A: It responds to the Thin-layer Chromatographic Identification Test 201, the test solution and the Standard solution of USP Isoetharine Hydrochloride RS being prepared at a concentration of 2.5 mg per mL in methanol, the solvent mixture being n-butanol, water, and formic acid (64:25:11), and the spots being located by spraying with sodium hydroxide solution (1 in 10).

B: Mix about 50 mg with about 200 mg of powdered sodium hydroxide, transfer the mixture to a small test tube, heat in a small flame to fusion, and continue the heating for a few minutes longer. Cool, add about 0.5 mL of water, then add a moderate excess of hydrochloric acid, and warm: starch iodate paper placed over the mouth of the test tube turns blue.

Mobile phase— Prepare a filtered and degassed mixture of 0.1 M sodium sulfate in 0.8% acetic acid. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 60 mg of USP Isoetharine Hydrochloride RS, accurately weighed, to a 25-mL volumetric flask, add 4.0 mL of alcohol, and mix. Add 3 drops of 1 N hydrochloric acid, dilute with water to volume, and mix.

Assay preparation— Transfer about 75 mg of Isoetharine Mesylate, accurately weighed, to a 25-mL volumetric flask, add 4.0 mL of alcohol, and mix. Add 3 drops of 1 N hydrochloric acid, dilute with water to volume, and mix.

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 L9. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed under Procedure: the relative standard deviation for replicate injections is not more than 3.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of C13H21NO3·CH4O3S in the portion of Isoetharine Mesylate taken by the formula: in which C is the concentration, in µg per mL, of USP Isoetharine Hydrochloride RS in the Standard preparation; 335.42 and 275.77 are the molecular weights of isoetharine mesylate and isoetharine hydrochloride, respectively; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.