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).

(Official January 1, 2007)

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.