Assay
Mobile phase
Dissolve 6.8g of monobasic potassium phosphate in water to make 1000mL,and adjust with 1
Mphosphoric acid to a pHof 3.0±0.1.Prepare a suitable mixture of this solution and methanol (4:1).Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Standard preparation
Quantitatively dissolve an accurately weighed quantity of
USP Aztreonam RSin
Mobile phaseto obtain a solution having a known concentration of about 1mg per mL.
Assay preparation
Transfer about 25mg of Aztreonam,accurately weighed,to a 25-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.
Chromatographic system
(see
Chromatography á621ñ)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 1.5mLper minute.Chromatograph the
Resolution solution,and record the peak responses as directed for
Procedure:the relative retention times are about 0.6for aztreonam and 1.0for 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 1000theoretical 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 20µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage of C
13H
17N
5O
8S
2in the portion of Aztreonam taken by the formula:
2.5(CSPS/W)(rU/rS),
in which
CSis the concentration,in mg per mL,of
USP Aztreonam RSin the
Standard preparation;PSis the assigned purity,in µg per mg,of
USP Aztreonam RS;
Wis the weight,in mg,of Aztreonam taken to prepare the
Assay preparation;and
rUand
rSare the aztreonam peak responses obtained from the
Assay preparationand the
Standard preparation,respectively.