2005 Progress Report: Application of Thermal Desorption GCMS (TD-GCMS) for the Analysis of Polar and Non-Polar Semi-Volatile and Particle-Phase Molecular Markers for Source AttributionEPA Grant Number: R831088
Title: Application of Thermal Desorption GCMS (TD-GCMS) for the Analysis of Polar and Non-Polar Semi-Volatile and Particle-Phase Molecular Markers for Source Attribution
Investigators: Schauer, James J. , Sheesley, Rebecca J. , Simoneit, Bernd R.T.
Institution: University of Wisconsin - Madison , Oregon State University
Current Institution: University of Wisconsin - Madison
EPA Project Officer: Chung, Serena
Project Period: January 1, 2004 through December 31, 2006 (Extended to December 31, 2007)
Project Period Covered by this Report: January 1, 2005 through December 31, 2006
Project Amount: $449,687
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
The overall objective of this research project is to fully develop, validate, and employ a cost-effective thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) technique for the analysis of semi-volatile and particle-phase organic compounds, which can be applied to both atmospheric and source samples.
Year 2 efforts on the TD-GC-MS included completing analysis on a full year of daily samples from the St. Louis Supersite and the development and implementation of a TD-GC-MS diazomethane method.
The nonpolar TD-GC-MS method analyzes a limited set of organic compounds including alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes. A full year of fine particulate matter (PM2.5) samples collected at the St. Louis Supersite have been analyzed using this method. The Supersite data will be incorporated in a large positive matrix factorization (PMF) study of sources impacting St. Louis. The nonpolar TD-GC-MS method has proven to be very robust for large datasets and will continue to be of use for projects that focus on motor vehicle emissions and other predominantly nonpolar sources.
The primary focus of this grant work is the inclusion of the polar compounds into the TD-GC-MS method. So far, two different derivatization techniques have been evaluated and employed. A silylation method allows the quantification of levoglucosan, cholesterol, and a variety of simple carbohydrates with low uncertainty. The silylation TD-GC-MS method, however, was proven to be infeasible for large projects because of the strain of the method on the TD and GC-MS instruments. The second derivatization method, a diazomethane method, allowed a variety of acids, including alkanoic acids and aliphatic and aromatic diacids, to be measured. The TD-GC-MS diazomethane method is significantly less demanding on the TD and GC-MS instruments and readily amenable for large sampling sets as compared to the silylation method.
Development of the combined polar and nonpolar method has been developed using the diazomethane derivatization, which only required minor modification to the nonpolar TD-GC-MS method. TD-GC-MS now is being used for other projects at the University of Wisconsin at Madison, including the Study of Organic Aerosols at Riverside (SOAR) project, which collected samples in Riverside, California, during August 2005; the Megacities Impact on Regional and Global Environment-Mexico project that collected samples in Mexico City during spring of 2006; and samples from the Southern California Particle Center. Analysis of the SOAR samples is underway. The high time resolution sampling protocol for the SOAR study was designed with the enhanced detection limits of the TD-GC-MS in mind. Four successive samples were collected each day of the sampling event to capture morning rush hour, the middle of the day, evening rush hour, and overnight events. As with the nonpolar analysis, rigorous QA/QC protocols are being implemented with the analysis of the SOAR samples, including check standards after every five samples to validate the calibration curve, blanks between samples to eliminate cross contamination, duplicate samples, and matrix spikes of standards onto filter samples to assess recovery.
As the diazomethane method now is fully established, efforts are being directed at alternative derivatization techniques to further expand the range of compounds that can be measured by GC-MS. A modified silylation method is being explored in addition to other derivatization agents including: (1) N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide for the analysis of oxalic acid and malonic acid; and (2) O-(2,3,4,5,6-pentafluorophenyl) methylhydroxylamine hydrochloride for the analysis of carbonyl compounds that are important components of secondary organic aerosols.