Organic Chemistry Section
Air Analysis

Section 1911: Reformulated Gasoline Compounds (RFG) in Ambient Air

Revision 3.1 (August 1, 2003 - present)

1911.1 Scope and Application

This method is appropriate for the analysis of various VOCs in ambient air, specifically those found in reformulated gasoline. The method includes the specific parameters listed below, but may be adapted to similiar compounds.

Compound
 Report Limit (ppbC)
ethylene
 <0.10
acetylene
 <0.10
n-butane
 <0.10
ethanol
 <10.
isopentane
 <0.10
methyl tertiary butyl ether (MTBE)
 <0.10
ethyl tertiary butyl ether (ETBE)
 <0.05
benzene
 <0.05
toluene
 <0.05
ethylbenzene
 <0.05
m/p-xylene
 <0.10
o-xylene
 <0.05

1911.2 Summary of Method

This method incorporates a two stage concentration process which starts with 600mL of sample being passed through a glass bead cryotrap, cooled to -165 °C with liquid nitrogen, which traps the C2 and heavier hydrocarbons, reducing the sample volume to less than one milliliter. The cryotrap is then heated slowly to approximately 8 °C to transfer the hydrocarbons of interest to the cryofocuser, while leaving the majority of the water behind. (A nafion dryer cannot be used because it may remove the oxygenates.) The cryofocuser consists of a piece of guard column located at the injection port, which is cryogenically cooled to approximately -195 °C. the cryofocusing further reduces the sample volume to less than one microliter for injection. The guard column is rapidly heated (independently of the analytical column) and the sample is injected onto a gas chromatograph equipped with a DB-1 capillary column and a combination photoionization/flame ionization detector (PID/FID). The resultant separated components are quantitated using the FID, while using the PID as qualitative confirmation.

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Last updated 11/13/03