Isopropyl 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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C₃H₈O 60.10 

2-Propanol; 

Isopropanol CAS RN®: 67-63-0. 

1 DEFINITION 

Isopropyl Alcohol contains NLT 99.0% of isopropyl alcohol (C₃H₈O). 

2 IDENTIFICATION 

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197F 

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

C. Limit of Methanol 

[Note—This test must be performed to be in compliance with USP, in addition to Identification A and B above.] System suitability solution, Sample, Standard solution A, Chromatographic system, and System suitability: Proceed as directed in the Assay and Limit of Volatile Impurities test. 

Analysis: Proceed as directed in the Limit of Volatile Impurities test, Methanol calculation. 

Acceptance criteria: Meets the requirements in Table 3 for methanol 

3 ASSAY 

Change to read: 

Procedure 

System suitability solution: Transfer 1 µL of methanol and 5 µL of ethyl acetate into a 5-mL volumetric flask, and dilute to volume with USP 2-Propanol System Suitability RS to have  200 µL/L of methanol and 1000 µL/L of ethyl acetate in USP 2-Propanol System Suitability RS. 

Sample: Isopropyl Alcohol (substance under test) 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: GC 

Detector: Flame ionization 

Column: 0.25-mm × 60-m fused silica column, coated with a 1.4-µm lm of phase G43 

Temperatures 

Detector: 200° 

Injection port: 150° 

Column: See Table 1. 

Table 1 

Carrier gas: Helium 

Flow rate: 2.3 mL/min 

Injection volume: 1 µL 

Injection type: Split, split ratio 50:1. [Note—A 4-mm straight liner is suitable.] 

Run time: 26 min 

System suitability 

Sample: System suitability solution 

[Note—See Table 2.] 

Table 2 

^a Ethyl acetate   is not a known impurity. It is used for calculation of unspecified impurities only. 

Suitability requirements 

Resolution: NLT 1.5 between acetone and isopropyl alcohol 

Tailing factor: NMT 2.0 for the isopropyl alcohol peak 

Relative standard deviation: NMT 2.0% for the isopropyl alcohol peak of 6 replicate injections, System suitability solution Signal-to-noise ratio: NLT 10 for any of the following peaks: methanol, ethyl ether, acetone,   diisopropyl ether, 1- propanol, 2-butanol, and ethyl acetate 

Analysis 

Sample: Sample 

Calculate the percentage of isopropyl alcohol (C₃H₈O) in the portion of Isopropyl Alcohol taken: 

Result = (r_U/r_T) × 100 

r_U = peak response of isopropyl alcohol from the Sample 

r_T = sum of all the peak responses from the Sample 

Acceptance criteria: NLT 99.0% 

4 IMPURITIES 

Limit of Volatile Impurities 

System suitability solution, Sample, Chromatographic system, and System suitability: Proceed as directed in the Assay. Standard solution A: 200 µL/L of methanol in the Sample 

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

Standard solution B: 1000 µL/L each of acetone, diisopropyl ether, ethyl ether, 1-propanol, 2-butanol, and ethyl acetate in the Sample Analysis 

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

Methanol calculation: 

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

Result (% v/v) = {[M_U/(M_S− M_U)] × C_M}/10,000 

M_U = peak area of methanol from the Sample 

M_S = peak area of methanol from Standard solution A 

C_M = concentration of spiked methanol from Standard solution A (µL/L) 

Individual known impurity (ethyl ether, acetone, diisopropyl ether, 1-propanol, 2-butanol) calculation: 

Result (% v/v) = {[K_U/(K_S − K_U)] × C_K}/10,000 

K_U = peak area of individual known impurity from the Sample 

K_S = peak area of individual known impurity from Standard solution B 

C_K = concentration of spiked individual known impurity from Standard solution B (µL/L) 

Individual unspecified impurity calculation: 

Result (% v/v) = [(r_U/r_S) × C_S]/10,000 

r_U = peak area of each unspecified impurity from the Sample 

r_S = peak area of ethyl acetate from Standard solution B 

C_S = concentration of ethyl acetate from Standard solution B (μL/L) 

Acceptance criteria: See Table 3. 

Table 3 

^a To be performed as a part of Identification C. 

Limit of Nonvolatile Residue 

Sample: 50 mL 

Analysis: Evaporate the Sample in a tared porcelain dish on a steam bath to dryness, and heat at 105° for 1 h. 

Acceptance criteria: NMT 2.5 mg (0.005%) 

5 SPECIFIC TESTS 

Specific Gravity 〈841〉: 0.783–0.787 

Refractive Index 〈831〉: 1.376–1.378 at 20° 

Acidity 

Sample solution: To 50 mL of Isopropyl Alcohol add 100 mL of carbon dioxide-free water. 

Analysis: To the Sample solution add 2 drops of phenolphthalein TS, and titrate with 0.020 N sodium hydroxide to a pink color that persists for 30 s. 

Acceptance criteria: NMT 0.70 mL of 0.020 N sodium hydroxide is required for neutralization. 

Water Determination 〈921〉, Method I 

Sample: 5.0 g 

Acceptance criteria: NMT 0.5% 

Add the following: 

Ultraviolet Absorption 

Sample: Isopropyl Alcohol 

Analytical wavelength: 230–310 nm 

Cell: 1 cm 

Reference: Water 

Acceptance criteria 

Absorbance: NMT 0.30 at 230 nm; NMT 0.10 at 250 nm; NMT 0.03 at 270 nm; NMT 0.02 at 290 nm; NMT 0.01 at 310 nm Curve: The spectrum shows a steadily descending curve with no observable peaks or shoulders.  

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers, and prevent exposure to excessive heat. Protect from light. 

USP Reference Standards 〈11〉 

USP 2-Propanol RS 

USP 2-Propanol System Suitability RS 

It contains isopropyl alcohol with 0.1% each of ethyl ether, acetone, diisopropyl ether, 1-propanol, and 2-butanol.