Mobile phase— Prepare a mixture of water,methanol,and glacial acetic acid (68:30:2).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Extractant— Prepare a mixture of 0.15Nhydrochloric acid and methanol (3:1).

Standard preparation— Prepare a solution of USP Sulfamethazine RSin Extractanthaving a known concentration of about 0.01mg per mL.

Assay preparation— Transfer about 5g of Sulfamethazine Granulated,accurately weighed,to a suitable container,add 250.0mLof Extractant,and shake by mechanical means for 2hours.Allow the mixture to settle,storing the mixture in a refrigerator if settling is allowed to continue overnight.Filter a portion of the supernatant,and transfer 10.0mLof the clear filtrate to a 100-mLvolumetric flask.Dilute with Extractantto volume,and mix.Transfer 5.0mLof this solution to a 200-mLvolumetric flask,dilute with Extractantto volume,and mix.Filter a portion of this solution through a filter having a porosity of 0.5µm or finer,and use the filtrate as the Assay preparation.This solution contains about 0.01mg of sulfamethazine per mL.

Derivatizing reagent— Dissolve 6.0g of dimethylaminobenzaldehyde in 200mLof glacial acetic acid,add 120mLof methanol and 80mLof water,mix,and degas.Prepare this reagent daily.

Chromatographic system— The liquid chromatograph is equipped with a guard column that contains packing L1,a 4.6-mm ×25-cm analytical column that contains packing L1,a separate pump to deliver the Derivatizing reagentvia a T-junction installed immediately post-column,a post-column derivatization coil consisting of 3-m ×0.5-mm inside-diameter polytef tubing,a flow cell,and a 450-nm detector.The Mobile phaseflow rate is about 2mLper minute,and the Derivatizing reagentflow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,for the sulfamethazine peak is not less than 2.0,and the relative standard deviation for replicate injections is not more than 3.5%.

Procedure— Separately inject equal volumes (about 100µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the sulfamethazine peaks.Calculate the quantity,in mg,of sulfamethazine (C12H14N4O2S)in each g of the Sulfamethazine Granulated taken by the formula: in which Cis the concentration,in mg per mL,of USP Sulfamethazine RSin the Standard preparation,Wis the quantity,in g,of Sulfamethazine Granulated taken to prepare the Assay preparation,and rUand rSare the sulfamethazine peak responses obtained from the Assay preparationand the Standard preparation,respectively.