A: To 2mLof a dilution of Oral Solution (1in 40)add 5mLof sodium cobaltinitrite TS:a yellow precipitate is formed immediately (presence of potassium).

B: It responds to the test for Citrate á191ñ,3to 5drops of Oral Solution and 20mLof the mixture of pyridine and acetic anhydride being used.

C: It responds to the tests for Ammonium á191ñand for Chloride á191ñ.

Potassium stock solution— Dissolve in water 0.9535g of potassium chloride,previously dried at 105for 2hours.Transfer to a 500-mLvolumetric flask,dilute with water to volume,and mix.This solution contains 1000µg of potassium per mL.

Standard preparations— To separate 200-mLvolumetric flasks transfer 19.0mLand 25.0mL,respectively,of the Potassium stock solution,dilute with water to volume,and mix.The Standard preparationscontain 95.0µg and 125.0µg of potassium per mL,respectively.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 782mg (20mEq)of potassium,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 7.0mLof this solution to a 500-mLvolumetric flask,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 mg,of potassium in each mLof the Oral Solution taken by the formula: in which Vis the volume,in mL,of Oral Solution taken.Each mg of potassium is equivalent to 0.02558mEq.

Ionic strength adjusting solution— Use 5Msodium nitrate.

Procedure— Transfer an accurately measured volume of Oral Solution,equivalent to about 100mg (2.8mEq)of chloride,to a suitable beaker.Add 2.0mLof Ionic strength adjusting solutionand water to make about 100mL,and titrate with 0.1Nsilver nitrate VS,determining the endpoint potentiometrically,using a silver-sulfide specific ion-selective electrode and a double-junction reference electrode containing potassium nitrate solution (1in 10).Perform a blank determination,and make any necessary correction.Each mLof 0.1Nsilver nitrate is equivalent to 3.545mg of chloride (Cl).Each mg of chloride is equivalent to 0.0282mEq of Cl.