Methyl Alcohol

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

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

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CH₄OH 32.04

Methanol CAS RN^®: 67-56-1.

1 DEFINITION

Methyl Alcohol contains NLT 99.5% of CH₃OH.

[Caution-Methyl Alcohol is poisonous.]

2 IDENTIFICATION

Change to read:

A. SPECTROSCOPIC IDENTIFICATION TESTS 〈197〉, Infrared Spectroscopy: 197F (CN 1-May-2020)

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

3.1 PROCEDURE

System suitability solution: Dilute 1.0 mL of USP Methyl Alcohol RS and 1.0 mL of USP Acetone RS with tetrahydrofuran to 50 mL.

Internal standard solution: 2% (v/v) acetonitrile in tetrahydrofuran

Standard solution: 15.8 mg/mL of USP Methyl Alcohol RS in Internal standard solution

Sample solution: 15.8 mg/mL of Methyl Alcohol in Internal standard solution

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Detector: Flame ionization

Column: 0.32-mm × 30-m fused-silica capillary column, coated with a 1.8-µm layer of phase G43

Temperature

Injector: 200°

Detector: 280°

Column: See Table 1.

Table 1

Carrier gas: Helium

Linear velocity: 35 cm/s

Injection type: Split ratio, 20:1

Injection size: 1 µL

System suitability

Samples: System suitability solution and Standard solution

[Note-The relative retention times for methyl alcohol, acetone, and acetonitrile are 1.0, about 1.6, and about 1.8, respectively.]

Suitability requirements

Resolution: NLT 15 between methyl alcohol and acetone, System suitability solution

Tailing factor: NMT 1.5 for methyl alcohol, System suitability solution

Relative standard deviation: NMT 2.0% for the ratio of the peak area of methyl alcohol to acetonitrile, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of methyl alcohol (CH₃OH) in the portion of Methyl Alcohol taken:

Result = (R_U/R_S) × (C_S/C_U) × 100

R_U = peak area ratio from the Sample solution

R_S = peak area ratio from the Standard solution

C_S = concentration of USP Methyl Alcohol RS in the Standard solution (mg/mL)

C_U = concentration of Methyl Alcohol in the Sample solution (mg/mL)

Acceptance criteria: NLT 99.5%

4 IMPURITIES

4.1 NONVOLATILE RESIDUE

Sample: 250 mL of Methyl Alcohol

Analysis: Evaporate the Sample in a 600-mL beaker on a steam bath, in a well-ventilated hood, until the volume is reduced to about 100 mL. Cool, transfer a portion of the liquid to a suitable, tared 50-mL platinum dish on a steam bath, and evaporate. Repeat the process until all of the liquid has been transferred, and then evaporate to dryness. Dry at 105° for 30 min, cool, and weigh.

Acceptance criteria: The weight of the residue does not exceed 2 mg, corresponding to NMT 0.001% (w/w).

4.2 ACETONE AND ALDEHYDES (as acetone)

Standard solution: Dilute 1.9 mL (1.5 g) of acetone with water to 1000 mL, then dilute 1.0 mL of this solution with water to 100 mL. Dilute 2 mL of the resulting solution with water to 5 mL. The Standard solution contains 30 µg of acetone and is freshly prepared.

Sample solution: Dilute 1.25 mL (1 g) of Methyl Alcohol with water to 5 mL.

Analysis: Adjust to and maintain each solution at 20°. Add 5 mL of alkaline mercuric–potassium iodide TS to each of the Standard solution and Sample solution.

Acceptance criteria: Any turbidity produced in the Sample solution is not greater than that produced in the Standard solution (NMT 0.003%).

4.3 READILY CARBONIZABLE SUBSTANCES 〈271〉

Sample: 5 mL

Analysis: Cool 5 mL of sulfuric acid, contained in a small conical flask, to 10°, and add the Sample dropwise with constant mixing, maintaining the temperature below 20° throughout the test.

Acceptance criteria: No discoloration develops.

4.4 READILY OXIDIZABLE SUBSTANCES

Sample: 20 mL of Methyl Alcohol

Analysis: Cool the Sample to 15°, add 0.1 mL of 0.1 N potassium permanganate, and allow to stand at 15°.

Acceptance criteria: The pink color does not completely disappear within 5 min.

5 SPECIFIC TESTS

5.1 ACIDITY

Sample solution: Mix 25 mL of water with 10 mL of alcohol and 0.5 mL of phenolphthalein TS, and add 0.02 N sodium hydroxide until a slight pink color persists after shaking for 30 s. Taking precautions to avoid absorption of carbon dioxide, add 19 mL (15 g) of Methyl Alcohol.

Analysis: Titrate the Sample solution with 0.020 N sodium hydroxide.

Acceptance criteria: NMT 0.45 mL of 0.020 N sodium hydroxide is required to produce a pink color.

5.2 ALKALINITY (as ammonia)

Sample: 28.6 mL (22.6 g) of Methyl Alcohol

Analysis: Mix the Sample with 25 mL of water, add 1 drop of methyl red TS, and titrate with 0.020 N sulfuric acid.

Acceptance criteria: NMT 0.20 mL of 0.020 N sulfuric acid is required to produce a pink color (3 ppm).

5.3 WATER DETERMINATION, Method I 〈921〉: NMT 0.1%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers, remote from heat, sparks, and open flames.

USP REFERENCE STANDARDS 〈11〉

USP Acetone RS

USP Methyl Alcohol RS