Forensic Toxicology: Sample Collection and Preservation

This mock covers the practical sample-collection and preservation layer of forensic toxicology — the part of the syllabus that decides whether the laboratory result will hold up in court at all. Thirty questions on what to collect, when, into which tube, with which preservative, why, and how to keep the chain of custody intact, at the depth expected of a first-year MSc Forensic Science student or a FACT / UGC-NET aspirant. The matrices section moves from antemortem (whole blood, serum, plasma for DUI; urine for workplace screens; oral fluid for roadside recent-use; hair for longitudinal exposure) through the full postmortem suite (femoral blood preferred over central, vitreous humour for ethanol confirmation and postmortem-interval estimation by potassium, gastric contents for evidence of oral ingestion, liver as a basic-drug reservoir, bile for opiate glucuronides, brain for inhalants and lipophilic CNS drugs, bone marrow and nail in skeletal cases). A dedicated cluster covers postmortem redistribution (PMR) — the central:peripheral ratio concept, why femoral blood is the gold-standard postmortem specimen, and the drugs (TCAs, digoxin, fentanyl, lipophilic basic drugs) most notorious for PMR.

It is pitched at BSc and first-year MSc forensic science students at NFSU, LNJN-NICFS, and other Indian universities, and at FACT, FACT Plus, and UGC-NET aspirants who need the sample-handling fundamentals locked in before tackling the analytical-chemistry papers. Sample collection is one of the highest-yield exam topics in Indian forensic-toxicology papers because every mistake here invalidates everything downstream.

Themes covered:

• Antemortem matrices — whole blood, serum, plasma for DUI; urine for workplace screens; oral fluid for recent use; hair for longitudinal exposure
• Postmortem matrices — femoral blood, vitreous humour, gastric contents, liver, bile, urine, brain, bone marrow / nail in skeletal cases
• Postmortem redistribution — central:peripheral ratios, drugs notorious for PMR, why femoral blood is preferred
• Preservatives — sodium fluoride 1% w/v (anti-glycolysis, anti-microbial), potassium oxalate (anticoagulant), EDTA for haematology and DNA
• Storage temperatures — 4 °C short-term, -20 °C archival, -70 °C for labile compounds
• Containers — glass with butyl-rubber septa for volatiles, headspace minimisation, light-protected amber glass for photolabile drugs
• Chain of custody, tamper-evident seals, labelling, transport in cool boxes
• Special scenarios — alcohol-case cross-checks (vitreous, n-propanol, EtG/EtS), CO with COHb on sealed blood, cyanide with urgent or frozen analysis, inhalant-abuse on sealed glass

Each question carries a detailed 220+ word explanation citing standard references — Modi's Textbook of Medical Jurisprudence and Toxicology (26th ed.), Karch & Drummer's Pathology of Drug Abuse (5th ed., CRC 2015), Levine's Principles of Forensic Toxicology (5th ed., AACC 2020), Cooper & Negrusz's Clarke's Analytical Forensic Toxicology (2nd ed.), the SOFT/AAFS Forensic Toxicology Laboratory Guidelines, the Society of Hair Testing consensus, SWGTOX standard practices, NAME forensic-autopsy standards, the EU DRUID project, SAMHSA workplace-drug-testing guidelines, Garriott's Medicolegal Aspects of Alcohol, Madea's Estimation of the Time Since Death, and the foundational Pounder & Jones 1990 paper on postmortem redistribution. Allow 15 minutes; the explanations are long enough to use as study notes by themselves.