Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C12H22FeO14·2H2O dissolved, employing atomic absorption spectrophotometry at a wavelength of about 248.3 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of iron in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C12H22FeO14·2H2O is dissolved in 45 minutes.

2,2¢-Bipyridine solution— Dissolve 400 mg of 2,2¢-bipyridine in 100 mL of water, using heat, if necessary, to effect solution. Cool, and filter.

pH 4.6 Acetate buffer— Dissolve 3.0 g of sodium acetate in 50 mL of water, add 2.0 mL of glacial acetic acid, dilute with water to 200 mL, and mix.

Standard stock solution— Transfer an amount of ferrous ammonium sulfate, equivalent to 702.2 mg of ferrous ammonium sulfate hexahydrate [Fe(NH4)2(SO4)2·6H2O] to a 100-mL volumetric flask, dissolve and dilute with water to volume, and mix. Transfer 10.0 mL of the solution to a second 100-mL volumetric flask, add 5 mL of 2 N sulfuric acid, dilute with water to volume, and mix. This solution contains 100 µg of iron (Fe) per mL.

Assay stock solution for hard gelatin capsules— Transfer, as completely as possible, the contents of not fewer than 20 Capsules to a suitable tared container. Mix and finely powder the combined contents, and transfer an accurately weighed portion of the powder, equivalent to about 430 mg of ferrous gluconate, to a 500-mL volumetric flask. Add about 300 mL of water, mix, heat on a steam bath, if necessary, to dissolve, cool, dilute with water to volume, and mix.

Assay stock solution for soft gelatin capsules— Place a number of Capsules, equivalent to about 430 mg of ferrous gluconate, in a 500-mL volumetric flask. Add about 300 mL of water, heat on a steam bath to dissolve the Capsules, cool, dilute with water to volume, and mix.

Standard preparation— Transfer 3.0 mL of the Standard stock solution to a 100-mL volumetric flask, and add, in the order named, 70 mL of pH 4.6 Acetate buffer, 10.0 mL of sodium thiosulfate solution (1 in 10), and 5.0 mL of 2,2¢-Bipyridine solution, with mixing following each addition. Heat for 60 minutes on a steam bath, cool, dilute with pH 4.6 Acetate buffer to volume, and mix. The concentration of Fe in the Standard preparation is about 3 µg per mL.

Standard preparation blank— Proceed as directed for Standard preparation, but omit the addition of 5.0 mL of 2,2¢-Bipyridine solution.

Assay preparation— Transfer 3.0 mL of the Assay stock solution to a 100-mL volumetric flask, and proceed as directed for Standard preparation, beginning with “add, in the order named, 70 mL of pH 4.6 Acetate buffer.”

Assay preparation blank— Proceed as directed for Assay preparation, but omit the addition of 5.0 mL of 2,2¢-Bipyridine solution.

Procedure— Filter each solution, and concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 522 nm, with a suitable spectrophotometer, using the Standard preparation blank and the Assay preparation blank, respectively, to set the instrument. Calculate the quantity, in mg, of ferrous gluconate (C12H22FeO14·2H2O) in the portion of Capsules taken by the formula: in which 482.18 is the molecular weight of ferrous gluconate (dihydrate), and 55.85 is the atomic weight of iron; C is the concentration, in µg per mL, of the Standard preparation; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.