin the Standard solution;Dis the concentration,in mg per mL,of mephobarbital in the Test solution,based upon the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solutions from the Test solutionand the Standard solution,respectively.