A: To 50mLof Oral Solution add 50mLof water and 50mLof 1Nsodium hydroxide,and stir.Cool the mixture at 4to 5for 30minutes:a white precipitate or cloudiness is observed.Add 100mLof water to the cooled mixture,stir,and filter by means of vacuum through a 47-mm membrane filter of 1-µm pore size.Wash the crystals with about 100mLof water,and allow to air-dry:the IRabsorption spectrum of a potassium bromide dispersion of the crystals so obtained exhibits maxima only at the same wavelengths as that of the crystalline base obtained from about 20mg of USP Trihexyphenidyl Hydrochloride RS,similarly prepared and measured.

B: The retention time exhibited by trihexyphenidyl hydrochloride in the chromatogram of the Assay preparationcorresponds to that of the Standard preparation,both relative to the internal standard,as obtained in the Assay.

Mobile phase andChromatographic system— Prepare as directed in the Assayunder Trihexyphenidyl Hydrochloride.

Standard preparation— Dissolve an accurately weighed quantity of USP Trihexyphenidyl Hydrochloride RSin methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having a known concentration of about 0.08mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 2mg of trihexyphenidyl hydrochloride,to a 25-mLvolumetric flask,dilute with methanol to volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Trihexyphenidyl Hydrochloride.Calculate the quantity,in mg,of trihexyphenidyl hydrochloride (C20H31NO·HCl)in each mLof the Oral Solution taken by the formula: in which Vis the volume,in mL,of Oral Solution taken to prepare the Assay preparation,and the other terms are as defined therein.