Add the following:

(Official January 1, 2007)

Potassium chloride stock solution— Prepare a solution of potassium chloride, previously dried at 125 for 30 minutes and accurately weighed, in water to obtain a solution having a known concentration of about 7.5 mg per mL.

Sodium chloride stock solution— Prepare a solution of sodium chloride, previously dried at 125 for 30 minutes and accurately weighed, in water to obtain a solution having a known concentration of about 7 mg per mL.

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.

Standard preparation— Transfer 5.0 mL of Potassium chloride stock solution and 5.0 mL of Sodium chloride stock solution to a 50-mL volumetric flask, dilute with water to volume, and mix. Each mL of this intermediate solution contains about 0.75 mg of potassium chloride and 0.7 mg of sodium chloride. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with Lithium diluent solution to volume, and mix.

Assay preparation 1— Weigh and finely powder not fewer than 20 Tablets. [NOTE—Tablets and powder are hygroscopic. After removal from the container, grind the Tablets promptly in an atmosphere of low relative humidity, and weigh the powder promptly.] Transfer an accurately weighed portion of the powder, equivalent to about 3000 mg of potassium bicarbonate, to a 1000-mL volumetric flask, dissolve in 500 mL of water, swirl until effervescence ceases, dilute with water to volume, and mix. Dilute an accurately measured volume of this stock solution quantitatively with water to obtain a test solution containing about 1 mg of potassium bicarbonate per mL, on the basis of the labeled quantity. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with Lithium diluent solution to volume, and mix.

Assay preparation 2— Dilute an accurately measured volume of the stock solution used to prepare Assay preparation 1 quantitatively with water to obtain a test solution containing about 1 mg of sodium bicarbonate per mL, on the basis of the labeled quantity. Transfer 5.0 mL of this solution to a 100-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 potassium flame emission readings for the Standard preparation and Assay preparation 1 at the wavelength of maximum emission at about 766 nm. Calculate the quantity, in mg, of potassium bicarbonate (KHCO3) in each Tablet taken by the formula: in which 100.12 and 74.55 are the molecular weights of potassium bicarbonate and potassium chloride, respectively; L is the labeled quantity, in mg, of potassium bicarbonate in each Tablet; C is the concentration, in mg per mL, of potassium chloride in the intermediate solution used to prepare the Standard preparation; D is the concentration, in mg per mL, of potassium bicarbonate in the test solution used to prepare Assay preparation 1, on the basis of the labeled quantity of potassium bicarbonate in each Tablet and the extent of dilution; and RU,K and RS,K are the potassium emission readings obtained from Assay preparation 1 and the Standard preparation, respectively. Similarly determine the sodium flame emission readings for the Standard preparation and Assay preparation 2 at the wavelength of maximum emission at about 589 nm. Calculate the quantity, in mg, of sodium bicarbonate (NaHCO3) in each Tablet taken by the formula: in which 84.01 and 58.44 are the molecular weights of sodium bicarbonate and sodium chloride, respectively; L is the labeled quantity, in mg, of sodium bicarbonate in each Tablet; C is the concentration, in mg per mL, of sodium chloride in the intermediate solution used to prepare the Standard preparation; D is the concentration, in mg per mL, of sodium bicarbonate in the test solution used to prepare Assay preparation 2, on the basis of the number of Tablets taken, the labeled quantity of sodium bicarbonate in each Tablet, and the extent of dilution; and RU,Na and RS,Na are the sodium emission readings obtained from Assay preparation 2 and the Standard preparation, respectively.

Cation-exchange column— Mix 10 g of styrenedivinylbenzene 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 14-mm × 30-cm glass chromatographic tube (having a sealed-in, coarse-porosity porous glass 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— Transfer an accurately measured volume of the stock solution used to prepare Assay preparation 1 in the Assay for potassium bicarbonate and sodium bicarbonate, equivalent to about 40 mg of anhydrous citric acid, 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 the eluate in a suitable flask. Boil the eluate for 1 minute, cool, add 5 drops of phenolphthalein TS, swirl the flask, and titrate with 0.02 N sodium hydroxide VS to a pink endpoint. Each mL of 0.02 N sodium hydroxide is equivalent to 1.281 mg of anhydrous citric acid (C6H8O7).

(Official until January 1, 2009)

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— Transfer an accurately measured volume of the stock solution used to prepare Assay preparation 1 in the Assay for potassium bicarbonate and sodium bicarbonate, equivalent to about 40 mg of anhydrous citric acid, 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 quantity, in mg, of anhydrous citric acid (C6H8O7) in the portion of Tablets taken by the formula: in which 192.12 is the molecular weight of anhydrous citric acid; 189.10 is the molecular weight of citrate (C6H5O7); CS is the concentration, in µg per mL, of citrate in Standard Preparation 1; D is the dilution factor; and rU and rS are the citrate peak areas obtained from the Assay preparation and Standard Preparation 1, respectively.USP29