15 N Formic acid— To a 1-L volumetric flask, add approximately 300 mL of water, then weigh 719 g of 96% formic acid into this flask, and mix. Cool the solution to 20. Dilute with water to volume, and mix.

Test solution: 62 mg per mL, in 15 N Formic acid.

Potassium stock solution— Dissolve an accurately weighed quantity of about 190 mg of potassium chloride, previously dried at 105 for 2 hours, in water. Transfer to a 1000-mL volumetric flask, dilute with water to volume, and mix. Transfer 100.0 mL of this solution to a second 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains 10 µg of potassium per mL.

Reference solutions— To three identical 100-mL volumetric flasks transfer 10.0, 15.0, and 20.0 mL, respectively, of Potassium stock solution. To each flask add 2.0 mL of sodium chloride solution (1 in 5) and 1.0 mL of hydrochloric acid, dilute with water to volume, and mix. The Reference solutions contain, respectively, 1.0, 1.5, and 2.0 µg of potassium per mL.

Test solution— Transfer about 1.5 g of Aspartame Acesulfame, accurately weighed, to a 500-mL volumetric flask, dilute with water to volume, and mix. Transfer 10 mL of this solution to a 100-mL volumetric flask, add 2.0 mL of sodium chloride solution (1 in 5) and 1.0 mL of hydrochloric acid, dilute with water to volume, and mix. Filter the solution.

Procedure— Concomitantly determine the absorbances of the Reference solutions and the Test solution at the potassium emission line of 766.5 nm, with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a potassium hollow-cathode lamp and an air–acetylene flame, using water as the blank. Plot the absorbance of the Reference solutions versus concentration, in µg per mL, of potassium, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, C, in µg per mL, of potassium in the Test solution. Calculate the percentage of potassium in the portion of Aspartame Acesulfame taken by the formula: in which W is the quantity, in mg, of Aspartame Acesulfame taken to prepare the Test solution: not more than 0.5% is found.

Diluent— Prepare a mixture of water and methanol (9:1).

Mobile phase— Prepare a filtered and degassed solution by dissolving 5.6 g of monobasic potassium phosphate in 820 mL of water in a 1-liter volumetric flask, adjusting with phosphoric acid to a pH of 4.3, diluting with methanol to volume, and mixing. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of USP Aspartame Related Compound A RS in Diluent, and quantitatively dilute with Diluent to obtain a solution having a known concentration of about 25 µg per mL.

Test solution— Transfer 50 mg of Aspartame Acesulfame, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. [note—Avoid heat and excessive holding times.]

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and 4.6-mm × 25-cm column containing packing L1. The flow rate is about 1.5 mL per minute. The column temperature is maintained at 40. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; and the relative standard deviation for replicate injections is not more than 4.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of aspartame related compound A in the portion of Aspartame Acesulfame taken by the formula: in which C is the concentration, in µg per mL, of USP Aspartame Related Compound A RS in the Standard solution; W is the weight, in mg, of Aspartame Acesulfame, taken to prepare the Test solution; and rU and rS are the peak responses of aspartame related compound A obtained from the Test solution and the Standard solution, respectively: not more than 0.5% is found.

Diluent, Mobile phase, Test solution, and Chromatographic system— Proceed as directed for Related compounds.

Acesulfame solution— Transfer about 20 mg of USP Acesulfame Potassium RS to a 10-mL volumetric flask, dilute with Diluent to volume, and mix.

Diluted test solution— Pipet 1.5 mL of the Test solution into a 100-mL volumetric flask, dilute with Diluent to volume, and mix.

Procedure— Inject equal volumes (about 20 µL) of the Acesulfame solution, the Diluted test solution, and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. [note—Continue the elution of the Test solution for twice the retention time of the aspartame peak.] The sum of the responses of all the peaks in the chromatogram of the Test solution, excluding the aspartame related compound A, acesulfame, and aspartame peak responses, is not greater than the aspartame peak response obtained from the Diluted test solution (1.0%).

163N(V1 – VB)/(10W) (1)

294N(V2 – V1)/(10W) (2)