A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

C: Dissolve about 500 mg in 5 mL of water, and render the mixture alkaline with 1 N sodium hydroxide. Extract with three 5-mL portions of methylene chloride: the aqueous layer meets the requirements of the tests for Citrate 191.

D: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Standard solution— Pipet 25 µL of acetone into a 100-mL volumetric flask, dilute with dimethylformamide to volume, and mix.

Test solution— Dissolve 100 mg of Sufentanil Citrate, accurately weighed, in 2.0 mL of dimethylformamide contained in a polytef-lined screw-cap vial.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 4-mm × 1.83-m glass column containing support S2. The carrier gas is nitrogen with a flow rate of about 50 mL per minute. The injection port temperature and the detector temperature are both maintained at 230. The column temperature is maintained at 175. Inject the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation of the acetone peak responses for replicate injections is not more than 5%.

Procedure— Separately inject equal volumes (about 2 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. [note—After injecting the Test solution, wait about 25 minutes to allow the sufentanil peak to completely elute from the column.] Calculate the percentage of acetone in the portion of Sufentanil Citrate taken by the formula: in which CS is the concentration, in mg per mL, of acetone in the Standard solution; CU is the concentration, in mg per mL, of sufentanil citrate in the Test solution; and rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively. Not more than 0.5% of acetone is found.

Mobile phase and Chromatographic system— Proceed as directed in the Assay.

Blank solution— Transfer 33.2 mg of citric acid, accurately weighed, to a 50-mL volumetric flask. Dilute with Mobile phase to volume, and mix.

Test solution— Transfer about 7.5 mg of Sufentanil Citrate to a 10-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Procedure— Separately inject equal volumes (about 100 µL) of the Blank solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses. Calculate the percentage of each impurity, disregarding any peaks corresponding to those found in the Blank solution, in the portion of Sufentanil Citrate taken by the formula: in which ri is the peak response for each impurity; and rs is the sum of the responses of all of the peaks: not more than 0.5% of any impurity is found, and the sum of all impurities is not more than 1.0%.

Mobile phase— Prepare a filtered and degassed mixture of methanol, 0.13 M ammonium acetate, and acetonitrile (45:31:24). Adjust with glacial acetic acid or ammonium hydroxide to a pH of 7.2. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Sufentanil Citrate RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.075 mg per mL.

Assay preparation— Transfer about 18.7 mg of Sufentanil Citrate, accurately weighed, to a 25-mL volumetric flask; dissolve in and dilute with Mobile phase to volume; and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 228-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C22H30N2O2S·C6H8O7 in the portion of Sufentanil Citrate taken by the formula: in which C is the concentration, in mg per mL, of USP Sufentanil Citrate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.