Magnesium Salicylate Tablets
» Magnesium Salicylate Tablets contain an amount of magnesium salicylate (C14H10MgO6·4H2O) equivalent to not less than 95.0 percent and not more than 105.0 percent of the labeled amount of C14H10MgO6.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
A: The IR absorption spectrum of a potassium bromide dispersion of a quantity of finely powdered Tablets exhibits maxima at the same wavelengths as that of a similar preparation of USP Magnesium Salicylate RS.
B: A filtered solution of Tablets, equivalent to magnesium salicylate solution (1:20), responds to the test for Magnesium 191.
Medium: water; 900 mL.
Apparatus 2: 50 rpm.
Time: 120 minutes.
Procedure Determine the amount of C14H10MgO6 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 (C14H10MgO6), 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.
Uniformity of dosage units 905: meet the requirements.
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 C14H10MgO6 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.
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USP35NF30 Page 3754