A: Prepare a test solution containing the equivalent of 4mg of mezlocillin per mL.Prepare a Standard solution of USP Mezlocillin Sodium RScontaining 4mg per mL.Use within 10minutes after preparation.Apply separately 5µLof each solution to a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel mixture (see Chromatography á621ñ).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 10minutes.Locate the spots on the plate by exposing it to iodine vapors in a closed chamber for about 30seconds:the RFvalue 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 á191ñ.

Test solution: 10mg per mL,in water.

Mobile phase— Dissolve 4.9g of monobasic potassium phosphate and 0.54g of dibasic potassium phosphate in about 500mLof water,dilute with water to 1000mL,and mix.Prepare a suitable mixture of this solution and acetonitrile (855:145),and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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 500µg of mezlocillin (C21H25N5O8S2)per mL.

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

Chromatographic system (see Chromatography á621ñ)—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 2mLper minute.Chromatograph the Standard preparation,and record the responses as directed under Procedure:the column efficiency is not less than 1500theoretical 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 20µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in µg per mL,of mezlocillin (C21H25N5O8S2)in the Standard preparation,Wis the weight,in mg,of the portion of Mezlocillin Sodium taken to prepare the Assay preparation,and rUand rSare the mezlocillin peak responses obtained from the Assay preparationand the Standard preparation,respectively.