Recovery and detection of ignitable liquid residues from the substrates by solid phase microextraction – direct analysis in real time mass spectrometry

• Volatile and less volatile marker compounds of ILR were detected by SPME-DART-MS. • The SPME extraction condition was optimized by the response surface method. • The method was applied to reanalyze the ILR in the samples after GC/MS analysis. In this study, direct analysis in real time mass spectrometry (DART-MS) was coupled to the solid phase microextraction (SPME) to extract and analyze the ignitable liquid residues (ILR) present in the sample matrices. The SPME extraction parameters, such as extraction temperature and extraction time, were optimized using a two-factor central composite design. The SPME-DART-MS setup was utilized to analyze the substrates and fire debris matrices spiked with gasoline. The results indicate that the less volatile marker compounds from gasoline were recovered from the substrates and fire debris, and their profiles matched well with the gasoline liquid samples analyzed directly by DART-MS. As expected, the effective extraction of marker compounds in gasoline required a relatively high temperature, i.e., 150 ℃. In the presence of a matrix, a higher extraction temperature and longer extraction time could benefit the extraction efficiency. The desorption of ILR on SPME fiber was performed by inserting the fiber into the DART-MS helium gas stream at 300 ℃ for 1 min with no carry-over residues being observed between successive samples. The chemical information attained with this method is typically not observed in the current GC/MS-based practice. The SPME-DART-MS was also extended to reanalyze less volatile components of ILR on substrates after the ASTM E1412 activated charcoal method, which indicates its possible application subsequent to the traditional GC/MS ILR analysis. The SPME-DART-MS has shown promise in ILR detection as an important complementary tool.