LECTURE 16: FORENSIC CHEMISTRY

Question 1

What are the key challenges that face any forensic practitioner/laboratory?

Answer 1

• Chain of custody (forensic register)
• Sample integrity
• Personal integrity (eg. police clearance)
• Quality of analysis (ie. reliability of result)

Question 2

Toxicology and types

Answer 2

• analysis of drugs and poisons in biological tissue

types include: coronial, sobriety, criminal and private

Question 3

Coronial Toxicology

Answer 3

• Samples obtained post-mortem
• Sudden and unexpected deaths (eg. suicide, traffic, murder)
• Although COD may be obvious at the time of PM, samples may still be sent to toxicology for analysis
• Aim: To detect, identify and measure the presence or confirm the absence of a substance, thereby assisting the forensic pathologist in determining whether the presence or absence of the substance has contributed to the cause of death. Examples:
  • Overdosage (ie. therapeutic vs. toxic)
  • Drugs in a traffic death (eg. Cannabis or benzos)
  • Confirmation of an anti-epileptic (eg. Sodium valproate)

Question 4

Sobriety Toxicology

Answer 4

• Samples taken by WA Police under Road Traffic Act
• Blood, urine and oral fluid
• Samples taken from motor vehicle drivers suspected of being under the influence of drugs/alcohol
• Aim: To identify the presence of alcohol or other drugs that may cause impairment and quantify where necessary.
• Examples
  • Alcohol in driver of a single MVA (insurance)
  • Amphets in driver of a major crash
• Blood may be obtained when:
  • Driver opts for blood over breath (alcohol)
  • Driver opts for blood over saliva (drugs)
  • Driver unable to provide breath/saliva
  • Breath test results incongruent with driver behaviour
• Roadside Drug Testing
• In operation since late 2007
• Portable drug-testing devices
• “Random” testing
• Prescribed Illicit Drugs:
  • Methamphetamine (ie. speed, ice, crystal meth)
  • Methylenedioxymethamphetamine (ie. MDMA, ecstacy)
  • Tetrahydrocannabinol (ie. THC, cannabis)

Question 5

Criminal Toxicology

Answer 5

• Samples received from WA Police (FACT)
• Samples from POI and/or victim
• Eg. DFSA, sexual assault, murder, assaults
• Blood - Urine - Liquids/residues (eg. cans of drink)
• Aim: To confirm the presence or absence of a drug(s) in a POI or victim, and/or confirmation of the alleged crime committed (eg. “drink spiking”)
• Examples:
  • Amphetamines in an accused murderer
  • GHB in a sexual assault victim
  • Cyanide in juice

Question 6

Fibres

Answer 6

• Comparison analysis: Comparison of fibres can provide a link between items/people. Examples:
  • Fibres from a suspect’s jumper and a fibre at the scene
  • Fibres from carpet at the scene on a suspect

Question 7

Glass

Answer 7

• Comparison analysis: Comparison of glass fragments can link a person or item to a place/vehicle
• Refractive Index
  • Glass fragments can be compared using RI
  • Glass mounted in silicone oil and will be visible when there is a difference in RI
  • The RI of the oil varies with temperature
  • Temperature varied until the glass “disappears” (ie. the RI of the oil and glass are the same)
  • The match temperature is compared using statistics
• Elemental Analysis
  • Comparison of elements (eg. from manufacture)

Question 8

Gunshot residues

Answer 8

• Gunshot residues (GSR) are produced when a gun is fired
• Originate from primer and propellant
• GSR particles may have a characteristic composition and/or morphology
• Identification:
  • SEM-BSE
  • SEM-EDX
  • Pb, Sb, Ba - lead, barium, antimony

Question 9

Paint

Answer 9

• Comparison: Comparison of paint samples can link two people/items. (eg. A car and a hit and run victim

Question 10

Marquis Test

Answer 10

• Chemical spot test for unknown powders
• Marquis Reagent (CH2O + H2SO4)
• Colour change indicates type of compound
  • Brown/orange = amphetamine
  • Purple = opiate
  • Black/dk blue = ecstasy

Question 11

TLC is a presumptive test for what in what

Answer 11

THC (tetrahydrocannabinol) in cannabis