Montana State University

Department of Chemistry and Biochemistry

Research Projects

Knighton Group Overview

Dr. Knighton has been actively involved in the development and application of chemical ionization mass spectrometry for nearly 20 years. That interest continues today and is primarily focused on using drift tube reaction mass spectrometry for the quantification of trace level volatile organic compound (VOC) emissions from a wide variety of natural and anthropogenic sources. A significant fraction of this research effort involves field work where a proton transfer mass spectrometer (PTR-MS), a commercially produced drift tube reaction mass spectrometer, has been used to measure selected volatile organic trace gases in the ambient atmosphere and in the emissions from vehicles and aircraft. The PTR-MS instrument merges the concept of chemical ionization with that of the swarm technique of flow-drift tubes. Chemical ionization is based on H3O+ as the primary reagent ion, which does not react with the major components of clean air, but does react with most non-alkane VOC's via proton transfer reactions. The electric field used to transport the ions through the drift tube also provides sufficient additional energy to the ions to discourage association reactions with water molecules that are always present in any real sample. The selectivity provided by chemical ionization, control of unwanted hyfration reactions by using drift tube coupled with the sensitivity of mass spectrometry detection makes the PTR-MS a powerful analytical tool capable of rapid in-situ measurement of trace chemical species with proton affinities greater than that of water. Because the PTR-MS provides sensitive (sub-ppbv) real-time (~1 second) measurement of selected hydrocarbon components, it is ideally suited for monitoring systems that have rapidly changing chemical composition like that of engine exhaust emissions. The MSU PTR-MS system has been deployed in a wide variety of field programs including the measurement of aerosol trace gas precursor species in jet engine exhaust in the Aircraft Particle Emissions eXperiment (APEX)-2004, APEX2-2005 and APEX3-2005, on-board the Aerodyne Mobile Laboratory for the measurement of selected VOC's in Mexico City Urban Air Quality field measurement campaigns of 2002, 2003 and 2006. In addition, we have used the PTR-MS technique in the study of a diverse set of matrices including the monitoring of flavor compounds in human breath, volatile emission products of an endophytic fungus, Muscodor Albus, and those released from softwood lumber during the kiln drying process.

Personnel:
W. Berk Knighton

Keywords:
Analytical, Spectroscopy