Standard solution— Transfer 2.0 mL of 0.100 N iodine VS to a 500-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Visually examine a portion of the Inhalation Solution (Test solution) in a suitable clear glass test tube against a white background: it is not pinkish, and it contains no precipitate. If any yellow color is observed in the Test solution, concomitantly determine the absorbances of the Test solution and the Standard solution in 1-cm cells with a suitable spectrophotometer set at 460 nm: the absorbance of the Test solution does not exceed that of the Standard solution.

A: Apply 4 µL of the Inhalation Solution and 4 µL of an aqueous solution of USP Metaproterenol Sulfate RS containing about 50 mg per mL to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of the upper layer of a freshly prepared mixture of butyl alcohol, water, and formic acid (50:25:7) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Locate the spots on the plate by examination under short-wavelength UV light: the RF value of the principal spot obtained from the Inhalation Solution corresponds to that obtained from the Standard solution.

B: The chromatogram of the Assay preparation obtained as directed in the Assay exhibits a major peak for metaproterenol, the retention time of which corresponds to that exhibited in the chromatogram of the Standard preparation obtained as directed in the Assay.

Mobile phase, Standard preparation, and Chromatographic system— Prepare as directed in the Assay under Metaproterenol Sulfate.

Assay preparation— Transfer an accurately measured volume of Inhalation Solution, equivalent to about 200 mg of metaproterenol sulfate, to a 100-mL volumetric flask, dilute with 0.01 N hydrochloric acid to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Metaproterenol Sulfate. Calculate the quantity, in mg, of metaproterenol sulfate [(C11H17NO3)2·H2SO4] in each mL of the Inhalation Solution taken by the formula: in which V is the volume, in mL, of Inhalation Solution taken; and C, rU, and rS are as defined therein.