Forensic Toxicology

Toxicology

What can chemistry tell us about drugs and poisons in the body

Sample

What do we have?

Blood

Urine

Hair

Tissue

Analysis

What is present?

Alcohol

Drugs

Poison

Metabolites

Interpretation

What does it mean?

Presence/Absence

Concentration

Effects

Significance

Forensic Toxicology Cases

Corners Death investigations

Impaired Driving

Sexual Assault

Fire death

Homicide

Screening Methods Used for Toxicology

Gas Chromatography/Mass
Spectrometry (GC/MS)
Head-Space GC analysis for volatiles
Quadrupole Time-of-Flight MS (QTOF

Targeted/Quantitation Methods Used in Toxicology

Gas Chromatography (GC)
Liquid Chromatography-Mass
Spectrometry (LC-MS/MS)
Head-Space GC analysis for volatiles

Parent Drug

Original Compound

Metabolite

Compound produced when the body processes a drug

Example cocaine goes from 1 to 3 compounds when ingested

Postmortem Redistribution

Changes in drug concentration after death due to movement of drugs between tissue and blood

Concentration measured after death may not equal concentration at the time of death
Some drugs are more affected than others
Sampling location matters
Peripheral blood, such as femoral blood, is often preferred for interpretation

Analyzing Blood

Drug Concentration

Often most useful for relating concentration to effects

Analyzing Urine

Drugs and Metabolites

Useful for evidence of prior exposure

Poor indicator of current impairment

Analyzing Vitreous Humor

Fluid from the eye

Relatively protected matrix

Useful post-mortem

Analyzing Hair

Longer detection window

Shows historical/repeated exposure

Analyzing Tissues

Liver, brain, kidneys etc.

Particularly important postmortem

Toxicology Workflow

Sample —> Screen —> Identify —> Quantify —> interrupt —> Report

Immunoassay

A screening method that uses antibodies to detect drugs or metabolites in a biological sample

Why use it? - Rapid

- Tests multiple drug classes at once

- requires relatively small sample

- useful for initial screening

Limitations - Cross-reactivity with similar compounds

- Uses a defined cut-off

- May detect drug class instead of specific drug

- False positives

- Positive results may require confirmatory testing

LC-MS (Liquid Chromatography Mass Spectrometry)

LC- Separates mixture into components (Picture)

MS- Identifies and graphs what each component is (Graph)

LC-MS/MS

Identifies it twice

Breaks down each component farther

Detection

Was the substance present?

Drug or metabolite identified

Evidence of exposure

Does not establish its effect

Impairment

Was the individual affected?

Depends on - Concentration

- Timing

- Tolerance

- Metabolism

- Other drugs/alcohol

- Individual variability

Cause of Death

Did the substance contribute to death?

Consider - Toxicology results

- Autopsy findings

- Medical history

- Drug interactions

- Circumstances of death

Putting Evidence Together

Toxicology- Example: Cocaine detected in blood 1.3mg/L

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Pathology- Underlying non-ischemic cardiomyopathy (Medical Condition)

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Case Circumstances- Sudden medical distress followed by cardiac arrest

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Cause of death- Toxic affects of cocaine in a person with non-ischemic cardiomyopathy