A: Ultraviolet Absorption 197U—

B: Transfer a volume of Injection equivalent to about 50 mg of xylazine to a separator, add 1 mL of sodium carbonate solution (1 in 20), and extract with four 10-mL portions of methylene chloride, combining the methylene chloride extracts in a beaker and evaporating to dryness. Add 10 mL of methanol to the beaker, and swirl to dissolve the residue. The test solution thus obtained responds to Identification test B under Xylazine Hydrochloride.

Mobile phase— Dissolve 6.0 g of sodium 1-heptanesulfonate in 3000 mL of water, adjust to a pH of 3.0 by dropwise addition of phosphoric acid. Add 1000 mL of acetonitrile, mix, and pass through a filter having a 0.5-µm or finer porosity. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed portion of USP Xylazine Hydrochloride RS quantitatively in Mobile phase to obtain a solution having a known concentration of about 1.2 mg per mL. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass a portion of this solution through a filter having a 0.5-µm or finer porosity, discarding the first 3 mL of the filtrate. Use the clear filtrate as the Standard preparation. This solution contains about 0.12 mg of USP Xylazine Hydrochloride RS per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 200 mg of xylazine, to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of this solution to a second 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass a portion of this solution through a filter having a 0.5-µm or finer porosity, discarding the first 3 mL of the filtrate. Use the clear filtrate as the Assay preparation.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector, a 2-mm × 2-cm guard column that contains packing L2, and a 4.6-mm × 25-cm analytical column that contains packing L1 and is maintained at a constant temperature of about 40. The flow rate is about 1 mL per minute. Chromatograph the Assay preparation, and record the peak responses as directed for Procedure: the resolution, R, between the main xylazine peak and the closest eluting other peak, if any, is not less than 2.5; and the tailing factor for the xylazine peak is not more than 2.0. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%. [note—After daily use, rinse the column with 100 mL of water and with 100 mL of methanol, and store the column containing methanol.]

Procedure— Separately inject equal volumes (about 20 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 xylazine (C12H16N2S) in each mL of the Injection taken by the formula: in which 220.34 and 256.80 are the molecular weights of xylazine and xylazine hydrochloride, respectively; C is the concentration, in mg per mL, of USP Xylazine Hydrochloride RS in the Standard preparation; V is the volume, in mL, of Injection taken to prepare the Assay preparation; and rU and rS are the areas of the xylazine peak responses in the chromatograms obtained from the Assay preparation and the Standard preparation, respectively.