Limit of free salicylic acid— Mobile phase and Diluting solution—Prepare as directed in the Assay. Standard solution— Dissolve an accurately weighed quantity of USP Salicylic Acid RS in the Standard preparation prepared as directed in the Assay, to obtain a solution having a known concentration of about 0.015 mg of salicylic acid per mL. Test solution— Use the Stock solution prepared as directed for Assay preparation in the Assay. Chromatographic system— Use the Chromatographic system described in the Assay. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.7 for salicylic acid and 1.0 for aspirin; the resolution, R, between salicylic acid and aspirin is not less than 2.0; and the relative standard deviation of the salicylic acid peak responses is not more than 4.0%. Procedure— Proceed as directed for Procedure in the Assay. Calculate the percentage of salicylic acid (C7H6O3) in the portion of Tablets taken by the formula: 2000(C / QA)(rU / rS) in which C is the concentration, in mg per mL, of USP Salicylic Acid RS in the Standard solution; QA is the quantity, in mg, of aspirin (C9H8O4) in the portion of Tablets taken, as determined in the Assay, and rU and rS are the peak responses of the salicylic acid peaks obtained from the Test solution and the Standard solution, respectively: not more than 0.3% is found. In the case of Tablets that are coated, not more than 3.0% is found.
Limit of free salicylic acid— Dissolve 2.5 g in sufficient alcohol to make 25.0 mL. To each of two matched color-comparison tubes add 48 mL of water and 1 mL of a freshly prepared, diluted ferric ammonium sulfate solution (prepared by adding 1 mL of 1 N hydrochloric acid to 2 mL of ferric ammonium sulfate TS and diluting with water to 100 mL). Into one tube pipet 1 mL of a standard solution of salicylic acid in water, containing 0.10 mg of salicylic acid per mL. Into the second tube pipet 1 mL of the 1 in 10 solution of Aspirin. Mix the contents of each tube: after 30 seconds, the color in the second tube is not more intense than that in the tube containing the salicylic acid (0.1%).
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