Use of GCxGC-ToFMS and the third order advantage for compound-specific stable isotope analysis of Polycyclic Aromatic Hydrocarbons in particulate matter

CARLOS MANZANO (1), Wentai Luo (2), James Pankow (2), Robert Synovec (3), Staci Simonich (1)

(1) Oregon State University, Corvallis (2) Portland State University, Portland (3) University of Washington, Seattle

     Abstract Number: 450
     Last modified: May 12, 2010

Abstract
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous to the environment; they originate from incomplete combustion of organic matter during energy and industrial processes. Natural sources such as forest fires and volcanic eruptions also produce PAHs. The sources and environmental fate of PAHs have been the subject of extensive studies due to the carcinogenic and/or mutagenic properties of some of their isomers [1,2,3].

Source identification of PAHs using their molecular compositions has been partially inconclusive because it depends on factors such as source material, burning temperature, air/fuel ratio and environmental alteration during transport. One of the ways to predict the sources of individual PAHs isolated from various environments samples is the measurement of compound-specific stable carbon-isotope compositions because it is expected to reflect that of the original organic matter subjected to combustion [1,4].

To avoid clean-up steps and the associated sample loss sample loss associated with Combustion Isotope Ratio Mass Spectrometry (C-IRMS), a method based on chemometrics was used. Standard solutions of PAHs were analyzed by GCxGC-ToFMS, which provides third order data due to three independent dimensions of analysis (e.g. first column, second column and mass spectra).

This data has the advantage of allowing mathematical resolution of an analyte from interfering compounds using only one chromatogram, commonly referred as the “third order advantage” [5]. Algorithms such as parallel factor analysis (PARAFAC) are often used for this purpose [6,7,8,9]. The GCxGC-ToFMS system provides a combined $^(12)C and $^(13)C analyte peak as part of the third order data cube. This peak is isolated from interfering compounds and noise based on the third order advantage with PARAFAC. The combined mass spectra are then mathematically resolved using Classic Least Squares (CLS) providing a $^(12)C:$^(13)C ratio [5]. We applied this method to the measurement of PAHs in particulate matter.


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