Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

Procedure— Determine the amount of C12H22FeO14·2H2Odissolved,employing atomic absorption spectrophotometry at a wavelength of about 248.3nm 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 C12H22FeO14·2H2Ois dissolved in 45minutes.

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

pH4.6Acetate buffer— Dissolve 3.0g of sodium acetate in 50mLof water,add 2.0mLof glacial acetic acid,dilute with water to 200mL,and mix.

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

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

Standard preparation— Transfer 3.0mLof the Standard stock solutionto a 100-mLvolumetric flask,and add,in the order named,70mLof pH4.6Acetate buffer,10.0mLof sodium thiosulfate solution (1in 10),and 5.0mLof 2,2¢-Bipyridine solution,with mixing following each addition.Heat for 60minutes on a steam bath,cool,dilute with pH4.6Acetate bufferto volume,and mix.The concentration of Fe in the Standard preparationis about 3µg per mL.

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

Assay preparation— Transfer 3.0mLof the Assay stock solutionto a 100-mLvolumetric flask,and proceed as directed for Standard preparation,beginning with “add,in the order named,70mLof pH4.6Acetate buffer.”

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

Procedure— Filter each solution,and concomitantly determine the absorbances of the Standard preparationand the Assay preparationin 1-cm cells at the wavelength of maximum absorbance at about 522nm,with a suitable spectrophotometer,using the Standard preparation blankand 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 482.18is the molecular weight of ferrous gluconate (dihydrate),and 55.85is the atomic weight of iron;Cis the concentration,in µg per mL,of the Standard preparation;and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.