A: It responds to the flame test forSodium á191ñ.

B: Add 2mLof a solution of anhydrous potassium carbonate (15in 100)to 2mLof Oral Solution,boil,and cool.Add 4mLof potassium pyroantimonate TS:a dense precipitate is formed (presence of sodium).

C: To 2mLof a dilution of Oral Solution (1in 20)add 5mLof sodium cobaltinitrite TS:a yellow precipitate is formed immediately (presence of potassium).

D: It responds to the tests forCitrate á191ñ,3to 5drops of Oral Solution and 20mLof the mixture of pyridine and acetic anhydride being used.

Sodium stock solution— Transfer 14.61g of sodium chloride,previously dried at 105for 2hours and accurately weighed,to a 250-mLvolumetric flask,add water to volume,and mix.

Potassium stock solution— Transfer 18.64g of potassium chloride,previously dried at 105for 2hours and accurately weighed,to a 250-mLvolumetric flask,add water to volume,and mix.

Lithium diluent solution— Transfer 1.04g of lithium nitrate to a 1000-mLvolumetric flask,add a suitable nonionic surfactant,then add water to volume,and mix.This solution contains 15mEq of Li per 1000mL.

Standard preparation— Pipet 50mLofSodium stock solution and 50mLofPotassium stock solution into a 500-mLvolumetric flask,dilute with water to volume,and mix.Each mLof this solution contains 0.1mEq of Na and 0.1mEq of K.Transfer 50µLof this solution to a 10-mLvolumetric flask,dilute withLithium diluent solution to volume,and mix.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 2g of combined citrates,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 50µLof this solution to a 10-mLvolumetric flask,dilute withLithium diluent solution to volume,and mix.

Procedure— Using a suitable flame photometer,adjusted to read zero withLithium diluent solution,concomitantly determine the sodium flame emission readings for theStandard preparation and theAssay preparation at the wavelength of maximum emission at about 589nm.Similarly determine the potassium flame emission readings for the same solutions at the wavelength of maximum emission at about 766nm.Calculate the quantity,in g,of Na in the portion of Oral Solution taken by the formula: in which 14.61is the weight,in g,of sodium chloride in theSodium stock solution,22.99is the atomic weight of sodium,58.44is the molecular weight of sodium chloride,andRU,NaandRS,Naare the sodium emission readings obtained for theAssay preparation and theStandard preparation,respectively.Calculate the quantity,in g,of Kin the portion of Oral Solution taken by the formula: in which 18.64is the weight,in g,of potassium chloride in thePotassium stock solution,39.10is the atomic weight of potassium,74.55is the molecular weight of potassium chloride,andRU,KandRS,Kare the potassium emission readings obtained from theAssay preparation and theStandard preparation,respectively.

Cation-exchange column— Mix 10g of styrene-divinylbenzene cation-exchange resin with 50mLof water in a suitable beaker.Allow the resin to settle,and decant the supernatant until a slurry of resin remains.Pour the slurry into a 15-mm ×30-cm glass chromatographic tube (having a sealed-in,coarse-porosity fritted disk and fitted with a stopcock),and allow to settle as a homogeneous bed.Wash the resin bed with about 100mLof water,closing the stopcock when the water level is about 2mm above the resin bed.

Procedure— Pipet 15mLof Oral Solution into a 250-mLvolumetric flask,dilute with water to volume,and mix.Pipet 5mLof this solution carefully onto the top of the resin bed in theCation-exchange column.Place a 250-mLconical flask below the column,open the stopcock,and allow to flow until the solution has entered the resin bed.Elute the column with 60mLof water at a flow rate of about 5mLper minute,collecting about 65mLof eluate.Add 5drops of phenolphthalein TSto the eluate,swirl the flask,and titrate with 0.02Nsodium hydroxide VS.Record the buret reading,and calculate the volume (B)of 0.02Nsodium hydroxide consumed.Each mLof the difference between the volume (B)and the volume (A)of 0.02Nsodium hydroxide consumed in theAssay for citric acid is equivalent to 1.261mg of C6H5O7.