Criminalistics Exam 4

Two types of forensic toxicology

1. Human performance toxicology

2. Postmortem analysis

What is human performance toxicology

Measures the amount of alcohol or drugs in a living person’s blood or breath

Estimates their role in modifying human performance or behavior

What is postmortem analysis

Presence of drugs, gases, metals, and other toxic chemicals in human fluids and organs

Determines their role, if any, in the death

What is the most common type of human performance testing

Testing is done to determine if someone is driving a car under the influence of alcohol or drugs

What is BAC

Blood Alcohol Concentration, which expresses the amount of alcohol in a person’s body

Typically done by police officers

What is a field sobriety test

Assesses a driver’s degree of physical impairment

What are the effects of low BAC

Affects cerebral function

What are the effects of high BAC

Medullar function is affected

BAC levels

BAC < 0.06%: considered to be sober

BAC = 0.18%: individual is easily confused

BAC = 0.27%: person is in a stupor

BAC = 0.35%: they are in a coma

Where is alcohol mainly absorbed?

Ethyl alcohol is absorbed into the bloodstream largely from the stomach and small intestine

What are some factors that influence the rate at which alcohol enters the bloodstream

Rate of gastric emptying

Presence of food

Concentration of alcohol consumed

Type of beverage

Rate at which alcohol is consumed

How is alcohol eliminated from the body?

Two ways:

1. Oxidation: 95-98% of alcohol is eventually oxidized to CO₂ and water

2. Excretion: Normally as sweat, breath, and urine

What is the process of the oxidation-reduction reaction of eliminating alcohol

Alcohol is transported to the liver, where enzymes catalyze its oxidation

Acetaldehyde → acetic acid → CO₂ and H₂O

More than 90% of ethyl alcohol that enters the body is oxidized to acetic acid

How is BAC measured?

A breath sample is first collected at the scene. Then, a direct chemical analysis of a blood sample can be done, which is typically more reliable.

How are blood samples for measuring BAC collected

Skin is first cleaned with a nonalcoholic disinfectant (Betadine)

Blood is taken with a sterile needle

How are blood samples for measuring BAC preserved

Preservatives are added to the sample

• Anticoagulants (potassium oxalate)

• Sodium fluoride (NaF) inhibits microorganisms from growing and contaminating the sample

  • Indicated with a gray capped tub

• Refrigeration

What happens if a BAC blood sample is not preserved properly

BAC results will be abnormally low

How are BAC blood samples collected from cadavers

Blood samples should be collected from multiple sites

Tissues samples can be used instead as well

Explain the headspace technique

Theory: Concentration of ethanol and other volatiles in a dilute aqueous biological sample is directly proportional to their concentration in the gas phase

About 1/3 - ½ sample (liquid or solid) is placed in an airtight container

Headspace vapor is injected into the GC/FID using an airtight syringe

Each component has a unique retention time

Concentration is calculated by a calibration curve based on peak area or peak height

Uses ~ 100 uL of blood or other body fluids or 1-2 g of tissue

Dilutor will combine the sample with 450 uL of internal standard, which acts as a positive control (IS)

Explain gas chromatography

Used to separate and detect complex mixtures of volatile organic compounds

Distributes compounds of a mixture between an inert-gas mobile phase and a solid stationary phase

Components product symmetrically shaped peaks (Gaussian peaks)

Peak area is proportional to the concentration of that component

What does postmortem toxicology begin with

A case history of the deceased and analyses for poisons

How are toxicological collections of postmortem specimens done

Body fluids are collected from organs in which chemicals might accumulate

Collection is done before the body is embalmed

Analysis may also be done on bone marrow, fluid in the eye, hair, or maggots

Presumptive testing is performed first to detect the presence or absence of drugs

What are specifically analyzed first for postmortem toxicological specimens

If poison is taken orally, the GI contents are analyzed

Urine

Kidneys

Liver and other organ tissues

What are the general categories of poisons

1. Inorganic

2. Organic

3. Radiological

4. Biological

What types of poisons are typically analyzed in toxicology

Corrosive poisons

Metabolic poisons

Toxic metals

Organic metals

What are corrosive poisons

Substances that destroy tissues on contact (e.g., HCl, sulfuric acid, etc.)

What are metabolic poisons

Poisons that cause harm, and frequently death, by interfering with some essential metabolic process in the body

What are toxic metals

Metals that are toxic in very small amounts (e.g., lead, mercury, etc.)

What are organic poisons

Poisons that are typically administered to incapacitate a victim (e.g., laxatives, antidepressants, etc.)

What is pharmacology

The study of the relationship between drugs and living things

What is toxicology

The study of the nature, effects, and detection of poisons

What is pharmocokinetics

Study of how drugs move in and out of the body

Does the rate at which the body removes alcohol from the blood differ between individuals

Yes, it varies significantly between individuals

What is the equation for estimating BAC range

C_a= C_t + β(t)

C_a = BAC at time of the accident

C_t = BAC at time of blood draw

Lowest rate is β = 12.5 mg/100 mL hr

Highest rate is β = 25 mg/100 mL hr

t = time from accident to blood draw

What are the responsibilities of a forensic toxicologist

Identity of drugs

Quantity of drugs

Presence of metabolites

Interactions of present drugs

Role of dependence and tolerance

What are some challenges of forensic toxicologists

General screening'

May only have ug or ng of substances

Metabolites of substances

Toxicity levels → lethal doses

What specifically does pharmacokinetics look at

Absorption

Distribution

• Drugs may have a specific structure that causes them to accumulate in a particular tissue

Metabolism

• Process whereby a drug or other substance is chemically changed to a different form

