pH3.6buffer— Dissolve 0.900g of anhydrous dibasic sodium phosphate and 1.298g of citric acid monohydrate in water to make 1000mL.

pH7.0buffer— Dissolve 5.68g of anhydrous dibasic sodium phosphate and 3.63g of monobasic potassium phosphate in water to make 1000mL.

Mobile phase— Prepare a suitable mixture of pH3.6bufferand acetonitrile (9:1).Pass through a membrane filter having a 10-µm or finer porosity,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Transfer 750mg of salicylic acid to a 100-mLvolumetric flask,dissolve in 10mLof methanol,dilute with pH7.0bufferto volume,and mix.

Standard preparation— Transfer about 25mg of USP Cefazolin RS,accurately weighed,to a 25-mLvolumetric flask,dissolve in and dilute with pH7.0bufferto volume,and mix.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,add 5.0mLof Internal standard solution,dilute with pH7.0bufferto volume,and mix.

Assay preparation— Proceed as directed for Standard preparation,except to use about 25mg of Cefazolin,accurately weighed.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.0-mm ×30-cm column that contains 10-µm packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.7for salicylic acid and 1.0for cefazolin;the resolution,R,between the analyte and internal standard peaks is not less than 4.0;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 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C14H14N8O4S3in the portion of Cefazolin taken by the formula: in which Cis the concentration,in mg per mL,of USP Cefazolin RS,calculated on the anhydrous basis,in the Standard preparation;and RUand RSare the peak response ratios of cefazolin to the internal standard obtained from the Assay preparationand the Standard preparation,respectively.