Development of a Novel Approach to the Collection, Speciation, and Quantification of Semi-Volatile Hydrocarbons in Diesel Engine Emissions, 08-9498

Principal Investigators
Joseph Pan
E. Robert Fanick

Inclusive Dates:  07/01/04 – Current

Background - The gas phase of diesel engine exhaust emissions has not been thoroughly studied, primarily because of the complexity of the diesel fuel. Currently, most of the materials collected from the gas phase of diesel engine exhaust emissions are the unburned diesel fuels. Unlike gasoline, which has been thoroughly analyzed and most components identified, diesel fuel is much more complicated because its components have larger numbers of carbon and hydrogen elements than does gasoline. This makes it more difficult to identify the components in diesel fuel and diesel engine exhaust emission samples. The conventional sampling media for the gas-phase engine exhaust emission has been PUB/XAD-2/PUF (polyurethane foam/XAD-2 synthetic resin). Unfortunately, these materials are difficult to clean, especially the PUF. The background PUF-caused signals prevent detection of the low limits. These low limits continue to be a requirement of stringent regulations. According to current published literature, the quantification of the target SVHC (semi-volatile hydrocarbons) is largely performed using the external standard method, which fails to compensate for losses during the extraction and blow-down processes.

Approach - Four different sampling methods are being tested for sample collection, including the hexane impinger, cold trap, XAD-2, and the Empore™ membrane methods. To trap the SVHCs, the cold trap method uses the coldness of the 2-propanol/dry-ice bath, while the hexane impinger method uses chilled hexane. The XAD-2 method uses glass cartridges packed with XAD-2 resin to trap SVHCs. A special SAD-2 holding design is used so that the entire XAD-2 glass cartridge can be inserted into the Soxhlet extractor. Doing away with the transfer of XAD-2 into a Soxhlet extractor eliminates potential losses caused by that transfer. The Empore™ membrane was originally developed for solid-phase extraction of hydrophobic pollutants from water samples, but it has also been shown to have potential for trapping hydrophobic pollutants in air samples.

In SVHC speciation, a 60-meter DB-5 column has been used to maximize the separation of the SVHCs. An Agilent 5973N MSD has been used to identify diesel fuel components as well as the diesel engine exhaust emission samples in both EI/PI (electron impact/positive ion) mode and CI/PI (chemical ionization) mode, using methane as chemical reagent gas. With some exceptions, the chemicals in the samples are being identified as chemical types instead of specific isomeric chemicals. Relative retention time windows of identified chemical types are being established, with as many as 110 different chemical types for the diesel fuel and the diesel emission samples. Representative authentic standards for most chemical types have been acquired for accurate quantification; as many as 45 deuterated SVHCs have been acquired to facilitate the internal standard method of quantification. A mixture of these internal standards is placed into the emission samples at the beginning of extraction.

Accomplishments - This project is ongoing. Accomplishments will be announced at a later date.

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