pH 7.4 Sodium phosphate buffer— Prepare as directed in the Assay under Cromolyn Sodium.

Assay preparation— Remove and accurately weigh the contents of not fewer than 20 capsules of Cromolyn Sodium Inhalation Powder, and transfer the combined contents to a 250-mL volumetric flask. Dissolve in 100 mL of water, dilute with water to volume, and mix. Transfer an aliquot of this solution, equivalent to 8 mg of cromolyn sodium, to a 250-mL volumetric flask, add 1 mL of pH 7.4 Sodium phosphate buffer, dilute with water to volume, and mix.

Standard preparation— Dissolve a suitable quantity of USP Cromolyn Sodium RS, previously dried in vacuum at 105 to constant weight and accurately weighed, in water to obtain a solution having a known concentration of about 350 µg per mL. Transfer 10 mL of this solution to a 100-mL volumetric flask, add 1 mL of pH 7.4 Sodium phosphate buffer, dilute with water to volume, and mix. The final concentration is about 35 µg per mL.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 326 nm, with a suitable spectrophotometer, using a solution of pH 7.4 Sodium phosphate buffer (1 in 250) as the blank. Calculate the quantity, in mg, of cromolyn sodium (C23H14Na2O11) in the aliquot taken by the formula: in which C is the concentration, in µg per mL, of USP Cromolyn Sodium RS in the Standard preparation; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.