Evaluation and Improvement of Capillary Microextraction of Volatiles Coupled to Gas Chromatography-Mass Spectrometry for the Analysis of Ignitable Liquid Residues in Fire Debris
A key aspect of fire debris analysis is the ability to extract the remnants of an ignitable liquid from a matrix with a high degree of reliability and sensitivity. Although there are several robust, standardized methods, there is no single technique universally applicable to casework. In this work a novel extraction technique – Capillary Microextraction of Volatiles (CMV) – has been applied, for the first time, for ignitable liquid residue (ILR) extraction. A 20-minute dynamic sampling laboratory protocol from traditional 1 L paint cans was established and optimized based upon ASTM guidelines. The development of new adsorption phases for CMV use are also reported. A phenyl-modified sol-gel phase demonstrated up to 8-fold higher recoveries of BTEX compounds from headspace sampling compared to previously reported CMV phases and four additional differently functionalized phases were synthesized and evaluated. Preliminary comparisons of the CMV to activated charcoal strips (ACS) and to solid-phase microextraction (SPME) demonstrated equivalent or slightly higher extraction efficiency relative to SPME, and over two orders of magnitude greater extraction efficiency relative to ACS. The versatility of the CMV has also been extended to portable analytical instrumentation. The device was successfully coupled to a TRIDION-9 portable GC-MS when combined with a needle trap, and both were evaluated for their applicability to fire debris analysis. The CMV/NTD technique demonstrated extraction capabilities similar to the CMV alone; however, ILR analysis by the T9 was heavily impacted by the limited chromatographic resolution resulting in complicated data interpretation. The CMV was similarly coupled to a Griffin G510 for dual evaluation. Also presented for the first time is a field ILR headspace sampling protocol involving the use of a paper drinking cup. A five-minute sampling/extraction protocol was sufficient to recover six key gasoline analytes from a 0.01 µL spike of gasoline with typical mass recoveries of 4 – 24 ng. An overall 21-minute analytical method was developed using the CMV/Cup protocol capable of detecting several ILR-associated compounds at up to 10x greater sensitivity than traditional extraction techniques. This body of work demonstrates the overall versatility of the CMV as applied to the entire field of fire debris analysis
