A: Prepare a test solution containing the equivalent of 4 mg of mezlocillin per mL. Prepare a Standard solution of USP Mezlocillin Sodium RS containing 4 mg per mL. Use within 10 minutes after preparation. Apply separately 5 µL of each solution to a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture (see Chromatography 621). Place the plate in a suitable chromatographic chamber, and develop the chromatogram with a solvent system consisting of a mixture of methanol, chloroform, water, and pyridine (90:80:30:10) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the chamber, and dry with a current of warm air for 10 minutes. Locate the spots on the plate by exposing it to iodine vapors in a closed chamber for about 30 seconds: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

B: It responds to the tests for Sodium 191.

Test solution: 10 mg per mL, in water.

Mobile phase— Dissolve 4.9 g of monobasic potassium phosphate and 0.54 g of dibasic potassium phosphate in about 500 mL of water, dilute with water to 1000 mL, and mix. Prepare a suitable mixture of this solution and acetonitrile (855:145), and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve a suitable quantity of USP Mezlocillin Sodium RS, accurately weighed, in water to obtain a solution having a known concentration of about 500 µg of mezlocillin (C21H25N5O8S2) per mL.

Assay preparation— Transfer about 110 mg of Mezlocillin Sodium, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 210-nm detector and a 4-mm × 12.5-cm column containing 5-µm packing L1, and is maintained at 40 ± 1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the responses as directed under Procedure: the column efficiency is not less than 1500 theoretical plates, the tailing factor is not more than 1.5, and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— [note—Use peak areas where peak responses are indicated.] 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 µg per mg, of mezlocillin (C21H25N5O8S2) in each mg of the Mezlocillin Sodium taken by the formula: in which C is the concentration, in µg per mL, of mezlocillin (C21H25N5O8S2) in the Standard preparation, W is the weight, in mg, of the portion of Mezlocillin Sodium taken to prepare the Assay preparation, and rU and rS are the mezlocillin peak responses obtained from the Assay preparation and the Standard preparation, respectively.