A: Two mL,diluted with water to 12mL,responds to the ferric chloride test for Acetate á191ñ.

B: It responds to the tests for Bicarbonate á191ñ.

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

Potassium stock solution— Dissolve,in water,191mg of potassium chloride,previously dried at 105for 2hours.Transfer to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Transfer 100.0mLof this solution to a second 1000-mLvolumetric flask,dilute with water to volume,and mix.This solution contains 10µg of potassium per mL.

Standard preparations— To separate 100-mLvolumetric flasks transfer 10.0mLand 13.0mL,respectively,of the Potassium stock solution.To each flask add 2.0mLof sodium chloride solution (1in 5)and 1.0mLof hydrochloric acid,dilute with water to volume,and mix.The Standard preparationscontain 1.0µg and 1.3µg of potassium per mL,respectively.

Assay preparation— Transfer 1.0mLof Oral Solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 1.0mLof this solution to a second 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a third 100-mLvolumetric flask,add 2.0mLof sodium chloride solution (1in 5)and 1.0mLof hydrochloric acid,dilute with water to volume,and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparationsand the Assay preparationat the resonance line of 766.5nm,with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering á851ñ)equipped with a potassium hollow-cathode lamp and an air–acetylene flame,using water as the blank.Plot the absorbances of the Standard preparationsversus 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 39.10is the atomic weight of potassium.