Dehydrated Alcohol
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C2H6O 46.07

Ethanol.
Ethyl alcohol [64-17-5].
» Dehydrated Alcohol contains not less than 99.2 percent, by weight, corresponding to not less than 99.5 percent, by volume, at 15.56, of C2H5OH.
Packaging and storage— Preserve in tight containers, protected from light.
USP Reference standards 11
USP Dehydrated Alcohol RS Click to View Structure
Clarity of solution— [note—The Test solution is to be compared to Reference suspension A and to water in diffused daylight 5 minutes after preparation of Reference suspension A. ]
Hydrazine solution— Transfer 1.0 g of hydrazine sulfate to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix. Allow to stand for 4 to 6 hours.
Methenamine solution— Transfer 2.5 g of methenamine to a 100-mL glass-stoppered flask, add 25.0 mL of water, insert the glass stopper, and mix to dissolve.
Primary opalescent suspension— [note—This suspension is stable for 2 months, provided it is stored in a glass container free from surface defects. The suspension must not adhere to the glass and must be well mixed before use. ] Transfer 25.0 mL of Hydrazine solution to the Methenamine solution in the 100-mL glass-stoppered flask. Mix, and allow to stand for 24 hours.
Opalescence standard— [note—This suspension should not be used beyond 24 hours after preparation. ] Transfer 15.0 mL of the Primary opalescent suspension to a 1000-mL volumetric flask, dilute with water to volume, and mix.
Reference suspensions— Transfer 5.0 mL of the Opalescence standard to a 100-mL volumetric flask, dilute with water to volume, and mix to obtain Reference suspension A. Transfer 10.0 mL of the Opalescence standard to a second 100-mL volumetric flask, dilute with water to volume, and mix to obtain Reference suspension B.
Test solution A: substance to be examined.
Test solution B— Dilute 1.0 mL of Test solution A with water to 20 mL, and allow to stand for 5 minutes before testing.
Procedure— Transfer a sufficient portion of Test solution A and Test solution B to separate test tubes of colorless, transparent, neutral glass with a flat base and an internal diameter of 15 to 25 mm to obtain a depth of 40 mm. Similarly transfer portions of Reference suspension A, Reference suspension B, and water to separate, matching test tubes. Compare Test solution A, Test solution B, Reference suspension A, Reference suspension B, and water in diffused daylight, viewing vertically against a black background (see Visual Comparison under Spectrophotometry and Light-Scattering 851). [note—The diffusion of light must be such that Reference suspension A can readily be distinguished from water, and Reference suspension B can readily be distinguished from Reference suspension A. ] Test solution A and Test solution B show the same clarity as that of water, or their opalescence is not more pronounced than that of Reference suspension A.
Color of solution—
Standard stock solution— Combine 3.0 mL of ferric chloride CS, 3.0 mL of cobaltous chloride CS, 2.4 mL of cupric sulfate CS, and 1.6 mL of dilute hydrochloric acid (10 g per L).
Standard solution— [note—Prepare the Standard solution immediately before use. ] Transfer 1.0 mL of Standard stock solution to a 100-mL volumetric flask, dilute with dilute hydrochloric acid (10 g per L) to volume, and mix.
Test solution: substance to be examined.
Procedure— Transfer a sufficient portion of the Test solution to a test tube of colorless, transparent, neutral glass with a flat base and an internal diameter of 15 to 25 mm to obtain a depth of 40 mm. Similarly transfer portions of Standard solution and water to separate matching test tubes. Compare the Test solution, Standard solution, and water in diffused daylight, viewing vertically against a white background (see Visual Comparison under Spectrophotometry and Light-Scattering 851). The Test solution has the appearance of water or is not more intensely colored than the Standard solution.
Identification—
A: It complies with the test for Specific gravity.
Specific gravity 841: not more than 0.7962 at 15.56, indicating not less than 99.2% of C2H5OH, by weight.
Acidity or alkalinity—
Phenolphthalein solution— Dissolve 0.1 g of phenolphthalein in 80 mL of alcohol, and dilute with water to 100 mL.
