Standard preparation— Prepare as directed in the Assay under Fluorescein Sodium.

Assay preparation— Remove 1 Strip from its package, taking care not to allow any portion of the tip to adhere to the packaging material, transfer to a 100-mL volumetric flask, add 50 mL of water, shake the flask vigorously, and dilute with water to volume. Shake occasionally, and, after 1 hour, mix the contents of the flask. Transfer an aliquot (V) of this solution, equivalent to about 100 µg of fluorescein sodium, to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 3 mL of the resulting solution to a 100-mL volumetric flask containing 20 mL of pH 9.0 alkaline borate buffer (see Buffer Solutions in the section Reagents, Indicators, and Solutions), dilute with water to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Fluorescein Sodium. Calculate the quantity, in mg, of fluorescein sodium (C20H10Na2O5) in the Strip taken by the formula: in which C is the concentration, in µg per mL, of fluorescein sodium in the Standard preparation; V is the volume of the aliquot of solution taken for the Assay preparation; and IU and IS are the fluorescence intensities observed for the Assay preparation and the Standard preparation, respectively. Calculate the average content from the individual assays of not less than 10 Strips.