This document describes the procedure for determination of oxygenated compounds from ambient air samples. This method was developed by the Northern Laboratory Branch (NLB), Organics section. For this revision, only three ethers are addressed. They are methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). All are possible oxygen additives to the Federal and State newly reformulated gasoline for the reduction of carbon monoxide auto emission.
SUMMARY OF METHOD
Ambient air is collected in SUMMA passivated stainless steel canisters using a Xontech 910A sampler. A detailed sampling procedure can be found in the MLD Quality Assurance Manual, Volume II, Appendix Q and in the U.S. EPA Method TO14.
A 150 cc ambient air sample is drawn from the pressurized canister by
the house vacuum with the aid of a mass flow controller to a cryogenic
sample trap. The trap is packed with silanized glass beads and cooled to
a sub ambient temperature (-150oC). A digital flow meter readout,
attached to the Gas Chromatogram (GC), provides a visual indication of
the proper sample flow during sampling. The concentrated sample in the
trap is thermally desorbed and transferred to a gas chromatograph. Subsequent
separation is accomplished with a pre column (DB-WAX) and an analytical
column (DB-1) joined by a column switching valve. Thepre column does the
preliminary separation as well as the moisture management. After all three
ethers are eluted out from the pre column onto the analytical column, water
and all other late elution compounds are switched to vent. The target components
eluting from the analytical column are then detected by a flame ionization
detector (FID). The desired peaks are identified by their characteristic
retention times, and quantitated in parts per billion by volume (ppb v)
by comparison to an external standard.