Standard calcium solution —Transfer about 0.33 g of dried calcium carbonate, primary standard grade, accurately weighed, to a 250-mL beaker with the aid of a few mL of water, and dilute with water to about 50 mL. Carefully and dropwise add 2 N hydrochloric acid until all of the solid dissolves, and add 2 drops in excess. Heat the solution to boiling, and boil for 5 minutes. Cool the solution, and transfer to a 1000-mL volumetric flask. Dilute with water to volume, and mix. Calculate the molarity, M, of the solution taken by the formula: in which g is the weight, in g, of calcium carbonate taken.

Standard edetate disodium titrant— Dissolve 10 g of edetate disodium in 100 mL of water. Slowly add alcohol until the first permanent precipitate is formed. Filter, and discard the solid. Add an equal volume of alcohol to the filtrate. Filter the resulting precipitate, discard the filtrate, and wash the residue on the filter, first with acetone, then with ethyl ether. Dry at 80 for 4 days at about 50% relative humidity. Transfer about 3.72 g of this purified edetate disodium, accurately weighed, to a 1000-mL volumetric flask, and dissolve with water. Dilute with water to volume, and mix. Calculate the molarity, MS, of the solution taken by the formula: in which w is the weight, in g, of the purified edetate disodium taken.

Procedure —Transfer 0.15 ± 0.02 g of Cellulose Sodium Phosphate, accurately weighed, to a 250-mL beaker. Add 150.0 mL of Standard calcium solution, and stir the mixture for 5 minutes on a magnetic stirrer. Filter, discarding the first few mL of the filtrate. To 50.0 mL of the filtrate add about 50 mL of water, 15 mL of 1 N sodium hydroxide, and 300 mg of hydroxy naphthol blue. Titrate with Standard edetate disodium titrant to a permanent deep blue color, and designate the number of mL consumed as VS. Calculate the calcium binding capacity of the undried Cellulose Sodium Phosphate, in mmol per g, by the formula: in which W is the weight, in g, of Cellulose Sodium Phosphate taken; and the other terms are as defined above. The calcium binding capacity, calculated on the dried basis, is not less than 1.8 mmol per g.

Standard preparation— Prepare as directed under Inorganic bound phosphate.

Test preparation— Transfer about 2 g of Cellulose Sodium Phosphate, accurately weighed, to a 250-mL beaker. Add 100 mL of water, accurately measured, stir, allow to stand for 5 minutes, stir again, and filter through moderately retentive filter paper, collecting the filtrate in a dry flask.

Procedure— Transfer 2.0 mL of the Standard preparation and 5.0 mL of the Test preparation to separate 100-mL volumetric flasks. Proceed as directed in the Procedure under Inorganic bound phosphate, beginning with “Treat each of these.” Calculate the percentage of free phosphate taken by the formula: in which W is the weight, in mg, of undried Cellulose Sodium Phosphate taken: not more than 3.5%, calculated on the dried basis, is found.

Standard stock solution— Dissolve 508.5 mg of sodium chloride, previously dried at 105 for 2 hours, in 100 mL of water, transfer to a 1000-mL volumetric flask, dilute with water to volume, and mix. Each mL of this solution contains 200 µg of sodium.

Standard preparations— Transfer 5.0, 10.0, 15.0, and 20.0 mL of Standard stock solution to separate 100-mL volumetric flasks, dilute each with water to volume, and mix.

Test preparation— Dissolve about 250 mg of Cellulose Sodium Phosphate, accurately weighed, in 10 mL of a mixture of 20 mL of perchloric acid and 15 mL of nitric acid. Heat cautiously to the production of dense, white fumes, cool, transfer to a 1000-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Concomitantly determine the emission of the Test preparation and of each Standard preparation at the sodium emission line of 589 nm, with a suitable flame photometer. Plot the emissions of the Standard preparations versus their concentration of sodium, and draw a straight line best fitting the four plotted points. From the graph so obtained determine the concentration of sodium in the Test preparation. Calculate the percentage of sodium in the undried Cellulose Sodium Phosphate. The content of sodium, calculated on the dried basis, is not less than 9.5% and not more than 13.0%.

Standard preparation— Transfer 358.2 mg of monobasic potassium phosphate, primary standard grade, to a 250-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Each mL of this solution contains 1.0 mg of phosphate.

Test preparation— Transfer about 250 mg of Cellulose Sodium Phosphate, accurately weighed, to a 250-mL conical flask. Rinse to the bottom with a few mL of water. Add 10 mL of a mixture of 20 mL of perchloric acid and 15 mL of nitric acid. Heat cautiously to the production of dense, white fumes, cool the clear, almost colorless, solution, and transfer to a 100-mL volumetric flask with the aid of water. Dilute with water to volume, and mix.

Procedure— Transfer 2.0-mL portions of the Standard preparation and the Test preparation to separate 100-mL volumetric flasks. Treat each of these and a third flask, providing the blank, as follows: Add 10 mL of 5 N nitric acid, 10.0 mL of ammonium vanadate TS, and about 60 mL of water. Swirl, and add 10.0 mL of a freshly prepared solution of 2.5 g of ammonium molybdate in 50 mL of warm water. Dilute with water to volume, and mix. Concomitantly determine the absorbances, AU and AS, of the solutions from the Standard preparation and the Test preparation, respectively, at 400 nm with a suitable spectrophotometer, using the reagent blank to set the instrument. Calculate the percentage of total phosphate taken by the formula: in which W is the weight, in mg, of Cellulose Sodium Phosphate taken. Calculate the percentage of inorganic bound phosphate in the undried Cellulose Sodium Phosphate by subtracting from this result the percentage of Free phosphate.

(Official January 1, 2007)