Sodium solution— Dissolve in water an accurately weighed quantity of sodium chloride to make a solution containing 5.00mg of sodium per mL.

Standard graph— Into four 1-liter flasks pipet,respectively,0,1,2,and 3mLof Sodium solution.To each flask add 0.1mLof nitric acid,0.1mLof sulfuric acid,and 10mLof low-sodium,low-potassium,nonionic surfactant solution (1in 50),dilute with water to volume,and mix.Adjust the scale of a suitable flame spectrophotometer to a reading of 100at a wavelength of 588nm with the solution containing 15mg of sodium per liter.Determine the instrument readings on the other three solutions,and plot the observed readings,on ruled coordinate paper,as the ordinate,and the concentration of sodium,in mg per liter,as the abscissa.The line intersects the ordinate at,or below,a scale reading of 25(“blank reading”).

Procedure— Ash the equivalent of 1g of Sodium Polystyrene Sulfonate,accurately weighed,with a slight excess of sulfuric acid.Add 1mLof nitric acid and a few mLof water to the residue.Warm to dissolve,and transfer with water to a 1-liter volumetric flask,dilute with water to volume,and mix.Pipet 10mLof this solution into a 100-mLvolumetric flask,add 1mLof low-sodium,low-potassium,non-ionic surfactant solution (1in 50),dilute with water to volume,and mix.Determine the instrument reading concomitantly with the readings obtained for plotting the Standard graph,and determine the sodium concentration,in mg per liter,by interpolation from the Standard graph.Calculate the percentage of sodium taken by the formula: in which Ais the weight,in mg,of sodium found per liter and Wis the weight,in g,of Sodium Polystyrene Sulfonate taken.The sodium content is not less than 9.4%and not more than 11.5%,calculated on the anhydrous basis.

Potassium solution— Dissolve an accurately weighed quantity of potassium chloride in water to make a solution containing 5.00mg of potassium per mL.

Sodium solution— Dissolve an accurately weighed quantity of sodium chloride in water to make a solution containing 4.00mg of sodium per mL.

Standard graph— Identify five 1-liter volumetric flasks by the numbers 1,2,3,4,and 5.In that order pipet into the flasks 4,3,2,1,and 0mL,respectively,of Sodium solution,and in the same order 0,1,2,3,and 4mL,respectively,of Potassium solution.To each flask add 10mLof low-sodium,low-potassium,nonionic surfactant solution (1in 50),dilute with water to volume,and mix.Adjust the scale of a suitable flame spectrophotometer to 100with solution from flask 5at 766nm.Determine the instrument readings with solutions from flasks 4,3,2,and 1.On ruled coordinate paper,plot the observed instrument readings as the ordinate,and the concentrations,in mg per liter,of potassium as the abscissa.

Procedure— Pipet 100mLof Potassium solutioninto a glass-stoppered flask containing about 1.6g of Sodium Polystyrene Sulfonate,accurately weighed,shake by mechanical means for 15minutes,filter,and discard the first 20mLof the filtrate.Pipet 5mLof the filtrate into a 1-liter volumetric flask,add 10mLof low-sodium,low-potassium,nonionic surfactant solution (1in 50),dilute with water to volume,and mix.Observe the flame spectrophotometer readings of the exchanged solution concomitantly with those obtained for plotting the Standard graph,and determine the potassium concentration,in mg per liter,by interpolation from the Standard graph.Calculate the quantity,in mg per g,of potassium adsorbed on the resin taken by the formula: in which Xis the weight,in mg,of potassium in 100mLof Potassium solutionbefore exchange;Yis the weight,in mg,of potassium per liter as interpolated from the Standard graph;and Wis the weight,in g,of Sodium Polystyrene Sulfonate taken,expressed on the anhydrous basis.