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

Application volume: 5 µL.

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 10 minutes. Locate the spots on the plate by spraying lightly with a solution of ninhydrin in alcohol containing 3 mg per mL, and dry at 110 for 15 minutes.

Medium: water; 900 mL.

Apparatus 2: 75 rpm.

Time: 30 minutes.

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

Mobile phase— Prepare a mixture of pH 5.0 Buffer and acetonitrile (3900:100), and pass through a filter having a 0.5-µm or finer porosity. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of USP Amoxicillin RS in pH 5.0 Buffer to obtain a solution having a known concentration of about 0.05 mg per mL. Use this solution within 6 hours.

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 0.045 mg of amoxicillin per mL. Use this solution within 6 hours.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector, a 3.9-mm × 30-cm analytical column that contains packing L1, and a 2-mm × 2-cm guard column that contains packing L2. The analytical column is maintained at a constant temperature of about 40 ± 1. The flow rate is about 0.7 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the capacity factor, k¢, is between 1.1 and 2.8; the column efficiency is not less than 1700 theoretical 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 10 µL) of the Standard solution and the Test solution into 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 D is the dilution factor used in preparing the Test solution; C is the concentration, in mg per mL, of USP Amoxicillin RS in the Standard solution; P is the stated content, in µg of amoxicillin (C16H19N3O5S) per mg, of USP Amoxicillin RS; and rU and rS are the amoxicillin peak responses obtained from the Test solution and the Standard solution, respectively.

Tolerances— Not less than 75% (Q) of the labeled amount of C16H19N3O5S is dissolved in 30 minutes.

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

FOR VETERINARY PRODUCTS— Proceed as directed above, except to use Apparatus 2 at 100 rpm.

(Official January 1, 2007)

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

Assay preparation— Place not fewer than 5 Tablets in a high-speed glass blender jar containing an accurately measured volume of Diluent sufficient to yield a concentration of about 1 mg of anhydrous amoxicillin per mL, blend for 4 ± 1 minutes, allow to stand for about 5 minutes, and centrifuge a portion of the mixture. [NOTE—Where the volume of Diluent required would exceed 500 mL, place 5 Tablets in a volumetric flask of such capacity that when finally diluted to volume a concentration of about 1 mg of anhydrous amoxicillin per mL would be obtained. Add a volume of Diluent equivalent to about three-fourths of the capacity of the volumetric flask, and sonicate for about 5 minutes. Dilute with Diluent to volume, add a magnetic stirring bar, and stir for about 30 minutes. 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 6 hours.

Procedure— Proceed as directed for Procedure in the Assay under Amoxicillin. Calculate the quantity, in mg, of amoxicillin (C16H19 N3O5S) in each Tablet taken by the formula: in which V is the volume, in mL, of Diluent used to prepare the Assay preparation; and the other terms are as defined therein.