4-Aminoantipyrine solution— On the day of use, prepare a solution of 4-aminoantipyrine in water having a concentration of 20 mg per mL.

Potassium ferricyanide solution— On the day of use, prepare a solution of potassium ferricyanide in water having a concentration of 80 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Terbutaline Sulfate RS in water, and dilute quantitatively and stepwise with water to obtain a solution having a known concentration of about 20 µg of terbutaline sulfate per mL.

Test preparation— Discharge the minimum recommended dose into the sampling apparatus and detach the inhaler as directed. Rinse the apparatus (filter and interior) with four 4.0-mL portions of 0.01 N sulfuric acid, and quantitatively transfer the resulting solutions to a 50-mL centrifuge tube. Wash the apparatus (filter and interior) with 10 mL of chloroform, and add the washing to the solution in the centrifuge tube. Wash the apparatus (filter and interior) with 4.0 mL of 0.01 N sulfuric acid, and quantitatively transfer the resulting liquid to the same centrifuge tube. Shake vigorously for 1 minute, and centrifuge for 10 minutes. Use the clear aqueous phase as the Test preparation.

Procedure— Pipet 2 mL of the Test preparation, 2 mL of the Standard preparation, and 2 mL of water to serve as a reagent blank, into separate 1-cm stoppered cells. To each cell add 0.5 mL of 4-Aminoantipyrine solution, and mix. Add 0.5 mL of Potassium ferricyanide solution to each cell, and mix. Thirty seconds, accurately timed, after the addition of the Potassium ferricyanide solution, determine the absorbances of the solutions against the blank, at the wavelength of maximum absorbance at about 550 nm. Calculate the quantity, in µg, of (C12H19NO3)2·H2SO4 contained in the minimum dose taken by the formula: in which C is the concentration, in µg per mL, of USP Terbutaline Sulfate RS in the Standard preparation; N is the number of sprays discharged to obtain the minimum dose; and AU and AS are the absorbances of the solutions from the Test preparation and the Standard preparation, respectively, corrected for the absorbances of the reagent blank solution.

(Official January 1, 2007)

Mobile phase— Prepare a solution containing 750 mL of water, 140 mL of methanol, 110 mL of tetrahydrofuran, and 1.08 g of sodium 1-octanesulfonate. Filter and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Dissolve suitable quantities of USP Terbutaline Sulfate RS and 3,5-dihydroxy--tert-butylaminoacetophenone sulfate in water to obtain a solution containing about 50 and 20 µg per mL, respectively.

Standard preparation— Dissolve an accurately weighed quantity of USP Terbutaline Sulfate RS in water to obtain a solution having a known concentration of about 0.3 mg per mL.

Assay preparation— Accurately weigh not less than three containers, and separately perform the following procedure for each of the units. Chill in a dry ice-acetone mixture to about 75 for 15 to 20 minutes. Quickly and carefully remove the top of the container with a tube cutter. Allow the propellants to evaporate at room temperature for 10 to 15 minutes. [NOTE—Avoid complete evaporation of the propellants.] Quantitatively transfer the suspension to a 500-mL separatory funnel with the aid of chloroform. Wash all parts of the container alternately with several small portions of chloroform followed by small portions of 0.01 N sulfuric acid. Transfer the washings to the separatory funnel, and adjust the phase volumes to about 100 mL each with chloroform and 0.01 N sulfuric acid, respectively. Dry the container and all of its parts at 105 for 1 hour. Cool to room temperature, and weigh. Shake the separatory funnel for 1 minute, allow the phases to separate, and discard the chloroform layer. Filter the acidic aqueous phase through filter paper into a 250-mL volumetric flask. Wash the separatory funnel with two 10-mL portions of water, and transfer the washings to the volumetric flask. Dilute with water to volume, mix, and filter, discarding the first 2 mL of the filtrate.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 280-nm detector and a 6.2-mm × 8-cm column that contains 3-µm packing L7 and is maintained at 40, and fitted with a 0.5-µm pre-column. The flow rate is about 1.5 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.83 and 1.0 for terbutaline and 3,5-dihydroxy--tert-butylaminoacetophenone, respectively; and the resolution, R, between terbutaline sulfate and 3,5-dihydroxy--tert-butylaminoacetophenone is not less than 1.6. Chromatograph the Standard preparation, and record the peak responses as directed in the Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

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 responses for the major peaks. Calculate the quantity, in mg, of (C12H19NO3)2·H2SO4 in each container taken by the formula: in which C is the concentration, in mg per mL, of USP Terbutaline Sulfate RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and Standard preparation, respectively.