Sodium solution and Standard graph— Prepare as directed in the test for Sodium content under Sodium Polystyrene Sulfonate.

Procedure— Transfer an accurately measured quantity of Suspension, freshly mixed and free from air bubbles, equivalent to about 1 g of sodium polystyrene sulfonate, to a suitable crucible, heat at 80 until dry, and ash the residue with a slight excess of sulfuric acid. Proceed as directed for Procedure in the test for Sodium content under Sodium Polystyrene Sulfonate, beginning with “Add 1 mL of nitric acid.” Calculate the percentage of sodium taken by the formula: in which A is the quantity, in mg, of sodium found per liter, and L is the quantity, in g, of sodium polystyrene sulfonate in the portion of Suspension taken, based on the labeled amount: the sodium content is not less than 9.4% and not more than 11.5%.

Potassium solution, Sodium solution, and Standard graph— Prepare as directed in the test for Potassium exchange capacity under Sodium Polystyrene Sulfonate.

Procedure— Transfer an accurately measured quantity of Suspension, freshly mixed and free from air bubbles, equivalent to about 1.6 g of sodium polystyrene sulfonate, to a suitable glass-stoppered flask, add 100.0 mL of Potassium solution, shake by mechanical means for 15 minutes, filter, and discard the first 20 mL of the filtrate. Proceed as directed for Procedure in the test for Potassium exchange capacity under Sodium Polystyrene Sulfonate, beginning with “Pipet 5 mL of the filtrate.” Calculate the quantity, in mg, of potassium adsorbed on each g of the sodium polystyrene sulfonate taken by the formula: in which X is the quantity, in mg, of potassium in 100 mL of Potassium solution before exchange; Y is the quantity, in mg, of potassium per L as interpolated from the Standard graph; and L is the labeled quantity, in g, of sodium polystyrene sulfonate in the portion of Suspension taken.

(Official January 1, 2007)

Mobile phase, Resolution solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Sorbitol (see NF monograph).

Assay preparation— Dilute an accurately measured volume of Suspension, freshly mixed and free from air bubbles, quantitatively with water to obtain a solution containing about 4.8 mg of sorbitol per mL. Filter, and use the filtrate as the Assay preparation.

Procedure— Separately inject equal volumes (about 20 µL) of the Assay preparation and the Standard preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Proceed as directed for Procedure in the Assay under Sorbitol (see NF monograph). Calculate the quantity, in g, of C6H14O6, in each mL of the Suspension taken by the formula: in which L is the labeled quantity, in g, of sorbitol in each mL of Suspension; D is the quantity, in mg, of sorbitol in each mL of the Assay preparation based on the labeled quantity and the extent of dilution; C is the concentration, in mg per mL, of USP Sorbitol RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.