Isobutyl 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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CH₃CH(CH₃)CH₂OH 74.12

2-Methyl-1-propanol;

2-Methylpropyl alcohol;

1-Isobutanol CAS RN: 78-83-1.

1 DEFINITION

Isobutyl Alcohol contains NLT 98.0% of 2-methyl-1-propanol (C₄H₁₀O).

2 IDENTIFICATION

A. SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197F

B. The retention time of the major peak of the Sample solution corresponds to that of the 2-methyl-1-propanol peak of the System suitability solution, as obtained in the Assay.

3 ASSAY

Change to read:

PROCEDURE

System suitability solution: USP 1-Butanol RS and USP 2-Methyl-1 -Propanol RS (1:1)

Reference solution: 0.1% of Isobutyl Alcohol in water

Sample solution: Isobutyl Alcohol (neat)

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.53 - mm * 30 - m coated with a 3.0-um layer of thickness phase G43

Temperatures

Detector: 250°

Injection port: 140°

Column: See Table 1.

Table 1
 

Carrier gas: Helium

Flow rate: 4.8–4.9 mL/min

Injection volume: 1 µL

Injection type: Split injection. The split ratio is 30:1. [Note—A needle wash with the Sample solution is recommended to minimize the carry over.]

System suitability

Sample: System suitability solution

[Note—The 2-methyl-1-propanol peak typically elutes at about 11 min, and 1-butanol at about 15 min. The relative retention times for 2-methyl-1-propanol and 1-butanol are 0.7 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 2.0 between 2-methyl-1-propanol and 1-butanol

Relative standard deviation: NMT 2.0%

Analysis

Samples: Reference solution and Sample solution

Calculate the percentage of 2-methyl-1-propanol (C₄H₁₀O) in the portion of Isobutyl Alcohol taken:

Result = (r_U /r_T ) × 100

r_U = peak response of isobutyl alcohol

r_{T(ERR 1-Feb2023)}= sum of all the peaks except those each of which with an area less than 0.1 times the area of the major peak from the Reference solution

Acceptance criteria: NLT 98.0%

4 IMPURITIES

LIMIT OF ISOBUTYRALDEHYDE, BUTYRALDEHYDE, 2-BUTANOL, 1-BUTANOL, AND OTHER VOLATILE IMPURITIES

Sample solution and Chromatographic system: Proceed as directed in the Assay.

Reference solution: 0.1% of Isobutyl Alcohol in water

Standard solution: 0.2% of USP Isobutyraldehyde RS, 0.2% of USP Butyraldehyde RS, 0.1% of USP 1-Butanol RS, and 0.1% of USP 2-Butanol RS

in the Sample solution

System suitability

Sample: Standard solution

[NOTE-See Table 2 for relative retention times.]

Table 2

Suitability requirements

Resolution: NLT 1.5 between all adjacent peaks

Analysis

Samples: Sample solution, Reference solution, and Standard solution

If any peaks of the Sample solution have the same retention times as the peaks due to isobutyraldehyde, butyraldehyde, 2-butanol, and 1- butanol, subtract the areas of any such peaks from the peak areas of the Standard solution at these retention times. The difference is calculated below:

Result (Δr) = r_s − r_u

r_s = peak response of each individual impurity (isobutyraldehyde, butyraldehyde, 2-butanol, or 1-butanol) from the Standard solution

r_u = peak response of each individual impurity (isobutyraldehyde, butyraldehyde, 2-butanol, or 1-butanol), if present, from the Sample solution

Calculate the percentage of each impurity other than isobutyraldehyde, butyraldehyde, 2-butanol, and 1-butanol in the portion of Isobutyl Alcohol taken:

Result = (r_u /r_T ) × 100

r_u = peak response of each impurity other than isobutyraldehyde, butyraldehyde, 2-butanol, and 1-butanol from the Sample solution

r_T = sum of all the peaks from the Sample solution, except those each of which with an area less than 0.1 times the area of the major peak from the Reference solution)

Acceptance criteria: See Table 3. Disregard any peak with an area less than 0.1 times the area of the major peak from the Reference solution, corresponding to 0.01%.

Table 3

LIMIT OF NONVOLATILE RESIDUE

Sample: 100 mL

Analysis: Evaporate the Sample in a tared porcelain dish on a steam bath, and dry at 105° for 30 min.

Acceptance criteria: The weight of the residue does not exceed 4 mg, corresponding to NMT 0.004%.

5 SPECIFIC TESTS

ACIDITY

Sample: 74 mL (60 g)

Analysis: Titrate the Sample with 0.020 N alcoholic potassium hydroxide, using phenolphthalein TS as the indicator, until a pink color persists for NLT 15 s.

Acceptance criteria: NMT 2.5 mL is consumed.

WATER DETERMINATION, Method/(921): NMT 0.5%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers, and prevent exposure to excessive heat.

USP REFERENCE STANDARDS (11)

USP 1-Butanol RS

USP 2-Butanol RS

USP Butyraldehyde RS

USP Isobutyraldehyde RS

USP 2-Methyl-1-Propanol RS