2004 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, 2004 through December 31, 2005
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 objective of this research project is to fully develop, validate, and employ a cost-effective thermal desorption gas chromatography mass spectrometry (TD-GCMS) technique for the analysis of semi-volatile and particle-phase organic compounds, which can be applied to both atmospheric and source samples.
In combination with support from Electric Power Research Institute and the U.S. Environmental Protection Agency, a TD-GCMS method has been developed that measures nonpolar organic species, including polycyclic aromatic hydrocarbons, hopanes, steranes, and alkanes. These compounds have traditionally been analyzed by Dr. James Schauer and his group using a solvent extraction procedure followed by GCMS analysis. Despite the differences in sample preparation, both methods use the same instrument parameters for the GCMS analysis, the same internal standards, and the same quantification standards. By using the same parameters, there should be historical continuity with previously detailed organic analysis. To ensure this continuity, validation of the TD-GCMS method is being pursued by comparing results with the established solvent extraction technique developed by Dr. Schauer. Parallel analysis of a set of 100 daily samples from the St. Louis Supersite has been completed by the solvent extraction GCMS method and is in process for the TD-GCMS method. At this point, validation is in the data analysis stage. Within the next month, a comparison of the two methods will be complete for the nonpolar species previously mentioned. Additional validation is planned using matrix additions to further verify the recovery of the different nonpolar species. Once the method is validated, the remaining 400 daily PM2.5 samples from St. Louis will be analyzed.
A method for the analysis of polar species by TD-GCMS also is under development at the University of Wisconsin, Madison. This method derivatizes polar compounds directly on the filter prior to analysis by TD-GCMS. Derivatization is necessary to analyze compounds with alcohol functional groups, including species used in molecular marker source apportionment such as levoglucosan and cholesterol and simple carbohydrates like glucose, sucrose, and fructose. Acid species such as n-alkanoic acids, which are commonly found in the atmospheric PM, and aromatic acids, which have been implicated as tracers for secondary organic aerosol, also can be measured if derivatized. Preliminary validation has been done for the TD-GCMS analysis of simple carbohydrates, levoglucosan, and cholesterol using direct silylation derivation. This includes calibration curves of three dilutions of a standard and matrix addition. Preliminary testing on PM samples from the St. Louis Supersite indicate that the technique is effective in measuring these species in atmospheric samples. Direct derivatization using diazomethane followed by TD-GCMS analysis is being explored to quantify the acid species. When both of the derivatization methods have been more fully developed, they will also be validated by comparing parallel results with solvent extraction GCMS for daily samples from St. Louis.
The analysis of the daily St. Louis Supersite samples will provide a unique and comprehensive dataset of fine particle organic compound speciation for health studies by the Harvard School of Public Health and St. Louis University. In addition, by virtue of its size, the dataset will provide the first opportunity to compare different receptor modeling techniques that exploit organic tracers (molecular markers).
We will finish running the 500 daily filter samples from the St. Louis Supersite by the nonpolar method, validate the nonpolar method by comparing 20 percent of these results with solvent extraction results, finalize optimization and validation of the polar TD-GCMS method using a multistep derivatization, and begin to analyze 500 St. Louis samples for polar species.
Additionally, a 3-week sampling event is planned for July/August of 2005 in Riverside, California. PM2.5 filter samples will be collected every 4 hours during the day and analyzed for both polar and nonpolar organic species. This sampling event is being leveraged by other projects but may potentially meet the needs of the sampling project planned for Year 3 of the project in the San Joaquin Valley.
Source samples that were originally planned for analysis during Year 1 of the project will be gathered from existent projects and collaborators during Year 2 for analysis. These will include, for example, motor vehicle exhaust, residential fuel samples from Southeast Asia, jet engine exhaust, and secondary organic aerosols.
Initial development of samplers and TD-GCMS protocols for the collection and analysis of semivolatile organic compounds will begin in Year 2 of the project. Sorbent impregnated backup filters will be used for these species.