Forensic Toxicology VME 6613 Exam With
Complete Solutions
Possibility of Sample Contamination - ANSWER One of the biggest concerns of any
forensic laboratory and the point of attack for many defense attorneys
is identifying a sample as being positive for a particular drug when in fact none is
present.
associated with contamination of the case sample with the drug in question, or failure of
the analytical test to produce an accurate result. - ANSWER False Positive
a less serious error
failing to identify the presence of a drug when it is known to be present in the sample.
associated with the failure of the analytical test and can result in critical data being lost.
- ANSWER False Negative
a substance that is known to react in the same way as a positive sample.
For example, if testing a urine sample for the presence of amphetamine, a urine sample
spiked with a standard solution of amphetamine will suffice as a positive control. -
ANSWER Positive Control
a drug free urine sample. - ANSWER Negative Control
solutions of drugs or chemicals of known concentration - ANSWER Standard Solution
• Weight if in powder form (note if dry weight or wet weight)
,• Amount if in tablet form
• Number of packages
• Nature of the substance
• Color
• Odor (if obvious)
• Condition- wet or dry - ANSWER When samples are acquired for testing the
appearance and features of the substance must be recorded. These features include:
chemical, physical or microbial degradation. - ANSWER Many drugs are not chemically
stable and can be subject to
can result in loss of pure drug by breakdown to another compound
Example: cocaine to the metabolite benzoyleconine). - ANSWER Chemical Degradation
• Changes in the crystal form of a drug
• Aggregation of drug particles in a suspension
• Loss of volatile chemical compounds to the atmosphere and container (alcohol) -
ANSWER Physical Decomposition
Occurs in any sample containing water - ANSWER Microbial contamination
hydrolysis, oxidation or photochemical changes, due to the ubiquitous nature of water,
oxygen and light in our environment. - ANSWER Most of the chemical instability of drugs
can be attributed to
• Pharmaceutical products that possess an ester or an amide bond are particularly
susceptible to hydrolysis
• Esters are usually hydrolyzed by acid or base catalysis
, • Examples of drugs susceptible to hydrolysis include cocaine and procaine - ANSWER
Hydrolysis
Photochemical reactions occur when a molecule absorbs a photon of light energy to
produce an unstable excited state molecule. This extra energy can be lost by several
different mechanisms:
• Fluorescence
• Physical decay (loss of energy in the form of heat)
• Chemical decay (breakdown of the drug)
Ultraviolet light is the most energetic light in the spectrum and can induce chemical
decay. Many steroid drugs are susceptible to photolysis. - ANSWER Photolysis
The rate of a chemical reaction is related to the absolute temperature in Kelvin
(Arrhenius). Rates increase by a factor of 2-3 for every 10°C rise in temperature. The
Arrhenius equation is applicable to solution reactions providing that the temperature
range is between 30-50°C. - ANSWER Temperature
can result in physical or chemical changes. - ANSWER Degradation of drugs in the solid
state (tablets)
• Degradation at the tablet surface
• True solid degradation
The most common situation involves reactions in adsorbed surface moisture resulting in
saturated or concentrated drug solutions. The surface solution phase may result from:
melting of the drug or other component and /or adsorbed moisture from the
atmosphere. - ANSWER Solid-state decomposition can be divided into two types:
Involves no change in the covalent bonds of the drug but may involve changes in the
crystal lattice structure. - ANSWER Physical Decomposition
repeating arrangement of individual molecules (crystal lattice) and a characteristically
Complete Solutions
Possibility of Sample Contamination - ANSWER One of the biggest concerns of any
forensic laboratory and the point of attack for many defense attorneys
is identifying a sample as being positive for a particular drug when in fact none is
present.
associated with contamination of the case sample with the drug in question, or failure of
the analytical test to produce an accurate result. - ANSWER False Positive
a less serious error
failing to identify the presence of a drug when it is known to be present in the sample.
associated with the failure of the analytical test and can result in critical data being lost.
- ANSWER False Negative
a substance that is known to react in the same way as a positive sample.
For example, if testing a urine sample for the presence of amphetamine, a urine sample
spiked with a standard solution of amphetamine will suffice as a positive control. -
ANSWER Positive Control
a drug free urine sample. - ANSWER Negative Control
solutions of drugs or chemicals of known concentration - ANSWER Standard Solution
• Weight if in powder form (note if dry weight or wet weight)
,• Amount if in tablet form
• Number of packages
• Nature of the substance
• Color
• Odor (if obvious)
• Condition- wet or dry - ANSWER When samples are acquired for testing the
appearance and features of the substance must be recorded. These features include:
chemical, physical or microbial degradation. - ANSWER Many drugs are not chemically
stable and can be subject to
can result in loss of pure drug by breakdown to another compound
Example: cocaine to the metabolite benzoyleconine). - ANSWER Chemical Degradation
• Changes in the crystal form of a drug
• Aggregation of drug particles in a suspension
• Loss of volatile chemical compounds to the atmosphere and container (alcohol) -
ANSWER Physical Decomposition
Occurs in any sample containing water - ANSWER Microbial contamination
hydrolysis, oxidation or photochemical changes, due to the ubiquitous nature of water,
oxygen and light in our environment. - ANSWER Most of the chemical instability of drugs
can be attributed to
• Pharmaceutical products that possess an ester or an amide bond are particularly
susceptible to hydrolysis
• Esters are usually hydrolyzed by acid or base catalysis
, • Examples of drugs susceptible to hydrolysis include cocaine and procaine - ANSWER
Hydrolysis
Photochemical reactions occur when a molecule absorbs a photon of light energy to
produce an unstable excited state molecule. This extra energy can be lost by several
different mechanisms:
• Fluorescence
• Physical decay (loss of energy in the form of heat)
• Chemical decay (breakdown of the drug)
Ultraviolet light is the most energetic light in the spectrum and can induce chemical
decay. Many steroid drugs are susceptible to photolysis. - ANSWER Photolysis
The rate of a chemical reaction is related to the absolute temperature in Kelvin
(Arrhenius). Rates increase by a factor of 2-3 for every 10°C rise in temperature. The
Arrhenius equation is applicable to solution reactions providing that the temperature
range is between 30-50°C. - ANSWER Temperature
can result in physical or chemical changes. - ANSWER Degradation of drugs in the solid
state (tablets)
• Degradation at the tablet surface
• True solid degradation
The most common situation involves reactions in adsorbed surface moisture resulting in
saturated or concentrated drug solutions. The surface solution phase may result from:
melting of the drug or other component and /or adsorbed moisture from the
atmosphere. - ANSWER Solid-state decomposition can be divided into two types:
Involves no change in the covalent bonds of the drug but may involve changes in the
crystal lattice structure. - ANSWER Physical Decomposition
repeating arrangement of individual molecules (crystal lattice) and a characteristically
