Comparison of Three Analytical Methods for the Determination of Methanol in Vehicle Evaporative and Exhaust Samples 930377

In an effort to reduce ambient ozone and carbon monoxide levels, the U.S. Environmental Protection Agency has mandated the use of oxygenated fuels under the Clean Air Act. These fuels may contain varying amounts of methanol, ethanol, or other alcohols, and ethers. The current reference method for the analysis of methanol in vehicle emissions involves sample collection with impingers that contain water and the subsequent analysis of this aqueous solution by gas chromatography/flame ionization detection (GG/FID). The impinger method is problematical in that it is both time consuming and inconvenient in a test facility in which it is the only “wet” chemical method employed. In response to this problem, two alternative “non-wet” methanol methods were evaluated against the impinger method and against each other.

The first alternative method employed a switched two-column GC/FID analysis of gaseous samples. This method determined the C₁ through C₄ alcohols, methyl and ethyl t-butyl ethers (MTBE and ETBE). Tedlar bag samples were introduced to the GC/FID with a sample loop. The second alternative method analyzed the diluted vehicle exhaust in both real-time and integrated bag samples by Fourier transform infrared spectroscopy (FTIR).

These three methods were compared using exhaust samples containing varying methanol concentrations from a variety of alternatively fueled vehicles. Within the analytical range of each method, there was good agreement among the three methods The alternative GC method using the sample loop introduction technique had an instrumental detection limit of 0.02 ppm methanol, whereas the impinger method had a detection limit of 0.05 ppm. The FTIR analysis had a detection limit of 0.1 ppm. For actual samples, all of the methods had quantitation limits of 1 ppm methanol.