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

Standard edetate disodium titrant— Dissolve 10g of edetate disodium in 100mLof 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 80for 4days at about 50%relative humidity.Transfer about 3.72g of this purified edetate disodium,accurately weighed,to a 1000-mLvolumetric flask,and dissolve with water.Dilute with water to volume,and mix.Calculate the molarity,MS,of the solution taken by the formula: in whichw is the weight,in g,of the purified edetate disodium taken.

Procedure —Transfer 0.15±0.02g of Cellulose Sodium Phosphate,accurately weighed,to a 250-mLbeaker.Add 150.0mLof Standard calcium solution,and stir the mixture for 5minutes on a magnetic stirrer.Filter,discarding the first few mLof the filtrate.To 50.0mLof the filtrate add about 50mLof water,15mLof 1Nsodium hydroxide,and 300mg of hydroxy naphthol blue.Titrate with Standard edetate disodium titrantto a permanent deep blue color,and designate the number of mLconsumed as VS.Calculate the calcium binding capacity of the undried Cellulose Sodium Phosphate,in mmol per g,by the formula: in which Wis 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 1.8mmol per g.

Standard preparation— Prepare as directed under Inorganic bound phosphate.

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

Procedure— Transfer 2.0mLof the Standard preparationand 5.0mLof the Test preparationto separate 100-mLvolumetric flasks.Proceed as directed in the Procedureunder Inorganic bound phosphate,beginning with “Treat each of these.”Calculate the percentage of free phosphate taken by the formula: in which Wis 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 508.5mg of sodium chloride,previously dried at 105for 2hours,in 100mLof water,transfer to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Each mLof this solution contains 200µg of sodium.

Standard preparations— Transfer 5.0,10.0,15.0,and 20.0mLof Standard stock solutionto separate 100-mLvolumetric flasks,dilute each with water to volume,and mix.

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

Procedure— Concomitantly determine the emission of the Test preparationand of each Standard preparationat the sodium emission line of 589nm,with a suitable flame photometer.Plot the emissions of the Standard preparationsversus 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 358.2mg of monobasic potassium phosphate,primary standard grade,to a 250-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Each mLof this solution contains 1.0mg of phosphate.

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

Procedure— Transfer 2.0-mLportions of the Standard preparationand the Test preparationto separate 100-mLvolumetric flasks.Treat each of these and a third flask,providing the blank,as follows:Add 10mLof 5Nnitric acid,10.0mLof ammonium vanadate TS,and about 60mLof water.Swirl,and add 10.0mLof a freshly prepared solution of 2.5g of ammonium molybdate in 50mLof warm water.Dilute with water to volume,and mix.Concomitantly determine the absorbances,AUand AS,of the solutions from the Standard preparationand the Test preparation,respectively,at 400nm with a suitable spectrophotometer,using the reagent blank to set the instrument.Calculate the percentage of total phosphate taken by the formula: in which Wis 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.