Dehydrated Alcohol

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

DOWNLOAD PDF HERE

C₂H₆O 46.07

Ethanol;

Ethyl alcohol CAS RN®: 64-17-5.

1 DEFINITION

Dehydrated Alcohol contains NLT 99.2% by weight, corresponding to NLT 99.5% by volume, at 15.56°, of Ethanol (C₂H₅OH).

2 IDENTIFICATION

A. It meets the requirements of the test for Specific Gravity 〈841〉.

B. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F or 197S: Neat

C. Limit of Methanol

[Note-This test must be performed to be in compliance with USP, in addition to Identification A and B above.]

Sample solution A, Standard solution A, Standard solution B, Standard solution C, Chromatographic system, and System suitability: Proceed as directed in Organic Impurities.

Analysis: Proceed as directed in the Organic Impurities test, Methanol calculation.

Acceptance criteria: Meets the requirements in Table 2 for methanol.

3 IMPURITIES

3.1 Limit of Nonvolatile Residue

Sample: 100 mL of Dehydrated Alcohol

Analysis: Evaporate the Sample in a tared dish on a water bath, and dry at 100°–105° for 1 h.

Acceptance criteria: The weight of the residue is NMT 2.5 mg.

3.2 Organic Impurities

Sample solution A: Dehydrated Alcohol (substance under test)

Sample solution B: 300 µL/L of 4-methylpentan-2-ol in Sample solution A

Standard solution A: 200 µL/L of methanol in Sample solution A

• [Note-To be prepared for use in Identification C.]

Standard solution B: 10 µL/L each of methanol and acetaldehyde in Sample solution A

Standard solution C: 30 µL/L of acetal in Sample solution A

Standard solution D: 2 µL/L of benzene in Sample solution A

Chromatographic system

• (See Chromatography 〈621〉, System Suitability.)
• Mode: GC
• Detector: Flame ionization
• Column: 0.32-mm × 30-m fused-silica capillary; bonded with a 1.8-µm layer of phase G43
• Injection type: Split; split ratio 20:1
• Temperatures
• Injection port: 200°
• Detector: 280°
• Column: See Table 1.

• Flow rate: 35 cm/s
• Carrier gas: Helium
• Injection volume: 1.0 µL

System suitability

• Sample: Standard solution B
• Suitability requirements
• Resolution: NLT 1.5 between the first major peak (acetaldehyde) and the second major peak (methanol)

Analysis

Samples: Sample solution A, Sample solution B, Standard solution A, Standard solution B, Standard solution C, and Standard solution D

Methanol calculation

[Note-To be performed as a part of Identification C.]

Result = r_u/r_s

r_u = peak area of methanol from Sample solution A

r_s = peak area of methanol from Standard solution A

Acetaldehyde calculation (sum of acetaldehyde and acetal)

Result = {[A_E/(A_T − A_E)] × C_A} + {[D_E/(D_T − D_E)] × C_D × (M_r1/M_r2)}

A_E = peak area of acetaldehyde from Sample solution A

A_T = peak area of acetaldehyde from Standard solution B

C_A = concentration of acetaldehyde in Standard solution B (µL/L)

D_E = peak area of acetal from Sample solution A

D_T = peak area of acetal from Standard solution C

C_D = concentration of acetal in Standard solution C (µL/L)

M_r1 = molecular weight of acetaldehyde, 44.05

M_r2 = molecular weight of acetal, 118.2

Benzene calculation

Result = [B_E/(B_T − B_E)] × C_B

B_E = peak area of benzene from Sample solution A

B_T = peak area of benzene from Standard solution D

C_B = concentration of benzene in Standard solution D (µL/L)

[Note-If necessary, the identity of benzene can be confirmed using another suitable chromatographic system (stationary phase with a different polarity).]

Any other impurity calculation

Result = (r_U/r_M) × C_M

r_U = peak area of each impurity from Sample solution B

r_M = peak area of 4-methylpentan-2-ol from Sample solution B

C_M = concentration of 4-methylpentan-2-ol in Sample solution B (µL/L)

Acceptance criteria: See Table 2.

