(eye'' soe bue' tane).
» Isobutane contains not less than 95.0 percent of isobutane (C4H10).
[CautionIsobutane is highly flammable and explosive. ]
Packaging and storage Preserve in tight cylinders, and prevent exposure to excessive heat.
A: The IR absorption spectrum of it exhibits maxima, among others, at about the following wavelengths, in 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 in the General Sampling Procedure under Propellants (see Aerosols, Nasal Sprays, Metered-Dose Inhalers, and Dry Powder Inhalers 601), determined at 21 by means of a suitable pressure gauge, is between 303 and 331 kPa absolute (44 and 48 psia).
Water: not more than 0.001%, determined as directed for Water Content under Aerosols, Nasal Sprays, Metered-Dose Inhalers, and Dry Powder Inhalers 601.
High-boiling residues: not more than 5 µg per mL, determined as directed for High-Boiling Residues, Method II, under Aerosols, Nasal Sprays, Metered-Dose Inhalers, and Dry Powder Inhalers 601.
Acidity of residue Add 10 mL of water to the residue obtained in the test for High-boiling residues, mix by swirling for about 30 seconds, add 2 drops of methyl orange TS, insert the stopper in the tube, and shake vigorously: no pink or red color appears in the aqueous layer.
Chromatographic system Under typical conditions, the gas chromatograph is equipped with a thermal-conductivity detector and contains a 3-mm × 6-m aluminum column packed with 10 weight percent of liquid phase G30 on non-acid-washed support S1C, helium is used as the carrier gas at a flow rate of 50 mL per minute, and the temperature of the column is maintained at 33.
System suitability The peak responses obtained for Isobutane in the chromatograms from duplicate determinations agree within 1%.
Procedure Connect 1 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. Inject a suitable volume, typically 2 µL, of Isobutane into the chromatograph, and record the chromatogram. Calculate the percentage purity by dividing 100 times the Isobutane response by the sum of all of the responses in the chromatogram.