Assay
Pipet a volume of Injection,equivalent to about 500mg of pentobarbital sodium,into a separator,and dilute with water to about 15mL.To the solution add 2mLof hydrochloric acid,shake,and completely extract the liberated pentobarbital with 25-mLportions of chloroform.Test for completeness of extraction by extracting with an additional 10-mLportion of chloroform and evaporating the solvent:not more than 0.5mg of residue remains.Filter each extract through a pledget of chloroform-washed cotton,or other suitable filter,into a tared beaker,and finally wash the separator and the filter with several small portions of chloroform.Evaporate the combined filtrate and washings on a steam bath with the aid of a current of air,add 10mLof ether,again evaporate,dry the residue at 105

for 2hours,cool,and weigh.The weight of the residue,multiplied by 1.097,represents the weight of pentobarbital sodium (C
11H
17N
2NaO
3).