Forensic Chemistry: Fibre Identification with FTIR, Raman and PGC-MS

This medium-difficulty UGC-NET Forensic Science Paper II Unit VII drill covers the forensic identification of textile fibres using polarising microscopy, FTIR spectroscopy, Raman spectroscopy, pyrolysis-GC-MS (PGC-MS), and microspectrophotometry (MSP). Questions range from natural fibre morphology (cotton bilobate cross-section, wool cortex-cuticle structure, silk triangular cross-section, linen node intervals) through synthetic polymer fingerprinting (nylon 6 caprolactam vs nylon 6,6 hexamethylenediamine pyrolysates; PET ester carbonyl at 1712 cm-1 vs PBT at 1711 cm-1; acrylic polyacrylonitrile nitrile stretch at 2240 cm-1; polypropylene CH2 rocking doublet) to dye-class discrimination by HPLC and TLC. SWGMAT fibre sub-group guidelines structure the comparison hierarchy: class determination by FTIR and PGC-MS, followed by subclass by Raman and MSP for dyed fibres, then colour comparison. Birefringence values and sign of elongation distinguish cotton (positive, low birefringence) from linen (positive, higher birefringence) and wool (nearly isotropic under polarised light), which are the near-neighbour distractors most frequently tested. The CFSL Kolkata trace-evidence section follows Robertson and Grieve's tiered comparison protocol and ASTM E2227 for fibre examination terminology.

Aimed at UGC-NET Forensic Science Paper II aspirants covering Unit VII (Fibres and Textile Fibres), NFSU MSc Forensic Chemistry students, FACT aptitude candidates, and CFSL and state FSL scientists rotating through the trace-evidence section. Core references are Robertson and Grieve (Forensic Examination of Fibres, 2nd ed.), Houck and Siegel (Fundamentals of Forensic Science, 3rd ed.), Saferstein (Criminalistics, 12th ed.), and the SWGMAT fibre examination guidelines.

Topics covered:

• Natural fibres: cotton, wool, silk, linen, jute morphology and cross-section
• Synthetic fibres: nylon 6 vs 6,6, PET, acrylic, polypropylene
• Polarising microscopy: birefringence, sign of elongation, refractive indices
• Cross-sectional shape: bilobate cotton, round wool, triangular silk
• FTIR: amide I/II bands, ester C=O, nitrile stretch, CH2 rocking
• Raman spectroscopy for dyed fibre subclass discrimination
• Pyrolysis-GC-MS: polymer-specific pyrolysate fingerprints
• Dye analysis: TLC, HPLC, microspectrophotometry
• Fluorescence microscopy for optical brightener and dye comparison
• Transfer and persistence principles in fibre casework

Work through each question before reading the explanation, then revisit errors against the Robertson and Grieve, Saferstein, Houck and Siegel, and SWGMAT citations. Allow 30 minutes.