Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 120 minutes.

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 Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— 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 1 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the retention time for sulfasalazine is about 7.7 minutes; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Inject a volume (about 10 µL) of the Standard solution and the Test solution into the chromatograph, and measure the peak responses. Calculate the percentage of C18H14N4O5S dissolved by the formula: in which CS is the concentration, in mg per mL, of USP Sulfasalazine RS in the Standard solution; LC is the label claim, in mg; and rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively.

Tolerances— Not more than 10% of the labeled amount of C18H14N4O5S is dissolved in 120 minutes.

Medium: pH 7.5 phosphate buffer; 900 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

Tolerances— Not less than 85% (Q) of the labeled amount of C18H14N4O5S is dissolved in 60 minutes.

Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 120 minutes.

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 Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— 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 1 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the retention time for sulfasalazine is about 7.7 minutes; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Inject a volume (about 10 µL) of the Standard solution and the Test solution into the chromatograph, and measure the peak responses. Calculate the percentage of C18H14N4O5S dissolved by the formula: in which CS is the concentration, in mg per mL, of USP Sulfasalazine RS in the Standard solution; LC is the label claim, in mg; and rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively.

Tolerances— Not more than 10% of the labeled amount of C18H14N4O5S is dissolved in 120 minutes.

Medium: pH 7.5 phosphate buffer; 900 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

Tolerances— Not less than 85% (Q) of the labeled amount of C18H14N4O5S is dissolved in 60 minutes.