Isobutane
If you find any inaccurate information, please let us know by providing your feedback here
This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
C₄H₁₀ 58.12
1 DEFINITION
Isobutane contains NLT 95.0% of isobutane (C₄H₁₀).
[Caution-Isobutane is highly flammable and explosive.]
2 IDENTIFICATION
A. IR Absorption: Exhibits maxima, among others, at about the following wavelengths (µm): 3.4 (vs), 6.8 (s), 7.2 (m), 8.5 (m), and 10.9 (m).
B. The vapor pressure of a test specimen obtained as directed for Propellants 〈602〉, and determined at 21° by means of a suitable pressure gauge, is between 303 and 331 kPa absolute (44 and 48 psia).
3 ASSAY
3.1 Procedure
Chromatographic system
- (See Chromatography 〈621〉, System Suitability.)
- Mode: GC
- Detector: Thermal conductivity
- Column: 3-mm × 6-m aluminum; packed with 10 weight percent of liquid phase G30 on support S1D
- Column temperature: 33°
- Carrier gas: Helium
- Flow rate: 50 mL/min
- Injection volume: 2 µL
System suitability
- Sample: Isobutane
- Suitability requirements
- Sample response comparison: Peak responses for isobutane from duplicate injections agree within 1%.
Analysis
Sample: Isobutane
Connect one Isobutane cylinder to the chromatograph through a suitable sampling valve and a flow control valve downstream from the sampling valve. Flush the liquid specimen through the sampling valve, taking care to avoid entrapment of gas or air in the sampling valve.
Calculate the percentage purity of Isobutane:
Result = (rU/rT) × 100
rU = peak response of isobutane
rT = sum of all the peak responses
Acceptance criteria: NLT 95.0%
4 SPECIFIC TESTS
Water: NMT 0.001%, determined as directed in Propellants 〈602〉
High-Boiling Residues: NMT 5 µg/mL, determined as directed in Propellants 〈602〉
Acidity of Residue
- Sample: Residue from the test for High-Boiling Residues
- Analysis: Add 10 mL of water to the Sample, mix by swirling for about 30 s, add 2 drops of methyl orange TS, insert the stopper in the tube, and shake vigorously.
- Acceptance criteria: No pink or red color appears in the aqueous layer.
5 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in tight cylinders, and prevent exposure to excessive heat.
