(en flur' ane).
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C3H2ClF5O 184.49

Ethane, 2-chloro-1-(difluoromethoxy)-1,1,2-trifluoro-, (±)-.
(±)-2-Chloro-1,1,2-trifluoroethyl difluoromethyl ether [13838-16-9].
» Enflurane contains not less than 99.9 percent and not more than 100.0 percent of C3H2ClF5O.
Packaging and storage— Preserve in tight, light-resistant containers, and avoid exposure to excessive heat.
USP Reference standards 11
USP Enflurane RS Click to View Structure
Identification— The IR absorption spectrum of a thin film of it exhibits maxima only at the same wavelengths as that of a similar preparation of USP Enflurane RS.
Specific gravity 841: not less than 1.516 and not more than 1.519.
Refractive index 831: not less than 1.3020 and not more than 1.3038 at 20.
Acidity or alkalinity— Shake 20 mL with 20 mL of carbon dioxide-free water for 3 minutes, and allow the layers to separate: the aqueous layer requires not more than 0.10 mL of 0.010 N sodium hydroxide or not more than 0.60 mL of 0.010 N hydrochloric acid for neutralization, bromocresol purple TS being used as the indicator.
Water, Method I 921: not more than 0.14%.
Limit of nonvolatile residue— Allow 10.0 mL to evaporate at room temperature in a tared evaporating dish, and dry the residue at 50 for 2 hours: the weight of the residue does not exceed 2 mg.
Chloride 221 Shake 25 mL with 25 mL of water for 5 minutes, and allow the liquids to separate completely. Draw off the water layer, and add to it 1 drop of nitric acid and 5 drops of silver nitrate TS: any turbidity produced is no greater than that produced in a solution containing 0.35 mL of 0.020 N hydrochloric acid.
Limit of fluoride ions— [note—Use plasticware throughout this test. ]
pH 5.25 buffer— Dissolve 110 g of sodium chloride and 1 g of sodium citrate in 700 mL of water in a 2000-mL volumetric flask. Cautiously add 150 g of sodium hydroxide, and dissolve with shaking. Cool to room temperature, and, while stirring, cautiously add 450 mL of glacial acetic acid to the cooled solution. Cool, add 600 mL of isopropyl alcohol, dilute with water to volume, and mix: the pH of this solution is between 5.0 and 5.5.
Standard stock solution— Transfer 221 mg of sodium fluoride, previously dried at 150 for 4 hours, to a 100-mL volumetric flask, add about 20 mL of water, and mix to dissolve. Add 1.0 mL of sodium hydroxide solution (1 in 2500), dilute with water to volume, and mix. Each mL of this solution contains 1 mg of fluoride ions. Store in a tightly closed, plastic container.
Standard solutions— Dilute portions of the Standard stock solution quantitatively and stepwise with pH 5.25 buffer to obtain 100-mL solutions having concentrations of 1, 3, 5, and 10 µg per mL.
Test solution— Shake 25 mL with 25 mL of water for 5 minutes, and allow the liquids to separate completely. Transfer 5.0 mL of the water layer to a 10-mL volumetric flask, dilute with pH 5.25 buffer to volume, and mix.
Procedure— Concomitantly measure the potential (see Titrimetry 541), in mV, of the Standard solutions and the Test solution, with a pH meter capable of a minimum reproducibility of ±0.2 mV, equipped with a glass-sleeved calomel-fluoride specific-ion electrode system. [note—When taking measurements, immerse the electrodes in the solution which has been transferred to a 150-mL beaker containing a polytef-coated stirring bar. Allow to stir on a magnetic stirrer having an insulated top until equilibrium is attained (1 to 2 minutes), and record the potential. Rinse and dry the electrodes between measurements, taking care to avoid damaging the crystal of the specific-ion electrode. ] Plot the logarithm of the fluoride-ion concentrations, in µg per mL, of the Standard solutions versus potential, in mV. From the measured potential of the Test solution and the standard curve, determine the concentration, in µg per mL, of fluoride ions in the Test solution: not more than 10 µg per mL is found.
Assay— Inject a volume of Enflurane of suitable size, but not more than 30 µL, into a suitable gas chromatograph (see Gas Chromatography under Chromatography 621) equipped with a thermal conductivity detector. Under typical conditions, the instrument contains a 4-mm × 3-m stainless steel column packed with 20% liquid phase G4 on 60- to 80-mesh S1A, the column is temperature-programmed at about 6 per minute from 60 to 125, and the injection port temperature is maintained at about 200. Dry helium is used as the carrier gas at a flow rate of about 60 mL per minute. Calculate the percentage purity by dividing 100 times the area under the Enflurane peak by the sum of all of the areas in the chromatogram.
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Topic/Question Contact Expert Committee
Monograph Domenick Vicchio, Ph.D.
Senior Scientific Liaison
(SM42010) Monographs - Small Molecules 4
Reference Standards RS Technical Services
USP35–NF30 Page 3038