Elimination

What are the main steps of analysis in forensic toxicology

Extraction

Screening

Confirmation

What are types of extraction

For liquids → acid/base extraction

For solids → Solid phase microextraction (SPME)

• Coated wire/fiber is inserted in fluid (activated charcoal)

• Drugs selectively absorb

• Wire is removed and drugs eluted

What are types of screening procedures

• Thin Layer Chromatography (TLC)

• Gas Chromatography

• Immunoassay

What is thin layer chromatography

The stationary solid phase involves a glass or plastic plate coated with a thin layer of silica

The moving liquid phase works through capillary action, causing the solvent to be pulled across the plate

Separates component based upon their affinity for the mobile and stationary phases

R_f = distance component traveled/distance solvent traveled

Explain ELISA

Enzyme-Linked Immunosorbent Assay

Involves microplates coated with a polyclonal antibody that has a high affinity for target analytes

Sample is incubated with the plastic-bound antibody

If an analyte is present in the sample, it will form a complex with the antibody

Wells are then washed to remove any unbound sample and reagent

A monoclonal antibody is added to the well, which is specific to another area of the antigen

Chromogenic substrate is added to the second antibody

Intensity of the color is proportional to the concentration of the analyte in the sample

Explain how GC/MS works

GC separates components of the mixture

The MS records the sample’s mass spectrum

• Consists of a series of small mass peaks (fragments) that are unique to organic compounds

Most reliable confirmation test for forensic toxicology

Explain how mass spectrometry works

Mass is presented on the x-axis, and intensity of the mass on the y-axis

Molecular ion (M+) peak

Computers are equipped with a library of reference spectra from compounds

What is the molecular ion peak

M+ peak occurs when the molecule is bombarded with electrons, causing one electron to get knocked off the molecule, creating a positive ion

Corresponds to the molecular mass off the molecule

How long do drugs remain in the bloodstream

~24 hours

How long do drugs remain in the urine

~72 hours

How is hair helpful in forensic toxicology

Because hair is nourished by blood flowing to the root, drugs in the blood will diffuse through capillary walls into the base of the hair. Drugs are then permanently trapped in the keratin structure of the hair. Hair grows ~1 cm per month

What is determined from postmortem toxicological information

How the poison entered the body

Whether enough poison was ingested to cause death

Where is the highest concentration of poison usually found

Where it entered the body

What is the ratio of alcohol in blood to alcohol in breath

2,100 to 1

In other words, 1 mL of blood will contain nearly the same amount of alcohol as 2,100 mL of alveolar breath

What reaction produces fire

Oxidation reactions

What is an oxidation reaction

A chemical reaction between a substance and oxygen

What are examples of slow oxidation reactions

Rusting or bleaching

What are examples of fast oxidation reactions

Combustion or fire, where there is a rapid release of heat

What is an example of an extremely fast oxidation

Explosions

What is activation energy

Minimum energy that reactant molecules must possess to react

What factors change the rate of a chemical reaction

Temperature

Concentration of reactants

Presence of a catalyst

How is a flame produced

Fuel produces a flame only when sufficient molecules exist in the gaseous state. Once a liquid reaches its flash point, fuel can be ignited by an outside source of heat

What is flashpoint

The minimum temperature at which a liquid fuel will produce enough vapor to burn

Which is higher, ignition temperature or flash point

Ignition temperature

What is flash point for flammable liquids

<100ºF

What is the flash point for combustible liquids

≥100ºF

What are accelerants

Materials used to start or sustain a fire

Liquid accelerants form flammable or explosive vapors at room temperature

What is pyrolysis

Chemical decomposition of a substance by heat

What is flammable range

Concentration of gaseous fuel that will support combustion

What are the essential ingredients of a fire

Fuel, air, sufficient heat

What is the sequence of events during a fire

Incipient stage

Free-burning stage

Smoldering stage

Describe the incipient stage

Ignition of fire

Gases rise in the room

Oxygen dives to the bottom of the flames

Fire produces a “V” pattern on vertical surfaces

Describe the free-burning stage

Fire consumes more fuel and intensifies

Flames spread upward and outward

A dense layer of smoke and fire gases accumulates near ceiling

At a temperature of 1100ºF, all flues in the room ignite (flashover)

If fire stays confined to the area it originated, its growth depends on the amount of O₂ available

Entire structure becomes engulfed in flames

Describe the smoldering stage

All fuel is consumed, and the fire’s open flames disappear

If oxygen suddenly enters the area, the soot and fire gases can ignite with explosive force, producing a backdraft

What is a hydrocarbon accelerant

Accelerants composed of carbon and hydrogen

Presence of specific hydrocarbons in fire debris may indicate that a certain accelerant was used

What is the point of origin of a fire

Place where the fire started

Typically the site of greatest damage

Usually located at the lowest point of intense burning

Most likely area to discover an accelerant or ignition device

What are burn patterns

Physical marks and char that remain after a fire

What are some types of burn patterns and what can they indicate

Lines or darkened areas record the boundaries between different levels of heat and smoke

Direction the fire traveled can be determined from burn holes in walls or ceilings

Measuring the depth and extent of charring may help estimate the duration of the fire

What does charring on the underside of furniture on the floor indicate

Use of a flammable liqiuid

What is burn pattern geometry

Shapes on the walls or floors may indicate handling of accelerants

What does an hourglass pattern indicate

Pool of burning liqiuid

What does a pour pattern indicate

Burn in the middle of a room

What does a trailed pattern indicate

Burn pattern that resembles a flowing stream; liquid was spread from one location to another

What do melted objects indicate

Melted objects, especially metals, can assist in determining intensity and duration of the heating