Toxicologists & Drug AnalysisToxicologists & Drug Analysis

Describe techniques that

forensics toxicologists use to isolate and identify drugs and poisons.

Objectives

Use TLC, GC, Immunoassay Immunoassay – very different

Based on specific drug antibody reactions

Ability to detect small concentrations

Best for detecting marijuana

Screening Tests

GC/MS

One step test of unequaled sensitivity and specificity

Drug testing not related to criminal matters

Confirmation Tests

Drugs remain in

Bloodstream – 24 hours Urine – 72 hours

Tested in Private labs, typical for workplace screenings

Hair nourished by blood flowing through capillaries near root Drugs diffuse through capillary walls and become

permanently entrapped in hair’s protein structure Drug’s location becomes historical marker for

delineating drug intake

Drugs in Hair

Group of poisons

Arsenic, Bismuth, Antimony, Mercury, Thallium Reinsch Test

Dissolve body fluid or tissue in hydrochloric acid solution then insert copper strip to solution

Appearance of silver or dark coating on copper indicates presence of heavy metal

Confirm with inorganic analysis

Heavy Metals

One of the most common poisons Primarily absorbed by red blood cells

Combines with hemoglobin to form carboxyhemoglobin

Not enough hemoglobin left to carry oxygen to tissues

Causes asphyxiation

Carbon Monoxide

Spectrophotometric – visible

spectrum GC – liberates CO from blood Calculate percent saturation

Greater than 50-60% = fatal Fatal levels can be lower when in

combination with depressants

2 Basic Methods for Detection of CO

High levels of carbon monoxide in

blood indicate that victim breathed in products of fire and was alive when fire began

Low levels = dead before fire started Could have been placed there to

destroy evidence

Arson Victim

Interpreting results is the most

difficult chore Blood concentration levels can

be used to estimate pharmacological effects of drugs

Significance of findings

Before drawing conclusions,

toxicologists must consider other factors – age, physical condition, drug history, tolerance Prolonged use can make an individual less

responsive to drug’s effects Additive or synergistic effects provided by

interaction of 2 or more drugs

Significance of findings

Concentration in urine is poor indicator

because formed outside circulatory system and drug levels can build up over long periods of time Drug can be found in urine 1-3 days after

taken and long after other effects have disappeared

Best used to corroborate other findings

1970s, LAPD developed and tested

clinical and psychophysical examinations that police officers could use to identify and differentiate between types of drug impairment

Evolved into national program Standardized methods Not a substitute for toxicology testing

Drug Recognition experts (DRE)

1. What is the difference between a screening test and a confirmation test?

2. What are the three screening tests most widely used for forensic toxicology? What is the confirmation test of choice?

3. Which of the following is not classified as a heavy metal?A. LeadB. ArsenicC. MercuryD. Thallium

4. Explain how inhaling carbon monoxide can cause death.5. Name at least three factors in addition to blood

concentration levels that must be considered before drawing conclusions about a subject’s drug induced behaviors.

6. Why is the concentration of a drug present in urine a poor indicator of how extensively an individual’s behavior or state is influenced by the drug?

10.7 Questions