A: Dissolve about 100 mg in 5 mL of water, add 5 mL of 1 N sodium hydroxide, cool to about 10, add 1 mL of a mixture of absolute ether and benzoyl chloride (2:1), insert the stopper, and shake for 3 minutes. Filter the precipitate, wash with about 10 mL of cold water, and recrystallize from diluted alcohol: the crystals of the benzoyl derivative of amphetamine so obtained, after drying at 80 for 3 hours, melt between 131 and 135, the procedure for Class I being used (see Melting Range or Temperature 741).

B: A solution (1 in 10) responds to the tests for Sulfate 191.

Diluent— Dilute 3.12 mL of phosphoric acid with water to 1000 mL.

Buffer solution— Dissolve 2.16 g of sodium 1-octanesulfonate in 1000 mL of water, and add 1.0 mL of triethylamine. Mix, and adjust with phosphoric acid to a pH of 2.5.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solution, acetonitrile, and methanol (144:37:19). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard stock solution— Dissolve an accurately weighed quantity of USP Dextroamphetamine Sulfate RS in Diluent to obtain a solution having a known concentration of about 0.3 mg per mL.

Standard solution— Dilute an accurately measured volume of Standard stock solution in Diluent to obtain a solution having a known concentration of about 0.003 mg per mL.

Test solution— Transfer about 30 mg of Amphetamine Sulfate, accurately weighed, to a 100-mL volumetric flask. Dissolve in 50 mL of Diluent, sonicate for 5 minutes, dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 215-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard stock solution, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%. Chromatograph the Test solution, and record the peak responses as directed for Procedure: the resolution, R, between amphetamine and any adjacent peak, if any, is not less than 1.5.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of each impurity in the portion of Amphetamine Sulfate taken by the formula: in which C is the concentration, in mg per mL, of USP Dextroamphetamine Sulfate RS in the Standard solution; W is the weight, in mg, of Amphetamine Sulfate taken to prepare the Test solution; ri is the peak response for each impurity obtained from the Test solution; and rS is the peak response for amphetamine obtained from the Standard solution: not more than 0.1% of any individual impurity is found, and not more than 0.5% of total impurities is found.