Mobile phase,Standard preparation,Resolution solution,andChromatographic system— Proceed as directed in the Assay.

Test preparation— Use Assay preparation 1,prepared as directed in the Assay.

Procedure— Proceed as directed in the Assay.Calculate the percentage of arginine (C6H14N4O2)in the Aztreonam for Injection taken by the formula: in which CSis the concentration,in mg per mL,of USPL-Arginine RSin the Standard preparation;CUis the concentration,in mg per mL,of Aztreonam for Injection in Assay preparation 1,based on the weight,in mg,of Aztreonam for Injection removed from the container and the extent of dilution;and rUand rSare the arginine peak responses obtained from the Test preparationand the Standard preparation,respectively.Use this percentage to calculate,on the anhydrous and arginine-free basis,the assay result from Assay preparation 1,obtained as directed in the Assay.

Mobile phase— Dissolve 1.15g of monobasic ammonium phosphate in about 800mLof water.Adjust with phosphoric acid to a pHof 2.0±0.1,dilute with water to 1000mL,and mix.Prepare a suitable mixture of acetonitrile and this solution (750:250).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve accurately weighed quantities of USP Aztreonam RSand USPL-Arginine RSquantitatively in Mobile phaseto obtain a solution containing known concentrations of about 0.2mg of each per mL.

Resolution solution— Prepare a solution in Mobile phasecontaining in each mLabout 0.2mg each of USP Aztreonam RSand USP Open Ring Aztreonam RS.

Assay preparation 1— Weigh accurately 1container of Aztreonam for Injection.Transfer the contents of the container to a 100-mLvolumetric flask.Weigh the empty container,and calculate the weight,in mg,of Aztreonam for Injection removed.Dissolve the powder in the volumetric flask in Mobile phase,dilute with Mobile phaseto volume,and mix.Dilute an accurately measured volume of this solution quantitatively with Mobile phaseto obtain a solution having a concentration of about 0.2mg of aztreonam per mL.

Assay preparation 2— Constitute 1container of Aztreonam for Injection with a volume of water,accurately measured,corresponding to the volume of solvent specified in the labeling,except where the capacity of the container is 100mLor greater to constitute with 10mLof water.Withdraw the total withdrawable contents of the container,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution containing about 0.2mg of aztreonam per mL.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 206-nm detector,a 4.6-mm ×50-cm saturator precolumn containing packing L27,and a 4-mm ×25-cm analytical column containing packing L20.The flow rate is about 1mLper minute.Chromatograph the Resolution solution,and record the responses as directed for Procedure:the relative retention times are about 0.8for aztreonam and 1.0for open ring aztreonam;the column efficiency as determined from the aztreonam peak is not less than 1000theoretical plates,the resolution,R,between aztreonam and open ring aztreonam is not less than 2.0,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.The relative retention times are about 0.3for aztreonam and 1.0for arginine.Calculate the percentage of aztreonam (C13H17N5O8S2)in the Aztreonam for Injection taken by the formula: 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 the USP Aztreonam RS;CUis the concentration,in mg per mL,of Aztreonam for Injection in Assay preparation 1,based on the weight,in mg,of Aztreonam for Injection removed from the container and the extent of dilution;and rUand rSare the aztreonam peak responses obtained from Assay preparation 1and the Standard preparation,respectively.Calculate the quantity,in mg,of aztreonam (C13H17N5O8S2)in the container of Aztreonam for Injection used to prepare Assay preparation 2taken by the formula: 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,Lis the labeled quantity,in mg,of aztreonam in the container of Aztreonam for Injection;CUis the concentration,in mg per mL,of aztreonam in Assay preparation 2,on the basis of the labeled quantity,in mg,of aztreonam in the container and the extent of dilution;and rUand rSare the aztreonam peak responses obtained from Assay preparation 1and the Standard preparation,respectively.