Test solution— To a portion of powdered Tablets add 0.1Nhydrochloric acid to obtain a solution containing 4mg per mL.Use within 10minutes after preparation.

Application volume: 5µL.

Developing solvent system: a mixture of methanol,chloroform,water,and pyridine (90:80:30:10).

Procedure— Proceed as directed in the chapter.Dry the plate with the aid of a current of warm air for 10minutes.Locate the spots on the plate by spraying lightly with a solution of ninhydrin in alcohol containing 3mg per mL,and dry at 110for 15minutes.

Medium: water;900mL.

Apparatus 2: 75rpm.

Time: 90minutes.

pH5.0buffer— Dissolve 27.2g of monobasic potassium phosphate in 3liters of water,adjust with a 45%(w/w)solution of potassium hydroxide to a pHof 5.0±0.1,dilute with water to obtain 4liters of solution,and mix.

Mobile phase— Prepare a mixture of pH5.0bufferand acetonitrile (3900:100),and pass through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve an accurately weighed quantity of USP Amoxicillin RSin pH5.0bufferto obtain a solution having a known concentration of about 0.05mg per mL.Use this solution within 6hours.

Test solution— Pass a portion of the solution under test through a filter having a 0.5-µm or finer porosity.Quantitatively dilute an accurately measured volume of the filtrate with water to obtain a solution having an estimated concentration of about 0.045mg of amoxicillin (C16H19N3O5S)per mL.Use this solution within 6hours.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 230-nm detector,a 3.9-mm ×30-cm analytical column that contains packing L1and is maintained at a constant temperature of about 40±1,and a 2-mm ×2-cm guard column that contains packing L2.The flow rate is about 0.7mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the capacity factor,k¢,is between 1.1and 2.8;the column efficiency is not less than 1700theoretical plates;the tailing factor is not more than 2.5;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of amoxicillin (C16H19N3O5S)dissolved by the formula: in which Dis the dilution factor used in preparing the Test solution;Cis the concentration,in mg per mL,of USP Amoxicillin RSin the Standard solution;Pis the stated content,in µg of amoxicillin (C16H19N3O5S)per mg,of USP Amoxicillin RS;and rUand rSare the amoxicillin peak responses obtained from the Test solutionand the Standard solution,respectively.

Tolerances— Not less than 80%(Q)of the labeled amount of C16H19N3O5Sis dissolved in 90minutes.

FOR PRODUCTS LABELED AS CHEWABLE TABLETS— Proceed as directed above.

Tolerances— Not less than 70%(Q)of the labeled amount of C16H19N3O5Sis dissolved in 90minutes.

Diluent,Mobile phase,Standard preparation,and Chromatographic system— Prepare as directed in the Assayunder Amoxicillin.

Assay preparation— Place not fewer than 5Tablets in a high-speed glass blender jar containing an accurately measured volume of Diluentsufficient to yield a concentration of about 1mg of anhydrous amoxicillin per mL,blend for 4±1minutes,allow to stand for about 5minutes,and centrifuge a portion of the mixture.[NOTE—Where the volume of Diluent required would exceed 500mL,place 5Tablets in a volumetric flask of such capacity that when finally diluted to volume a concentration of about 1mg of anhydrous amoxicillin per mLwould be obtained.Add a volume of Diluent equivalent to about three-fourths of the capacity of the volumetric flask,and sonicate for about 5minutes.Dilute with Diluent to volume,add a magnetic stirring bar,and stir for about 30minutes.Centrifuge a portion of this solution.]Pass a portion of the clear supernatant through a suitable filter having a 1-µm or finer porosity,and use the filtrate as the Assay preparation.Use this solution within 6hours.

Procedure— Proceed as directed for Procedurein the Assayunder Amoxicillin.Calculate the quantity,in mg,of amoxicillin (C16H19N3O5S)in each Tablet taken by the formula: in which Vis the volume,in mL,of Diluentused to prepare the Assay preparation;and the other terms are as defined therein.