Mobile phase— Prepare a filtered and degassed mixture of 0.01 M tetrabutylammonium hydrogen sulfate and acetonitrile (86:14). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of USP Alfentanil Hydrochloride RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.54 mg per mL.

Test solution— Transfer about 54 mg of Alfentanil Hydrochloride, accurately weighed, to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 235-nm detector and a 4.6-mm × 25-cm column that contains spherical 5-µm packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed under Procedure: the column efficiency is not less than 5400 theoretical plates, the tailing factor is not more than 1.3, and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Inject a volume (about 25 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the responses for all of the peaks. Calculate the percentage of each impurity in the portion of Alfentanil Hydrochloride taken by the formula: in which ri is the response of each impurity peak, and rs is the sum of all of the peaks: not more than 0.5% of any single impurity is found, and the sum of all impurities is not more than 1.0%.