Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 1: 100rpm.

Time: 120minutes.

Mobile phase— Prepare a filtered and degassed mixture of water,isopropanol,acetonitrile,and glacial acetic acid (22:11:7:0.4).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve an accurately weighed quantity of USP Sulfasalazine RSin 0.1Nsodium hydroxide,and dilute quantitatively,and stepwise if necessary,with 0.1Nsodium hydroxide to obtain a solution having a known concentration of about 55.6µg per mL.

Test solution— Pass about 7mLof the solution under test through a membrane filter having a 0.45-µm porosity.

Chromatographic system (seeChromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the retention time for sulfasalazine is about 7.7minutes;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Inject a volume (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,and measure the peak responses.Calculate the percentage of C18H14N4O5Sdissolved by the formula: in which CSis the concentration,in mg per mL,of USP Sulfasalazine RSin the Standard solution;LCis the label claim,in mg;and rUand rSare the peak responses obtained from the Test solutionand the Standard solution,respectively.

Tolerances— Not more than 10%of the labeled amount of C18H14N4O5Sis dissolved in 120minutes.

Medium: pH7.5phosphate buffer;900mL.

Apparatus 1: 100rpm.

Time: 60minutes.

Tolerances— Not less than 85%(Q)of the labeled amount of C18H14N4O5Sis dissolved in 60minutes.