A: Transfer a portion of Oral Solution, equivalent to about 10 mg of metaproterenol sulfate, to a separator, and extract with four 30-mL portions of ether, discarding the ether extracts. Apply 10 µL of the extracted portion of Oral Solution to the lower right corner of a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture, and allow to dry. Develop the chromatogram in a solvent system consisting of the lower layer of a well-shaken mixture of dioxane, methylene chloride, alcohol, and ammonium hydroxide (4:4:1:1). Allow the solvent front to move about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and dry in vacuum at 35 to 40 for 30 minutes. Rotate the plate 90. At a point about four-fifths of the distance between the initial application of the Oral Solution extract and the solvent front, apply 10 µL of a Standard solution of USP Metaproterenol Sulfate RS in water containing about 2 mg per mL. 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 Oral Solution corresponds to that obtained from the Standard solution.

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

(Official January 1, 2007)

Mobile phase— Mix 10 mL of formic acid and water to make 1000 mL of solution. Filter and degas this solution before use. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Metaproterenol Sulfate RS in water to obtain a solution having a known concentration of about 0.2 mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution, equivalent to about 20 mg of metaproterenol sulfate, to a 100-mL volumetric flask, dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 278-nm detector, a 4.6-mm × 5-cm guard column that contains packing L2, and a 3.9-mm × 30-cm analytical column that contains packing L1. [NOTE—After use, rinse the analytical column with water and store with water in it.] The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor for the analyte peak is not more than 3.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 100 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 quantity, in mg, of metaproterenol sulfate [(C11H17NO3) 2·H2SO4] in each mL of the Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Metaproterenol Sulfate RS in the Standard preparation; V is the volume, in mL, of Oral Solution taken; and rU and rS are the peak responses from the Assay preparation and the Standard preparation, respectively.