Assay
Diluent
Dissolve 13.6 g of monobasic potassium phosphate in 2000 mL of water, and adjust with a 45% (w/w) solution of potassium hydroxide to a pH of 5.0 ± 0.1.
Mobile phase
Prepare a suitable filtered mixture of
Diluent and acetonitrile (96:4). Make adjustments if necessary (see
System Suitability under
Chromatography
621![](/usp31/uspnf/pub/images/chars/rang.gif)
). Decrease the acetonitrile concentration to increase the retention time of amoxicillin.
Standard preparation
Quantitatively dissolve an accurately weighed quantity of
USP Amoxicillin RS in
Diluent to obtain a solution having a known concentration of about 1.2 mg per mL. Use this solution within 6 hours.
Assay preparation
Transfer about 240 mg of Amoxicillin, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. Use this solution within 6 hours.
Chromatographic system
(see
Chromatography
621![](/usp31/uspnf/pub/images/chars/rang.gif)
)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 1.5 mL per minute. Chromatograph the
Standard preparation, 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 2.0%.
Procedure
Separately inject equal volumes (about 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in µg, of C
16H
19N
3O
5S per mg of the Amoxicillin taken by the formula:
200(CP / W)(rU / rS)
in which
C is the concentration, in mg per mL, of
USP Amoxicillin RS in the
Standard preparation; P is the stated amoxicillin content, in µg per mg, of
USP Amoxicillin RS;
W is the quantity, in mg, of Amoxicillin taken to prepare the
Assay preparation; and
rU and
rS are the amoxicillin peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.