Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 2:
50 rpm.
Time:
120 minutes.
Procedure—
Determine the amount of C
14H
10MgO
6 dissolved from UV absorbances at the wavelength of maximum absorbance at about 296 nm of filtered portions of the solution under test, suitably diluted with water, in comparison with a Standard solution having a known concentration of
USP Salicylic Acid RS in the same medium, using water as the blank. Calculate the quantity of magnesium salicylate (C
14H
10MgO
6), dissolved by the formula:
(298.54 / 276.24)(900C)(AU / AS),
in which the terms are as defined in the
Assay.
Tolerances—
Not less than 80% (Q) of the labeled amount of C14H10MgO6 is dissolved in 120 minutes.
Assay—
Weigh and finely powder not fewer than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 500 mg of magnesium salicylate, and transfer to a 250-mL volumetric flask. Dilute with water to volume, mix, and filter, discarding the first 20 mL of the filtrate. Dilute an accurately measured portion of the filtrate quantitatively and stepwise, if necessary, to obtain a final concentration of about 20 µg per mL. Dissolve an accurately weighed quantity of
USP Salicylic Acid RS in water, and dilute quantitatively and stepwise, if necessary, with water to obtain a Standard solution having a known concentration of about 18 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 296 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of C
14H
10MgO
6 in the portion of Tablets taken by the formula:
(298.54 / 276.24)(L / D)(C)(AU / AS),
in which 298.54 is the molecular weight of anhydrous magnesium salicylate; 276.24 is twice the molecular weight of salicylic acid;
L is the labeled quantity, in mg, of magnesium salicylate in each Tablet;
D is the concentration, in mg per mL, of magnesium salicylate in the solution from the Tablets, based on the labeled quantity per Tablet and the extent of dilution;
C is the concentration, in mg per mL, of
USP Salicylic Acid RS in the Standard solution; and
AU and
AS are the absorbances of the solution from the Tablets and the Standard solution, respectively.
