A: Two mL, diluted with water to 12 mL, responds to the ferric chloride test for Acetate 191.

B: It responds to the tests for Bicarbonate 191.

C: To 5 mL add 1 mL of hydrochloric acid, and heat to near boiling for 5 minutes to evolve carbon dioxide. Cool, add 1 mL of calcium chloride TS, and render just alkaline to bromothymol blue TS with 1 N sodium hydroxide. Boil for 3 minutes with gentle agitation: a white, crystalline precipitate appears that is insoluble in 1 N sodium hydroxide but dissolves in 3 N hydrochloric acid.

(Official January 1, 2007)

Potassium stock solution— Dissolve, in water, 191 mg of potassium chloride, previously dried at 105 for 2 hours. 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.

Standard preparations— To separate 100-mL volumetric flasks transfer 10.0 mL and 13.0 mL, respectively, of the 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 Standard preparations contain 1.0 µg and 1.3 µg of potassium per mL, respectively.

Assay preparation— Transfer 1.0 mL of Oral Solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 1.0 mL of this solution to a second 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a third 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.

Procedure— Concomitantly determine the absorbances of the Standard preparations and the Assay preparation at the resonance 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 absorbances of the Standard preparations versus concentration, in µg per mL, of potassium. From the graph so obtained, determine the concentration, C, in µg per mL, of potassium in the Assay preparation. Calculate the quantity, in mEq, of potassium in the Oral Solution taken by the formula: in which 39.10 is the atomic weight of potassium.