A: Transfer a portion of Oral Solution,equivalent to about 10mg of metaproterenol sulfate,to a separator,and extract with four 30-mLportions of ether,discarding the ether extracts.Apply 10µLof the extracted portion of Oral Solution to the lower right corner of a suitable thin-layer chromatographic plate (see Chromatography á621ñ)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 35to 40for 30minutes.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 10µLof a Standard solution of USP Metaproterenol Sulfate RSin water containing about 2mg per mL.Proceed as directed in Identificationtest Aunder Metaproterenol Sulfate Inhalation Solution,beginning with “Allow the spots to dry”:the RFvalue 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 preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

Mobile phase— Mix 10mLof formic acid and water to make 1000mLof solution.Filter and degas this solution before use.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

Chromatographic system(see Chromatography á621ñ)— 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 2mLper 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 100µL)of the Standard preparationand the Assay preparationinto 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 mLof the Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Metaproterenol Sulfate RSin the Standard preparation;Vis the volume,in mL,of Oral Solution taken;and rUand rSare the peak responses from the Assay preparationand the Standard preparation,respectively.