Solution: 1 mg per mL, in 0.1-cm cells. The test solution and the Standard solution contain the equivalent of 1 mg of salicylic acid per mL.

Medium: methanol.

Adsorbent: 0.25-mm layer of chromatographic silica gel mixture.

Test solution— Transfer about 48 mg of Trolamine Salicylate, accurately weighed, to a 50-mL volumetric flask, dilute with xylene to volume, and mix.

Standard solution 1— Dissolve an accurately weighed quantity of USP Salicylic Acid RS in xylene, and dilute quantitatively, and stepwise if necessary, with xylene to obtain a solution having a known concentration of about 0.2 mg per mL.

Standard solution 2— Dilute an accurately measured quantity of Standard solution 1 in xylene to obtain a solution having a known concentration of about 0.1 mg per mL.

Application volume: 5 µL of each solution.

Developing solvent system: a mixture of toluene, acetone, and glacial acetic acid (17:8:0.2).

Procedure— Proceed as directed for Thin-Layer Chromatography under Chromatography 621. Develop in a chamber previously equilibrated with Developing solvent system. Examine the plate under long-wavelength UV light. Any secondary spot obtained from the Test solution is not greater in size or intensity than the spot obtained from Standard solution 1: not more than 0.02% of free salicylic acid is found.

Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay.

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 10 µL) of the Test preparation into the chromatograph, record the chromatogram, and measure all of the peak responses. Calculate the percentage of each impurity in the portion of Trolamine Salicylate taken by the formula: in which ri is the peak response for each impurity, and rs is the sum of the responses of all the peaks: not more than 1.0% of any individual impurity is found, and not more than 2.0% of total impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (7:3). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Salicylic Acid RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 48 µg per mL.

Assay preparation— Transfer a portion of Trolamine Salicylate, equivalent to about 300 mg of salicylic acid, accurately weighed, to a 250-mL volumetric flask, and dilute with methanol to volume. Transfer 2 mL of this solution to a 50-mL volumetric flask, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 308-nm detector and a 4.0-mm × 12.5-cm column that contains packing L1. The flow rate is about 1 mL per minute. The column temperature is maintained at 30. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 8000 theoretical plates; the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of C13H21NO6 in the portion of Trolamine Salicylate taken by the formula: in which rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.