á331ñAMPHETAMINE ASSAY

USP Reference Standards á11ñ— USP Dextroamphetamine Sulfate RS.

Standard Preparation— Dissolve a suitable quantity of USP Dextroamphetamine Sulfate RS,accurately weighed,in 2Nsulfuric acid (saturated with chloroform),and dilute quantitatively with the same solvent to obtain a solution having a known concentration of about 0.5mg of dextroamphetamine sulfate per mL.

Assay Preparation— Prepare as directed in the individual monograph.

Preparation of Chromatographic Column (see Chromatography á621ñ)— Pack a pledget of fine glass wool in the base of a 25-×300-mm chromatographic tube.Place 2g of purified siliceous earth in a 100-mLbeaker,add 1mLof 0.1Nhydrochloric acid,and mix until a fluffy mixture is obtained.Transfer the mixture to the column,and tamp moderately to compress the material into a uniform mass.Transfer the Assay Preparationto the column,dry-rinse the beaker with 1g of purified siliceous earth,and transfer to the column.Tamp a pledget of fine glass wool into place at the top of the column.

Procedure— Wash the column with 100mLof chloroform previously saturated with water,and discard the washings.Place under the column,as a receiver,a 125-mLseparator containing 10.0mLof 2Nsulfuric acid previously saturated with chloroform.Pass through the column 35mLof ammoniacal chloroform,prepared by equilibrating 2mLof ammonium hydroxide and 100mLof chloroform,and complete the elution with 70mLof chloroform previously saturated with water.Remove the separator,shake vigorously for 1minute,allow the layers to separate,discard the chloroform layer,and use the 10.0-mLacid solution of the sulfate salt of the amphetamine as the Assay Solution.Concomitantly determine the absorbance of the solution from the Standard Preparationand that of the Assay Solutionin 1-cm cells at 280nm and at the wavelength of maximum absorbance at about 257nm,with a suitable spectrophotometer,using 2Nsulfuric acid previously saturated with chloroform as the blank.Record the absorbance of the solution from the Standard Preparationas ASand that of the Assay Solutionas AU,and calculate as directed in the individual monograph.