ᵃ Disregard any peaks of less than 9 µL/L (0.03 times the area of the peak corresponding to 4-methylpentan-2-ol in Sample solution B).

4 SPECIFIC TESTS

Change to read:

4.1 Specific Gravity 〈841〉

NMT 0.7962 at 15.56°, indicating NLT 99.2% of ethanol (C₂H₅OH) by weight

[Note-In the event that a temperature of 15.56° cannot be reached, the Alcoholometric Table found in the Reagents and Reference Tables section of USP-NF can be used to provide the conversion factors needed to complete this test at other temperatures.]

4.2 Ultraviolet Absorption

Analytical wavelength: 235-340 nm

Cell: 5 cm

Reference: Water

Acceptance criteria

• Absorbance: NMT 0.40 at 240 nm; NMT 0.30 between 250 and 260 nm; NMT 0.10 between 270 and 340 nm
• Curve: The spectrum shows a steadily descending curve with no observable peaks or shoulders.

4.3 Clarity of Solution

[Note-Compare each Sample solution to Standard suspension A and to water in diffused daylight 5 min after preparation of Standard suspension A.]

Hydrazine solution: 10 mg/mL of hydrazine sulfate in water. Allow to stand for 4–6 h.

Methenamine solution: Transfer 2.5 g of methenamine to a 100-mL glass-stoppered flask, add 25.0 mL of water, insert the stopper, and mix to dissolve.

Primary opalescence suspension: Transfer 25.0 mL of Hydrazine solution to the Methenamine solution. Mix, and allow to stand for 24 h. 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.

Opalescence standard: Transfer 15.0 mL of the Primary opalescence suspension to a 1000-mL volumetric flask, and dilute with water to volume. This suspension should not be used beyond 24 h after preparation.

Standard suspension A: Dilute 5.0 mL of the Opalescence standard with water to 100.0 mL.

Standard suspension B: Dilute 10.0 mL of the Opalescence standard with water to 100.0 mL.

Sample solution A: Substance under test

Sample solution B: 1.0 mL of Sample solution A diluted with water to 20 mL. Allow to stand for 5 min before testing.

Blank: Water

Analysis

Samples: Standard suspension A, Standard suspension B, Sample solution A, Sample solution B, and Blank

Transter a sufficient portion of Sample solution A and Sample solution B to separate test tubes of colorless, transparent, neutral glass with a flat base and an internal diameter of 15-25 mm to obtain a depth of 40 mm. Similarly transfer portions of Standard suspension A, Standard suspension B, and Blank to separate matching test tubes. Compare the Samples in diffused daylight, viewing vertically against a black background (see Visual Comparison (630)). The diffusion of light must be such that Standard suspension A can be readily distinguished from water, and Standard suspension B can be readily distinguished from Standard suspension A.

Acceptance criteria: Sample solution A and Sample solution B show the same clarity as that of water, or their opalescence is not more pronounced than that of Standard suspension A.

4.4 Acidity or Alkalinity

Phenolphthalein solution: Dissolve 0.1 g of phenolphthalein in 80 mL of alcohol, and dilute with water to 100 mL.

Sample: 20 mL of Dehydrated Alcohol

Analysis: 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.

Acceptance criteria: The solution is pink (30 µg/g, expressed as acetic acid).

4.5 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 mg/mL).

Standard solution: 1.0 mL of Standard stock solution, diluted with dilute hydrochloric acid (10 mg/mL) to 100 mL. Prepare the Standard solution immediately before use.

Sample solution: Substance under test

Blank: Water

Analysis

Samples: Standard solution, Sample solution, and Blank

Transfer a sufficient portion of each of the Samples to individual test tubes of colorless, transparent, neutral glass with a flat base and an internal diameter of 15-25 mm to obtain a depth of 40 mm. Compare the Samples in diffused daylight, viewing vertically against a white background (see Visual Comparison (630)).

Acceptance criteria: The Sample solution has the appearance of water or is not more intensely colored than the Standard solution.,

5 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers, protected from light.

USP REFERENCE STANDARDS (11)

USP Dehydrated Alcohol RS