DI-SPME method for the analysis of fire accelerants in simulated fire debris samples using GC/MS and GC×GC/Q-TOFMS

Climate change has intensified droughts and heatwaves, increasing wildfire frequency and the release of hazardous pollutants that threaten ecosystems, human health, and air quality. Selective and sustainable analytical methodologies are therefore required for forensic and environmental investigations. One of the most common methods for fire debris analysis is headspace solid-phase microextraction (HS-SPME); however, this approach is limited in its ability to capture low-volatility analytes, typically lost during combustion. Here, an alternative strategy integrating direct immersion solid-phase microextraction (DI-SPME) with comprehensive two-dimensional gas chromatography (GC × GC) is proposed for fire debris analysis. A novel PTFE fiber-protection device consisting of a perforated cylindrical tube was developed to prevent fiber damage by coarse particles while allowing analyte diffusion, extending fiber lifetime and eliminating solvent-based solid-liquid extraction. Simulated fire debris samples prepared from office paper spiked with gasoline and diesel were analyzed after combustion and aqueous extraction with ethyl acetate as a modifier. Method validation was performed using linear alkanes (C14-C18) as marker compounds for flammable liquids. GC/MS parameters were optimized using Central Composite Design, whereas GC × GC/Q-TOFMS conditions were screened using a fractional factorial design. The method showed high sensitivity (LOD 2.92-85.70 μg L^-1) and satisfactory intra- and inter-day precision (6.8-25.4%). The approach aligns with green chemistry principles by reducing solvent consumption and analysis time while enabling automation and miniaturization. The combination of simplified sample preparation, high-resolution separation, and multivariate analysis supports reliable accelerant fingerprinting for forensic and environmental fire investigations.