Salicylic Acid
(sal'' i sil' ik as' id).
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C7H6O3 138.12

Benzoic acid, 2-hydroxy-.
Salicylic acid [69-72-7].
» Salicylic Acid contains not less than 99.5 percent and not more than 101.0 percent of C7H6O3, calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers.
USP Reference standards 11
USP Phenol RS Click to View Structure
USP Salicylic Acid RS Click to View Structure
USP Salicylic Acid Related Compound A RS Click to View Structure
4-Hydroxybenzoic acid.
    C7H6O3    138.12[CAS-99-96-7].
USP Salicylic Acid Related Compound B RS Click to View Structure
4-Hydroxyisophthalic acid.
    C8H6O4    182.13
Identification— In moderately dilute solutions of Salicylic Acid, ferric chloride TS produces a violet color.
Melting range 741: between 158 and 161.
Loss on drying 731 Dry it over silica gel for 3 hours: it loses not more than 0.5% of its weight.
Residue on ignition 281: not more than 0.05%.
Chloride 221 Heat 1.5 g with 75 mL of water until the acid is dissolved, cool, add water to restore the original volume, and filter: a 25-mL portion of the filtrate shows no more chloride than corresponds to 0.10 mL of 0.020 N hydrochloric acid (0.014%).
Sulfate 221 A 1.0-g portion dissolved in a mixture of alcohol and water (1:1) shows no more sulfate than corresponds to 0.2 mL of 0.020 N sulfuric acid (0.02%).
Heavy metals— Dissolve 1 g in 25 mL of acetone, and add 2 mL of water. Add 1.2 mL of thioacetamide-glycerin base TS and 2 mL of pH 3.5 Acetate Buffer, and allow to stand for 5 minutes: any color produced is not darker than that of a control made with 25 mL of acetone and 2 mL of Standard Lead Solution (see Heavy Metals 231) and treated in the same manner. The limit is 20 µg per g.
Related compounds—
Mobile phase— Prepare a mixture of water, methanol, and glacial acetic acid (60:40:1). Make adjustments if necessary (see System Suitability under Chromatography 621).
Diluent— Prepare a mixture of methanol, water, and glacial acetic acid (70:30:4).
Standard solution— Dissolve accurately weighed quantities of USP Salicylic Acid Related Compound A RS, USP Salicylic Acid Related Compound B RS, USP Phenol RS, and USP Salicylic Acid RS in Diluent to obtain a solution having known concentrations of about 0.05 mg per mL, 0.025 mg per mL, 0.01 mg per mL, and 0.5 mg per mL, respectively.
Test solution— Prepare a solution of Salicylic Acid in Diluent containing 50 mg per mL. Sonicate until completely dissolved.
Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 270-nm detector and a 4.6-mm × 10-cm column containing 5-µm packing L1. The flow rate is about 0.5 mL per minute. Chromatograph the Standard solution, record the chromatograms, and identify the peaks using the relative retention times given in Table 1. [noteFor the purpose of peak identification the approximate relative retention times are given in Table 1. The relative retention times are measured with respect to Salicylic Acid. ]
Table 1
Name Relative
Retention
Time
Limit
(%)
Salicylic acid related compound A 0.35 NMT 0.1
Salicylic acid related compound B 0.45 NMT 0.05
Phenol 0.50 NMT 0.02
Other impurity NMT 0.05
Total impurities NMT 0.2
Procedure— Separately inject equal volumes (about 2 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of each relevant related compound taken by the formula:
100(Ci / CU)(ri / rSi)
in which Ci is the concentration, in mg per mL, of the relevant related compound in the Standard solution; CU is the concentration, in mg per mL, of the Test solution; and ri and rSi are the peak responses for the relevant related compounds obtained from the Test solution and the Standard solution, respectively. Calculate the percentage of any other impurity, other than the solvent peak, observed in the chromatogram of the Test solution by the same formula, using the concentration of salicylic acid related compound B in the Standard solution as Ci; the response of the peak of salicylic acid related compound B in the chromatogram obtained from the Standard solution as rSi; and the response of any other impurity as ri. The limits are given in Table 1.
Assay— Dissolve about 500 mg of Salicylic Acid, accurately weighed, in 25 mL of diluted alcohol that previously has been neutralized with 0.1 N sodium hydroxide, add phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS. Each mL of 0.1 N sodium hydroxide is equivalent to 13.81 mg of C7H6O3.
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