A: Powder a number of Tablets, equivalent to about 100 mg of metaproterenol sulfate, add 10 mL of water, stir for about 3 minutes, and centrifuge. Use the clear solution so obtained as the Test solution. Dissolve a suitable quantity of USP Metaproterenol Sulfate RS in water to obtain a Standard solution having a concentration of 10 mg per mL. Apply separate 10-µL portions of the Test solution and the Standard solution to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Proceed as directed in Identification test A under Metaproterenol Sulfate Inhalation Solution, beginning with “Allow the spots to dry”: the RF value of the principal spot obtained from the Test solution corresponds to that obtained from the Standard solution.

B: Mix a quantity of powdered Tablets, equivalent to about 20 mg of metaproterenol sulfate, with 5 mL of water, and filter: the filtrate responds to the tests for Sulfate 191.

C: 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.

Medium: water; 500 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of (C11H17NO3)2·H2SO4 dissolved from UV absorbances at the wavelength of maximum absorbance at about 276 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Metaproterenol Sulfate RS in the same Medium.

Tolerances— Not less than 70% (Q) of the labeled amount of (C11H17NO3)2·H2SO4 is dissolved in 30 minutes.

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

Assay preparation— Transfer 20 Tablets to a 500-mL conical flask. Add an accurately measured volume of 0.01 N hydrochloric acid sufficient to yield a solution containing about 2 mg of metaproterenol sulfate per mL, shake by mechanical means for 30 minutes, and filter. Use the filtrate so obtained as the Assay preparation.

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 Tablet taken by the formula: in which V is the volume, in mL, of 0.01 N hydrochloric acid added; and C, rU, and rS are as defined therein.