A:Infrared Absorption á197Kñ.

B: Place a suitable thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of binder-free silica gel in a chamber containing a mixture of n-hexane and tetradecane (95:5)to a depth of about 1cm,allow the solvent front to move the length of the plate,remove the plate from the chamber,and allow the solvent to evaporate.Apply 20µLeach of a solution of Cefadroxil in water containing 2mg per mLand a similarly prepared Standard solution of USP Cefadroxil RSto this plate.Allow the spots to dry,and develop the chromatogram in a solvent system consisting of 0.1Mcitric acid,0.1Mdibasic sodium phosphate,and a 1in 15solution of ninhydrin in acetone (60:40:1.5)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,mark the solvent front,and allow to air-dry.Spray the plate with a 1in 500solution of ninhydrin in dehydrated alcohol [NOTE—Protect this solution from light],dry for 10minutes at 110,and examine the chromatogram:the RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Test solution: 10mg per mL,in water.

Adsorbent: a 0.25-mm layer of chromatographic silica gel mixture.

Solvent— Prepare a mixture of alcohol,water,and 2.4Nhydrochloric acid (75:22:3).

Test solution— Prepare a solution of Cefadroxil in Solventcontaining 25mg per mL.

Standard solution 1— Dilute 1.0mLof the Test solutionwith Solvent to 100mL,and mix.

Standard solution 2— Prepare a solution in Solventcontaining 0.25mg each of 7-aminodesacetoxycephalosporanic acid and D-a-4-hydroxyphenylglycine per mL.

Standard solution 3— Prepare a solution in Solvent containing 0.25mg of D-a-4-hydroxyphenylglycine per mL.

Resolution solution— Mix 1.0mLof the Test solutionand 1.0mLof Standard solution 2.

Developing solvent system: a mixture of ethyl acetate,alcohol,water,and formic acid (14:5:5:1).

Procedure— Apply separate 2-µLportions of the Test solution,Standard solution 1,Standard solution 2,and Standard solution 3,and a 4-µLportion of the Resolution solutionto a suitable thin-layer chromatographic plate (see Thin-Layer Chromatographyunder Chromatography á621ñ),and develop the chromatograms until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,mark the solvent front,allow the plate to dry,and examine the chromatograms under short-wavelength UVlight:any secondary spot in the chromatogram obtained from the Test solutioncorresponding to 7-aminodesacetoxycephalosporanic acid or D-a-4-hydroxyphenylglycine is not more intense than the corresponding spot in the chromatogram obtained from Standard solution 2(1.0%);and any spot,other than the principal spot and any spot corresponding to 7-aminodesacetoxycephalosporanic acid or D-a-4-hydroxyphenylglycine,is not more intense than the principal spot in the chromatogram obtained from Standard solution 1(1.0%).In a valid test,the chromatogram obtained from the Resolution solutionshows three clearly separated spots.

pH5.0Buffer— Dissolve 13.6g of monobasic potassium phosphate in water to make 2000mLof solution.Adjust with 10Npotassium hydroxide to a pHof 5.0,and mix.

Mobile phase— Prepare a suitable mixture of pH5.0Bufferand acetonitrile (960:40),and pass through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Increasing the acetonitrile content of the Mobile phasedecreases the retention time of cefadroxil,and decreasing the acetonitrile content increases the retention time.

Standard preparation— Dissolve an accurately weighed quantity of USP Cefadroxil RSin pH5.0Bufferto obtain a solution having a known concentration of about 1.06mg per mL.This solution contains the equivalent of about 1000µg of cefadroxil (C16H17N3O5S)per mL.Use this solution on the day prepared.

Assay preparation— Transfer about 212mg of Cefadroxil,accurately weighed,to a 200-mLvolumetric flask,dilute with pH5.0Bufferto volume,and stir by mechanical means for 5minutes until dissolved.Use this solution on the day prepared.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 230-nm detector and a 4-mm ×25-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the capacity factor,k ¢,is between 2.0and 3.5;the column efficiency determined from the analyte peak is not less than 1800theoretical plates;the tailing factor for the analyte peak is not more than 2.2;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 areas for the major peaks.Calculate the quantity,in µg,of cefadroxil (C16H17N3O5S)in each mg of the Cefadroxil taken by the formula: in which Cis the concentration,in mg per mL,of USP Cefadroxil RStaken to prepare the Standard preparation;Eis the cefadroxil equivalent,in µg per mg,of USP Cefadroxil RS;Wis weight,in mg,of the portion of Cefadroxil taken;and rUand rSare the cefadroxil peak responses obtained from the Assay preparationand the Standard preparation,respectively.