(me tir' a pone).
» Metyrapone contains not less than 98.0 percent and not more than 102.0 percent of C14H14N2O, calculated on the dried basis.
Packaging and storage Preserve in tight containers, protected from heat and light.
USP Reference standards 11
B: Ultraviolet Absorption 197U
Solution: 10 µg per mL.
Medium: 1 N sulfuric acid.
Loss on drying 731 Dry it in vacuum at room temperature for 6 hours: it loses not more than 0.5% of its weight.
Residue on ignition 281: not more than 0.1%.
Heavy metals, Method II 231: 0.001%.
Standard solutions Dissolve USP Metyrapone RS in methanol, and mix to obtain a solution having a known concentration of 0.2 mg per mL. Dilute quantitatively with methanol to obtain Standard solution A, containing 40 µg of the Reference Standard per mL, and Standard solution B, containing 20 µg of the Reference Standard per mL.
Test solution Dissolve an accurately weighed quantity of Metyrapone in methanol to obtain a solution containing 20 mg per mL.
Procedure Apply separately 5 µL of the Test solution and 5 µL of each Standard solution to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of chloroform and methanol (48:3) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and dry under a current of nitrogen for about 10 minutes. Position the dried plate once again in the same chromatographic chamber, and again develop the chromatograms, until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and dry under a current of warm air for about 15 minutes. Examine the plate under short-wavelength UV light, and compare the intensities of any secondary spots observed in the chromatogram of the Test solution with those of the principal spots in the chromatograms of the Standard solutions: no secondary spot from the chromatogram of the Test solution is larger or more intense than the principal spot obtained from Standard solution A (0.2%), and the sum of the intensities of the secondary spots obtained from the Test solution corresponds to not more than 1.0%.
Assay Transfer about 50 mg of Metyrapone, accurately weighed, to a 100-mL volumetric flask. Dissolve in 1 N sulfuric acid, dilute with the same solvent to volume, and mix. Pipet 2 mL of this solution into a 100-mL volumetric flask, add 1 N sulfuric acid to volume, and mix. Dissolve an accurately weighed quantity of USP Metyrapone RS in 1 N sulfuric acid, and dilute quantitatively and stepwise with 1 N sulfuric acid to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 260 nm, with a suitable spectrophotometer, using 1 N sulfuric acid as the blank. Calculate the quantity, in mg, of C14H14N2O in the portion of Metyrapone taken by the formula:
5C(AU / AS)in which C is the concentration, in µg per mL, of USP Metyrapone RS in the Standard solution, and AU and AS are the absorbances of the solution of Metyrapone and the Standard solution, respectively.
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USP35NF30 Page 3910