Assay for ferrous fumarate
6 N Hydrochloric acid
Slowly add 5 mL of hydrochloric acid to 5 mL of water, and mix.
Diluting solution
Add 1 mL of 6 N Hydrochloric acid to 59 mL of water, and mix.
Phosphoric acid solution
Dilute 20 mL of phosphoric acid with Diluting solution to 200 mL, and mix.
Iron stock solution
Transfer about 350 mg of ferrous ammonium sulfate hexahydrate, accurately weighed, to a 1000-mL volumetric flask, dissolve in Diluting solution, dilute with Diluting solution to volume, and mix to obtain a solution having a known concentration of about 50 µg per mL.
Standard preparations
To separate 100-mL volumetric flasks transfer 2.0, 4.0, 6.0, 8.0, and 10.0 mL of Iron stock solution. To each flask add 6.0 mL of Phosphoric acid solution, dilute with Diluting solution to volume, and mix. The Standard preparations so obtained contain about 1.0, 2.0, 3.0, 4.0, and 5.0 µg of iron per mL, respectively.
Blank solution
Transfer 6.0 mL of Phosphoric acid solution to a 100-mL volumetric flask, dilute with Diluting solution to volume, and mix.
Assay preparation
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 1.5 g of ferrous fumarate, to a 1000-mL volumetric flask, add 110 mL of 6 N Hydrochloric acid, and boil for 30 minutes. Cool, dilute with water to volume, mix, and filter. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Diluting solution to volume, and mix. Transfer 8.0 mL of this solution to a 100-mL volumetric flask, add 6.0 mL of Phosphoric acid solution, dilute with Diluting solution to volume, and mix to obtain a solution having a known concentration of about 4 µg of iron per mL.
Procedure
Concomitantly determine the absorbances of the
Standard preparations and the
Assay preparation at the iron emission line at 248.3 nm with a suitable atomic absorption spectrophotometer (see
Spectrophotometry and Light-scattering 851) equipped with an iron hollow-cathode lamp and an airacetylene flame, using the
Blank solution as the blank. Plot the absorbances of the
Standard preparations versus 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 (C
4H
2FeO
4) in each Tablet taken by the formula:
(TC/D)(169.90/55.85),
in which
T is the labeled quantity, in mg, of ferrous fumarate in each Tablet;
C is the concentration, in µg per mL, of iron in the
Assay preparation; D is 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 169.90 and 55.85 are the molecular weight of ferrous fumarate and the atomic weight of iron, respectively.
Assay for docusate sodium
Calcium acetate solution
Dissolve 4 g of calcium acetate in 2000 mL of water.
Diluting solution
Mix 450 mL of acetonitrile and 550 mL of Calcium acetate solution.
Mobile phase
Add 2 mL of phosphoric acid to 1000 mL of
Diluting solution, and mix. Make adjustments if necessary (see
System Suitability under
Chromatography 621). Filter, and degas.
Standard preparation
Dissolve an accurately weighed quantity of
USP Docusate Sodium RS in
Diluting solution to obtain a solution having a known concentration of about 1 mg 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 8 µg per mL.
Resolution solution
Dissolve a suitable quantity of
USP Docusate Sodium RS in
Sodium benzoate solution to obtain a solution containing about 1 mg per mL of docusate sodium.
Assay preparation
Transfer a number of Tablets, equivalent to about 2 g of docusate sodium, to a 2000-mL volumetric flask. Add about 1500 mL of Diluting solution, and sonicate with frequent shaking until the Tablets are completely disintegrated. Cool, dilute with Diluting solution to volume, and mix. Centrifuge, and use the clear supernatant. If the supernatant is not clear, pass through a membrane filter.
Chromatographic system (see Chromatography 621)
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 1.5 mL per minute. Chromatograph the
Resolution solution and 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 0.9 and not more than 3.5; the column efficiency is not less than 1000 theoretical plates; and the relative standard deviation for six replicate injections of the
Standard preparation is not more than 2.0%. The relative retention times are 1.0 for docusate sodium and 0.25 for sodium benzoate.
Procedure
Separately inject equal volumes (about 25 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the average quantity, in mg, of docusate sodium (C
20H
37NaO
7S) in each of the Tablets taken by the formula:
(2000C/N)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Docusate Sodium RS in the
Standard preparation; N is the number of Tablets taken; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.