Forensic Chemistry: ILR Extraction (SPME, Charcoal Strip, ASTM Standards)

This mock drill covers the laboratory methods used to separate and identify ignitable liquid residues (ILR) from fire debris, a core topic in UGC-NET Forensic Science Paper II Unit VI. The four ASTM-recognised extraction techniques are examined in depth: passive headspace concentration with activated charcoal strip (ASTM E1412-19), passive headspace SPME with a PDMS 100-micrometre fibre (ASTM E2154-15), dynamic headspace purge-and-trap on a Tenax sorbent (ASTM E1413-19), and direct solvent extraction with pentane or hexane. Each method is tested at the operational detail level that routinely appears in examinations: incubation temperature and time, desorption solvent identity (CS2 for ACS), thermal desorption conditions for SPME, sorbent type for dynamic headspace, and the sensitivity trade-off that makes ACS the preferred choice for trace residues. GC-MS identification under ASTM E1618-19 is tested separately from the extraction step, as the ASTM E30 committee structures them, including the nine ignitable liquid classes and the substrate blank comparison requirement.

This mock is designed for UGC-NET Paper II aspirants, NFSU MSc and MSc Forensic Chemistry students, CFSL and state FSL trainees, and candidates preparing for FACT and GCFA-equivalent practical knowledge assessments. Sample-container selection (new metal paint cans versus polyethylene bags versus glass jars with metal lids), cross-contamination prevention protocols, and the handling of compromised-seal evidence under BNSS Section 176 are tested in scenario form. Substrate interference from burned carpet (SBR latex producing styrene and alkylnaphthalenes), polyurethane foam (TDI pyrolysis series), and pine wood (lignin-derived guaiacols and cellulose-derived furfurals) are tested in the interpretation section, mirroring real CFSL casework decisions.

Topics covered:

• Activated charcoal strip method: 16 h at 60 degrees Celsius, CS2 desorption, ASTM E1412-19
• SPME PDMS 100-micrometre fibre: 15-30 min equilibration, thermal GC desorption, ASTM E2154-15
• Dynamic headspace purge-and-trap: Tenax sorbent, thermal desorption, ASTM E1413-19
• Direct solvent extraction: pentane/hexane, matrix co-extraction limitation
• ASTM E1618-19: nine ILR classes, substrate blank comparison, reference standards
• Fire-debris container selection: metal cans vs polyethylene permeability
• Cross-contamination prevention: glove and tool discipline at each collection point
• Substrate pyrolysis interferences: carpet, polyurethane foam, pine wood
• CFSL workflow: BNSS Section 176, reference standard comparison, report conclusions

Allow 30 minutes.