Assay
Mobile phase
Dissolve 6.8 g of monobasic potassium phosphate in water to make 1000 mL, and adjust with 1
M phosphoric acid to a pH of 3.0 ± 0.1. Prepare a suitable mixture of this solution and methanol (4:1). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation
Quantitatively dissolve an accurately weighed quantity of
USP Aztreonam RS in
Mobile phase to obtain a solution having a known concentration of about 1 mg per mL.
Assay preparation
Transfer about 25 mg of Aztreonam, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)The liquid chromatograph is equipped with a 270-nm detector, a 2-mm × 10-cm precolumn containing packing L2, and a 4.6-mm × 30-cm analytical column containing packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Resolution solution, and record the peak responses as directed for
Procedure: the relative retention times are about 0.6 for aztreonam and 1.0 for aztreonam E-isomer; the resolution,
R, between aztreonam and aztreonam E-isomer is not less than 2.0; the column efficiency as determined from the aztreonam peak is not less than 1000 theoretical plates; the tailing factor for the aztreonam peak is not more than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure
Separately inject equal volumes (about 20 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 percentage of C
13H
17N
5O
8S
2 in the portion of Aztreonam taken by the formula:
2.5(CSPS / W)(rU / rS),
in which
CS is the concentration, in mg per mL, of
USP Aztreonam RS in the
Standard preparation; PS is the assigned purity, in µg per mg, of
USP Aztreonam RS;
W is the weight, in mg, of Aztreonam taken to prepare the
Assay preparation; and
rU and
rS are the aztreonam peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.