C14H10MgO6·4H2O 370.59

Magnesium,bis(2-hydroxybenzoato-O1,O2)-,tetrahydrate.
Magnesium salicylate (1:2),tetrahydrate [18917-95-8].

Anhydrous 298.54 [18917-89-0].

Packaging and storage— Store in tight containers.

USP Reference standards á11ñ— USP Magnesium Salicylate RS.USP Salicylic Acid RS.

Identification—

Water,Method Iá921ñ: between 17.5%and 21.0%.

Heavy metals,Method Iá231ñ: 0.004%.

Magnesium content— Transfer about 800mg,accurately weighed,to a 200-mLvolumetric flask.Dissolve in and dilute with water to volume,and mix.Stir the resulting solution continuously for about 15minutes and filter,discarding the first 10mLof the filtrate,into a flask.Transfer 50.0mLof the filtrate to a 250-mLconical flask,add 50mLof water,5mLof ammonia–ammonium chloride buffer TS,and 0.15mLof eriochrome black TS,and titrate with 0.05Medetate disodium VSto a blue endpoint.Each mLof 0.05Medetate disodium is equivalent to 1.215mg of magnesium:between 6.3%and 6.7%of magnesium is found.

Organic volatile impurities,Method Iá467ñ: meets the requirements.

Assay— Transfer 3.0mLof the filtrate prepared in the test for Magnesium contentto a 500-mLvolumetric flask,dilute with water to volume,and mix.Concomitantly determine the absorbances of this solution and a solution of USP Salicylic Acid RSin water having a known concentration of about 18µg per mL,in 1-cm cells at the wavelength of maximum absorbance at about 296nm,with a suitable spectrophotometer,using water as the blank.Calculate the quantity,in mg,of C14H10MgO6·4H2Oin the Magnesium Salicylate taken in the test for Magnesium contentby the formula: in which 370.59is the molecular weight of magnesium salicylate tetrahydrate;276.24is twice the molecular weight of salicylic acid;Cis the concentration,in µg per mL,of USP Salicylic Acid RSin the Standard solution;and AUand ASare the absorbances of the test solution and the Standard solution,respectively.

Expert Committee:(PA2)Pharmaceutical Analysis 2

USP28–NF23Page 1174

Phone Number:1-301-816-8143