Add the following:

A: It responds to the flame test for Sodium 191.

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

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

D: It responds to the tests for Citrate 191, 3 to 5 drops of Oral Solution and 20 mL of the mixture of pyridine and acetic anhydride being used.

(Official January 1, 2007)

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

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

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

Standard preparation— Pipet 50 mL of Sodium stock solution and 50 mL of Potassium stock solution into a 500-mL volumetric flask, dilute with water to volume, and mix. Each mL of this solution contains 0.1 mEq of Na and 0.1 mEq of K. Transfer 50 µL of this solution to a 10-mL volumetric flask, dilute with Lithium diluent solution to volume, and mix.

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

Procedure— Using a suitable flame photometer, adjusted to read zero with Lithium diluent solution, concomitantly determine the sodium flame emission readings for the Standard preparation and the Assay preparation at the wavelength of maximum emission at about 589 nm. Similarly determine the potassium flame emission readings for the same solutions at the wavelength of maximum emission at about 766 nm. Calculate the quantity, in g, of Na in the portion of Oral Solution taken by the formula: in which 14.61 is the weight, in g, of sodium chloride in the Sodium stock solution; 22.99 is the atomic weight of sodium; 58.44 is the molecular weight of sodium chloride; and RU,Na and RS,Na are the sodium emission readings obtained for the Assay preparation and the Standard preparation, respectively. Calculate the quantity, in g, of K in the portion of Oral Solution taken by the formula: in which 18.64 is the weight, in g, of potassium chloride in the Potassium stock solution; 39.10 is the atomic weight of potassium; 74.55 is the molecular weight of potassium chloride; and RU,K and RS,K are the potassium emission readings obtained from the Assay preparation and the Standard preparation, respectively.

Cation-exchange column— Mix 10 g of styrene-divinylbenzene cation-exchange resin with 50 mL of 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 100 mL of water, closing the stopcock when the water level is about 2 mm above the resin bed.

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

Change to read:

Mobile phase, Standard Preparation 1, and Chromatographic System— Proceed as directed under Assay for Citric Acid/Citrate and Phosphate 345.

Assay preparation— Pipet 15 mL of Oral Solution into a suitable volumetric flask, and proceed as directed for Assay Preparation for Citric Acid/Citrate Assay under Assay for Citric Acid/Citrate and Phosphate 345.

Procedure— Proceed as directed for Procedure under 345, and calculate the concentration, in mg per mL, of citrate (C6H5O7) in the Oral Solution taken by the formula: in which CS is the concentration, in µg per mL, of citrate in Standard Preparation 1; D is the dilution factor; V is the volume of Oral Solution used in the preparation of the Assay preparation; rU and rS are the citrate peak areas obtained from the Assay preparation and Standard Preparation 1, respectively; 189.10 is the molecular weight of citrate (C6H5O7); 210.14 is the molecular weight of citric acid monohydrate (C6H8O7 · H2O); and A is the concentration of citric acid monohydrate, in mg per mL, determined in the Assay for citric acid.USP29