A: Infrared Absorption 197K.

B: A solution (1 in 10) responds to the tests for Potassium 191.

Buffer solution— Dissolve 210 g of citric acid monohydrate in 400 mL of water. Adjust with concentrated ammonia to a pH of 7.0, dilute with water to 1000 mL, and mix (Solution A). Dissolve 132 g of dibasic ammonium phosphate in water, dilute with water to 1000 mL, and mix (Solution B). To a suspension of 292 g of edetic acid in about 500 mL of water, add about 200 mL of ammonium hydroxide, and mix to dissolve (Solution C). Adjust with ammonium hydroxide to a pH between 6 and 7, dilute with water to make 1000 mL, and mix. Mix equal volumes of Solution A, Solution B, and Solution C, and adjust with ammonium hydroxide to a pH of 7.5.

Standard stock solution— Weigh accurately about 0.442 g of sodium fluoride, previously dried at 300 for 12 hours, into a 1-L volumetric flask, dilute with water to volume, and mix. Store the solution in a closed plastic container. Immediately before use, pipet 5 mL of this solution into a 100-mL volumetric flask, dilute with water to volume, and mix. Each mL of this solution contains 10 µg of fluoride ion.

Standard solutions— Into separate 50-mL volumetric flasks, pipet 0.5, 1.0, 1.5, and 3.0 mL of the Standard stock solution, add 15.0 mL of Buffer solution to each volumetric flask, dilute with water to volume, and mix.

Test solution— Place about 3 g of Acesulfame Potassium, accurately weighed, in a 50-mL volumetric flask, dissolve in water, add 15.0 mL of Buffer solution, dilute with water to volume, and mix.

Procedure— Concomitantly measure the potential (see Titrimetry 541), in mV, of the Standard solutions and the Test solution, with a suitable pH meter equipped with a fluoride-specific ion electrode and a silver–silver chloride reference electrode. When taking the measurements, transfer the solution to a 25-mL beaker, and immerse the electrodes. Insert a polytef-coated stirring bar into the beaker, place the beaker on a magnetic stirrer having an insulated top, and allow to stir until equilibrium is attained (about 1 to 2 minutes). Rinse, and dry the electrodes between measurements, taking care not to scratch the crystal in the flouride-specific ion electrode. Measure the potential of each Standard solution, and plot the fluoride concentration, in µg per mL, versus the potential, in mV, on semilogarithmic paper. Measure the potential of the Test solution, and determine the fluoride concentration from the standard curve, in µg per mL. Calculate the percentage of fluoride in the portion of Acesulfame Potassium taken by the formula: in which C is the fluoride concentration, in µg per mL, from the standard curve; and W is the weight, in mg, of Acesulfame Potassium taken to prepare the Test solution: not more than 0.0003% of fluoride is found.

Tetrabutylammonium hydrogen sulfate solution— Dissolve 3.3 g of tetrabutylammonium hydrogen sulfate in 1 L of water, and mix.

Mobile phase— Prepare a mixture of Tetrabutylammonium hydrogen sulfate solution and acetonitrile (3:2), filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Dissolve suitable quantities of USP Acesulfame Potassium RS and ethylparaben in water to obtain a solution containing about 2 µg per mL of each.

Standard solution— Dissolve an accurately weighed quantity of USP Acesulfame Potassium RS in water, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 0.2 µg per mL.

Test solution— Transfer about 100 mg of Acesulfame Potassium, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 227-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between acesulfame potassium and ethylparaben is not less than 2.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms for a run time not less than 3 times the retention time of the acesulfame potassium peak, and measure the area responses of the peaks: the response of any peak at a retention time other than that of acesulfame potassium in the chromatogram obtained from the Test solution does not exceed the response of the acesulfame potassium peak in the chromatogram obtained from the Standard solution (0.002%).