331 AMPHETAMINE ASSAY

USP Reference Standards 11— USP Dextroamphetamine Sulfate RS.

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

Assay Preparation— Prepare as directed in the individual monograph.

Preparation of Chromatographic Column (see Chromatography 621)—Pack a pledget of fine glass wool in the base of a 25- × 300-mm chromatographic tube. Place 2 g of purified siliceous earth in a 100-mL beaker, add 1 mL of 0.1 N hydrochloric 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 Preparation to the column, dry-rinse the beaker with 1 g 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 100 mL of chloroform previously saturated with water, and discard the washings. Place under the column, as a receiver, a 125-mL separator containing 10.0 mL of 2 N sulfuric acid previously saturated with chloroform. Pass through the column 35 mL of ammoniacal chloroform, prepared by equilibrating 2 mL of ammonium hydroxide and 100 mL of chloroform, and complete the elution with 70 mL of chloroform previously saturated with water. Remove the separator, shake vigorously for 1 minute, allow the layers to separate, discard the chloroform layer, and use the 10.0-mL acid solution of the sulfate salt of the amphetamine as the Assay Solution. Concomitantly determine the absorbance of the solution from the Standard Preparation and that of the Assay Solution in 1-cm cells at 280 nm and at the wavelength of maximum absorbance at about 257 nm, with a suitable spectrophotometer, using 2 N sulfuric acid previously saturated with chloroform as the blank. Record the absorbance of the solution from the Standard Preparation as AS and that of the Assay Solution as AU, and calculate as directed in the individual monograph.

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