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: To a mixture of 1mLof Oral Solution with 1mLof hydrochloric acid add 10mLof cobalt-uranyl acetate TS,and stir with a glass rod:no precipitate or turbidity forms after 15minutes,and the solution remains clear (absence of sodium).

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

Potassium stock solution,Sodium stock solution,Lithium diluent solution,and Standard preparation— Prepare as directed in the Assay for sodium and potassiumunder Tricitrates Oral Solution.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 2g of potassium citrate monohydrate,to a 200-mLvolumetric flask,dilute with water to volume,and mix.Transfer 50µLof this solution to a 10-mLvolumetric flask,dilute with Lithium diluent solutionto volume,and mix.

Procedure— Using a suitable flame photometer,adjusted to read zero with Lithium diluent solution,concomitantly determine the potassium flame emission readings for the Standard preparationand the Assay preparationat the wavelength of maximum emission at about 766nm.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 the Potassium stock solution,39.10is the atomic weight of potassium,74.55is the molecular weight of potassium chloride,and RU,Kand RS,Kare the potassium emission readings obtained for the Assay preparationand the Standard 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 the Cation-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 the 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 the Assay for citric acidis equivalent to 1.261mg of C6H5O7.