Isobutane
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»Isobutane contains not less than 95.0percent of isobutane (C4H10).
Packaging and storage—
Preserve in tight cylinders,and prevent exposure to excessive heat.
Identification—
A:
The IRabsorption 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 Procedureunder Propellants (see Aerosols,Nasal Sprays,Metered-Dose Inhalers,and Dry Powder Inhalers á601ñ),determined at 21
by means of a suitable pressure gauge,is between 303and 331kPa absolute (44and 48psia).
by means of a suitable pressure gauge,is between 303and 331kPa absolute (44and 48psia).
Water:
not more than 0.001%,determined as directed for Water Content under Aerosols,Nasal Sprays,Metered-Dose Inhalers,and Dry Powder Inhalers á601ñ.
High-boiling residues:
not more than 5µg per mL,determined as directed for High-Boiling Residues,Method II,under Aerosols,Nasal Sprays,Metered-Dose Inhalers,and Dry Powder Inhalers á601ñ.
Acidity of residue—
Add 10mLof water to the residue obtained in the test for High-boiling residues,mix by swirling for about 30seconds,add 2drops of methyl orange TS,insert the stopper in the tube,and shake vigorously:no pink or red color appears in the aqueous layer.
Limit of sulfur compounds—
Carefully open the container valve to produce a moderate flow of gas.Do not direct the gas stream toward the face,but deflect a portion of the stream toward the nose:the odor is free from the characteristic odor of sulfur compounds.
Assay—
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 10weight percent of liquid phase G30on non-acid-washed support S1C,helium is used as the carrier gas at a flow rate of 50mLper 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 1Isobutane 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 2µL,of Isobutane into the chromatograph,and record the chromatogram.Calculate the percentage purity by dividing 100times the Isobutane response by the sum of all of the responses in the chromatogram.
Auxiliary Information—
Staff Liaison:Karen A Russo,Ph.D.,Scientist
Expert Committee:(PA1)Pharmaceutical Analysis 1
USP28–NF23Page 3021
Phone Number:1-301-816-8379