A: The contents of the Capsules meet the requirements of Identificationtest Aunder Benzonatate.If a difference is observed,or if excipients are present,use an amount of the contents of Capsules equivalent to about 100mg of benzonatate,mixed with 25mLof 0.01Nhydrochloric acid,and proceed as directed under Identification—Organic Nitrogenous Bases á181ñ,beginning with “Transfer the liquid to a separator.”

B: The contents of the Capsules respond to Identificationtest Bunder Benzonatate.

Standard preparation— Transfer about 50mg of USP Benzonatate RS,accurately weighed,to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Assay preparation— Mix a number of Capsules,equivalent to about 500mg of benzonatate,with 40mLof chloroform in a suitable high-speed blender,and dilute with chloroform to 100.0mL.Transfer 10.0mLof this solution,equivalent to about 50mg of benzonatate,to a 100-mLvolumetric flask,and evaporate the chloroform on a steam bath with the aid of a current of air.Dissolve the residue in water,dilute with water to volume,and mix.

Procedure— Transfer 4.0mLeach of the Standard preparation,the Assay preparation,and water to provide the blank,to separate test tubes.To each tube add in succession 1.0mLof 1Mhydroxylamine hydrochloride and 1.0mLof 3.5Nsodium hydroxide,mixing after each addition.Allow to stand for 10minutes,accurately timed,then add 1.0mLof 3.5Nhydrochloric acid,mix,add 1.0mLof ferric chloride solution (8in 100),and mix.Allow to stand for 30minutes,accurately timed.Gently swirl the tubes for 1minute to remove any gas bubbles present,then concomitantly determine the absorbances of the solutions in 1-cm cells,at the wavelength of maximum absorbance at about 500nm,with a suitable spectrophotometer,using the blank to set the instrument.Calculate the quantity,in mg,of benzonatate (C30H53NO11av.)in the number of Capsules taken by the formula: in which Cis the concentration,in µg per mL,of USP Benzonatate RSin the Standard preparation;and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.