Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Times: 1and 3hours.

Standard solution— Transfer the appropriate amount of Iron stock solutionto a volumetric flask,and dilute with 0.1Nhydrochloric acid in such a way that the final concentration is similar to that expected in the solution under test.

Tolerances— The percentages of the labeled amount of Fe (II)dissolved at the times specified conform to Acceptance Table 1under Drug Release á724ñ.

6N Hydrochloric acid— Slowly add 5mLof hydrochloric acid to 5mLof water,and mix.

Diluting solution— Add 1mLof 6N Hydrochloric acidto 59mLof water,and mix.

Phosphoric acid solution— Dilute 20mLof phosphoric acid with Diluting solutionto 200mL,and mix.

Iron stock solution— Transfer about 350mg of ferrous ammonium sulfate hexahydrate,accurately weighed,to a 1000-mLvolumetric flask,dissolve in Diluting solution,dilute with Diluting solutionto volume,and mix to obtain a solution having a known concentration of about 50µg per mL.

Standard preparations— To separate 100-mLvolumetric flasks transfer 2.0,4.0,6.0,8.0,and 10.0mLof Iron stock solution.To each flask add 6.0mLof Phosphoric acid solution,dilute with Diluting solutionto volume,and mix.The Standard preparationsso obtained contain about 1.0,2.0,3.0,4.0,and 5.0µg of iron per mL,respectively.

Blank solution— Transfer 6.0mLof Phosphoric acid solutionto a 100-mLvolumetric flask,dilute with Diluting solutionto volume,and mix.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 1.5g of ferrous fumarate,to a 1000-mLvolumetric flask,add 110mLof 6N Hydrochloric acid,and boil for 30minutes.Cool,dilute with water to volume,mix,and filter.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with Diluting solutionto volume,and mix.Transfer 8.0mLof this solution to a 100-mLvolumetric flask,add 6.0mLof Phosphoric acid solution,dilute with Diluting solutionto volume,and mix to obtain a solution having a known concentration of about 4µg of iron per mL.

Procedure— Concomitantly determine the absorbances of the Standard preparationsand the Assay preparationat the iron emission line at 248.3nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering á851ñ)equipped with an iron hollow-cathode lamp and an air–acetylene flame,using the Blank solutionas the blank.Plot the absorbances of the Standard preparationsversus their concentrations,in µg per mL,of iron,and draw the straight line best fitting the five plotted points.From the graph so obtained,determine the concentration,in µg per mL,of iron in the Assay preparation.Calculate the average quantity,in mg,of ferrous fumarate (C4H2FeO4)in each Tablet taken by the formula: in which Tis the labeled quantity,in mg,of ferrous fumarate in each Tablet;Cis the concentration,in µg per mL,of iron in the Assay preparation;Dis the concentration,in µg per mL,of ferrous fumarate in the Assay preparation,based on the labeled quantity per Tablet and the extent of dilution;and 169.90and 55.85are the molecular weight of ferrous fumarate and the atomic weight of iron,respectively.

Calcium acetate solution— Dissolve 4g of calcium acetate in 2000mLof water.

Diluting solution— Mix 450mLof acetonitrile and 550mLof Calcium acetate solution.

Mobile phase— Add 2mLof phosphoric acid to 1000mLof Diluting solution,and mix.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).Filter,and degas.

Standard preparation— Dissolve an accurately weighed quantity of USP Docusate Sodium RSin Diluting solutionto obtain a solution having a known concentration of about 1mg per mL.

Sodium benzoate solution— Dissolve an accurately weighed quantity of sodium benzoate in Diluting solution,and dilute quantitatively and stepwise with the same solvent to obtain a solution having a known concentration of about 8µg per mL.

Resolution solution— Dissolve a suitable quantity of USP Docusate Sodium RSin Sodium benzoate solutionto obtain a solution containing about 1mg per mLof docusate sodium.

Assay preparation— Transfer a number of Tablets,equivalent to about 2g of docusate sodium,to a 2000-mLvolumetric flask.Add about 1500mLof Diluting solution,and sonicate with frequent shaking until the Tablets are completely disintegrated.Cool,dilute with Diluting solutionto volume,and mix.Centrifuge,and use the clear supernatant layer.If the supernatant layer is not clear,pass through a membrane filter.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 214-nm detector and a 4.6-mm ×30-cm column that contains 3-µm packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Resolution solutionand the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between sodium benzoate and docusate sodium is not less than 7.0;the tailing factor is not less than 0.9and not more than 3.5;the column efficiency is not less than 1000theoretical plates;and the relative standard deviation for six replicate injections of the Standard preparationis not more than 2.0%.The relative retention times are 1.0for docusate sodium and 0.25for sodium benzoate.

Procedure— Separately inject equal volumes (about 25µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the average quantity,in mg,of docusate sodium (C20H37NaO7S)in each of the Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Docusate Sodium RSin the Standard preparation;Nis the number of Tablets taken;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.