Procedure— To 20 mL of alcohol, add 20 mL of freshly boiled and cooled water and 0.1 mL of Phenolphthalein solution. The solution is colorless. Add 1.0 mL of 0.01 N sodium hydroxide. The solution is pink (30 ppm, expressed as acetic acid).
Ultraviolet absorption— Record the UV absorption spectrum of the test material from 200 to 400 nm in a 5-cm cell: maximum absorbance 0.40 at 240 nm, 0.30 between 250 and 260 nm, and 0.10 between 270 and 340 nm. Examine between 235 and 340 nm, in a 5-cm cell, using water as the compensation liquid. The absorption curve is smooth.
Volatile impurities—
Test solution A: substance to be examined.
Test solution B— Add 150 µL of 4-methylpentan-2-ol to 500.0 mL of the substance to be examined.
Standard solution A— Dilute 100 µL of methanol with the substance to be examined to 50.0 mL. Dilute 5.0 mL of the solution with the substance to be examined to 50.0 mL.
Standard solution B— Dilute 50 µL of methanol and 50 µL of acetaldehyde with the substance to be examined to 50.0 mL. Dilute 100 µL of the solution with the substance to be examined to 10.0 mL.
Standard solution C— Dilute 150 µL of acetal with the substance to be examined to 50.0 mL. Dilute 100 µL of the solution with the substance to be examined to 10.0 mL.
Standard solution D— Dilute 100 µL of benzene with the substance to be examined to 100.0 mL. Dilute 100 µL of the solution with the substance to be examined to 50.0 mL.
Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector, maintained at about 280, and a 0.32-mm × 30-m fused silica capillary column bonded with a 1.8-µm layer of phase G43. The carrier gas is helium with a linear velocity of about 35 cm per second and a split ratio of 1:20. The column temperature is maintained at 40 for the first 12 minutes after an injection is made and is increased from 40 to 240 from 12 to 32 minutes after injection. During the period of 32 to 42 minutes after an injection is made the column temperature is maintained at 240. The injection port temperature is maintained at 200. Chromatograph Standard solution B, and record the peak responses as directed for Procedure: the resolution, R, between the first major peak (acetaldehyde) and the second major peak (methanol) is not less than 1.5.
Procedure— Separately inject equal volumes (1.0 µL) of Test solution A, Test solution B, Standard solution A, Standard solution C, and Standard solution D into the chromatograph, record the chromatograms, and measure the major peaks. Calculate the concentration of methanol in Test solution A: not more than half the area of the corresponding peak in the chromatogram obtained with Standard solution A (200 ppm).
Calculate the sum of the contents of acetaldehyde and acetal, expressed as acetaldehyde, using the following formula:
[(10 × AE)/(ATAE)] + [(30 × CE)/(CT – CE)]
in which AE is the area of the acetaldehyde peak in the chromatogram obtained with Test solution A; AT is the area of the acetaldehyde peak in the chromatogram obtained with Standard solution B; CE is the area of the acetal peak in the chromatogram obtained with Test solution A; and CT is the area of the acetal peak in the chromatogram obtained with Standard solution C: not more than 10 ppm, expressed as acetaldehyde is found.
Calculate the content of benzene using the following formula:
(2BE)/(BTBE)
in which BE is the area of the benzene peak in the chromatogram obtained with Test solution A, and BT is the area of the benzene peak in the chromatogram obtained with Standard solution D: not more than 2 ppm is found. If necessary, the identity of benzene can be confirmed using another suitable chromatographic system (stationary phase with a different polarity).
The total of all other impurities in the chromatogram obtained with Test solution B is not more than the area of the peak due to 4-methylpentan-2-ol in the chromatogram obtained with Test solution B (300 ppm). Disregard any peaks that are 0.03 times the area of the peak corresponding to 4-methylpentan-2-ol in the chromatogram obtained with Test solution B (9 ppm).
Limit of nonvolatile residue— Evaporate 100 mL in a tared dish on a water bath, and dry at 100 to 105 for 1 hour: the weight of the residue does not exceed 2.5 mg.
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