(meth'' oh hex' i tal).
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C14H18N2O3 262.30

2,4,6(1H,3H,5H)-Pyrimidinetrione, 1-methyl-5-(1-methyl-2-pentynyl)-5-(2-propenyl)-, (±)-.
(±)-5-Allyl-1-methyl-5-(1-methyl-2-pentynyl)barbituric acid [18652-93-2].
» Methohexital contains not less than 98.0 percent and not more than 101.0 percent of C14H18N2O3, calculated on the anhydrous basis.
Packaging and storage— Preserve in well-closed containers.
USP Reference standards 11
USP Methohexital RS Click to View Structure
Identification, Infrared Absorption 197S
Solution: 1 in 100.
Medium: chloroform.
Melting range 741: between 92 and 96, but the range between beginning and end of melting does not exceed 3.
Water, Method I 921: not more than 2.0%.
Chloride 221 Dissolve 200 mg in a mixture of 75 mL of ether and 25 mL of water, agitate, and allow to separate: the water solution shows no more chloride than corresponds to 0.17 mL of 0.010 N hydrochloric acid (0.03%).
Ordinary impurities 466
Test solution: methanol.
Standard solution: methanol.
Eluant: a mixture of chloroform and acetone (7:3).
Visualization— Expose the plate to chlorine gas for 1 minute, and air-dry the plate at room temperature for 2 minutes. Prepare a solution of 0.5 g of potassium iodide in 50 mL of water, and prepare a solution of 1.5 g of soluble starch in 50 mL of hot water. Mix 10 mL of each solution with 4 mL of alcohol to obtain the Detection reagent. [note—The Detection reagent so obtained may be used for up to 3 or 4 days. ] Spray the plate with the Detection reagent.
Assay— Dissolve about 100 mg of Methohexital, accurately weighed, in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a solution having a concentration of about 10 mg per mL. Dissolve an accurately weighed quantity of USP Methohexital RS in chloroform, and dilute quantitatively and stepwise with chloroform to obtain a Standard solution having a known concentration of about 10 mg per mL. Concomitantly determine the absorbances of both solutions in 0.1-mm cells at the wavelength of maximum absorbance at about 5.93 µm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of C14H18N2O3 in the portion of Methohexital taken by the formula:
10C(AU / AS)
in which C is the concentration, in mg per mL, of USP Methohexital RS in the Standard solution; and AU and AS are the absorbances of the solution of Methohexital and the Standard solution, respectively.
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Reference Standards RS Technical Services
USP35–NF30 Page 3853
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