Thermal extraction–two-dimensional gas chromatography–mass spectrometry with heart-cutting for nitrogen heterocyclics in biomass burning aerosols

A thermal extraction–two-dimensional gas chromatography–mass spectrometry (TE–GC–GC–MS) method with heart-cutting is developed for quantitatively assessing nitrogen (N)-bearing organic species (e.g., pyrrole, pyridine, nitriles, and amines) in aerosols emitted from agricultural fires. Pyrolysis of the constituents in the crop residue is a likely formation pathway for these compounds. An evaluation of the TE–GC–GC–MS method proficiency for them confirms low carryover (<1%), adequate recovery (84–100%), high reproducibility (<9% RSD), picogram method detection limits, and a linear dynamic range spanning four orders of magnitude. The 14 substances for which quantitative results are available are primarily heterocyclic aromatic N compounds that comprise 0.7% (w/w) of the total fine aerosol mass. The benefits of TE–GC–GC–MS versus conventional GC–MS methods for organic N species in aerosols may depend on the matrix and the target N analyte concentration in that matrix; for the biomass burning aerosol examined in this study, the former approach reduces the unresolved complex mixture and detects organic N species not seen with GC–MS. We show another advantage of TE–GC–GC–MS is that it adequately resolves the anhydro-sugar (e.g., levoglucosan), alkanoic acid, and substituted phenol molecules in the biomass burning aerosol without the use of methylation or trimethyl-silyl derivatizing agents.