Change to read:

Solution A— Transfer about 26.2mLof acetic acid and about 99.12g of potassium acetate to a 4-Lvolumetric flask.Add 2000mLof water,and mix to dissolve.Dilute with water to volume,and pass through a 0.45-µm nylon filter.

Solution B— Use acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments,if necessary (see System Suitabilityunder Chromatography á621ñ).

Extraction solution: a mixture of 400mLof acetic acid and 600mLof water.

Dilution buffer— Dissolve about 205g of potassium acetate in about 800mLof water.Adjust with acetic acid to a pHof 7.5to 8.2.Dilute with water to 1000mL,and pass through a 0.45-µm nylon filter.

10%Acetic acid solution— Add about 10.0mLof acetic acid to a 100-mLvolumetric flask.Mix,and dilute with water to volume.

System suitability solution— Dissolve an accurately weighed quantity of USP Cephapirin Sodium RSin 10%Acetic acid solutionto prepare a solution containing a known concentration of about 2.0mg per mL.Heat the solution at 50for 12to 18hours.

Standard preparation— In duplicate,accurately weigh about 50mg of USP Cephapirin Sodium RS,and transfer into a 25-mLvolumetric flask.Add about 2.5mLof Extraction solutionand about 15.0mLof Dilution buffer,and agitate to dissolve.Add 7.0mLof acetonitrile,and mix well.Allow the solution to return to room temperature,and dilute with water to volume.

Assay preparation— In duplicate,weigh about 60mg of Cephapirin Benzathine,and transfer into a 25-mLvolumetric flask.Add about 2.5mLof Extraction solutionand 15.0mLof Dilution buffer,and mix to dissolve.Add 7.0mLof acetonitrile,and mix.Allow the flask to return to room temperature,and dilute with water to volume.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 260-nm detector,a 3.2-mm ×15-mm guard column that contains 7-µm packing L1and a 3.9-mm ×15-cm analytical column that contains 4-µm packing L1.The flow rate is about 2.0mLper minute,and the columns are heated to 40.The chromatograph is programmed as follows. Chromatograph the System suitability solutionand the Standard preparation,and record the peak heights and valleys as directed forProcedure.Using the results from the System suitability solution,calculate the percentage of the height of the valley taken by the formula: in which rVis the height of the valley between cephapirin and any impurity;and riis the impurity peak height.The percentage of the height of the valley is not more than 25%for the impurity peaks adjacent to the cephapirin peak.[note—The System suitability solutionis acceptable as long as the cephapirin peak is larger than the two peaks on either side of the cephapirin peak.]The relative standard deviation for replicate injections of the Standard preparationis not more than 3.0%.

Procedure— Separately inject equal volumes (about 2µL)of the duplicate Standard preparationand the duplicate Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in µg,of C17H17N3O6S2in each mg of Cephapirin Benzathine taken by the formula: in which Pis the assigned potency,in µg of cephapirin per mg,of USP Cephapirin Sodium RS;WSand WUare the quantities of USP Cephapirin Sodium RSand Cephapirin Benzathine,in mg,used to prepare the Standard preparationand the Assay preparation,respectively;VSand VUare the final volumes,in mL,of the Standard preparationand the Assay preparation,respectively;and rUand rSare the average peak areas of the cephapirin peaks obtained from the Assay preparationand the Standard preparation,respectively.USP28