FOR10002 Lecture Notes - Lecture 5: Forensic Science, Swinburne University Of Technology, Analyte

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FORENSIC SCIENCE - FOR10002
WEEK 5
MODERN ANALYTICAL
TECHNIQUES
Examination of Trace Evidence!
Physical evidence has many forms !
Type of crime – theft, fraud, arson, murder, etc !
Location – indoors, outdoors, vehicles, etc !
Forensic scientist needs to do three tasks !
Identification of possible evidence !
Classification – may involve presumptive testing !
Individualisation – unique source or composition !
Chemical analysis can provide detailed information !
Qualitative and Quantitative analysis !
Comparative analysis with authentic specimens!
Chemistry!
Chemistry is the study of matter and the changes it undergoes !
Matter is anything that occupies space and has mass !
A substance is a form of matter that has a distinct composition and properties !
An element is a substance that contains all the same type of atoms – gold, oxygen, carbon, etc
!
ATOM
An atom is the basic building block of matter !
Each element contains a dierent type of
atom !
All atoms are made from basic subatomic
particles!
MOLECULES
A molecule is a specific combination of
atoms arranged in a particular geometry !
e.g. — Water contains two hydrogen
atoms for every oxygen atom!
FORENSIC CHEMISTRY
Forensic Chemistry is the application of
Analytical Chemistry to answer questions of
a legal nature !
Analytical Chemistry focuses on the development of new methods and the improvement of
existing methods for measuring the characteristics of chemical systems !
Improvements include being able to measure !
-smaller samples !
-more complex samples !
-in a shorter time scale !
-lower amount!
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Analytic Chemistry
“Classical” methods are based on knowledge of chemical reactions !
Invention of the transistor !
“Modern” or “Instrumental” methods are based on detecting responses due to changes in light,
heat, magnetic fields, etc!
Types of Analysis!
Qualitative: obtain information about the identity of substances (elements, compounds,…)
present in a sample !
Quantitative: estimate how much of one, some or most of the substances that are present in a
sample !
The sample may be a solid, liquid, gas or mixture and its state and stability can also be
important factors !
In Forensic Analysis it is often the trace components that enable individualisation !
-The impurities in glass, the ‘cutting agents’ in drugs, etc!
The Sample!
A sample can have many substances, if they are the target of the analysis then they are called
analytes !
All the other combined substances are called the matrix !
The goal of an analysis is to selectively measure an
analyte in the presence (or absence) of the matrix!
Qualitative Analysis!
A specific test responds to only one substance being
measured in the presence of others !
A selective test exhibits preference for one substance
being measured but also responds to other
substances !
Few analyses are specific but this can be improved by
careful sample preparation and measurement !
-separating the dierent substances !
-modifying specific parts of the analyte !
-tuning the detection for a specific property of the analyte!
Qualitative Colour Tests!
Chemical reactions are used as presumptive or colou`r tests !
-Quick field tests applied at the crime scene !
-Can be used to classify illicit substances (toxicology) !
The Marquis reagent turns purple in the presence of heroin, morphine and most opium
derivatives !
-It also become orange-brown when mixed with amphetamines and methamphetamine!
Quantitative Analysis!
A quantitative analysis requires knowledge of the identity of substances in a sample obtained
either from the history of the sample or from a qualitative analysis !
This helps when choosing the appropriate analysis method!
Qualitative tests are usually faster than quantitative tests because quantitative testing requires
additional comparisons with known amounts of the pure target substance !
These substances are known as standards !
The goal is the measurement of concentration !
Proportion of the sample that contains a substance !
BAC measures %weight per volume of ethanol in blood!
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Document Summary

Physical evidence has many forms: type of crime theft, fraud, arson, murder, etc, location indoors, outdoors, vehicles, etc. Forensic scientist needs to do three tasks: identi cation of possible evidence, classi cation may involve presumptive testing, individualisation unique source or composition. Chemical analysis can provide detailed information: qualitative and quantitative analysis, comparative analysis with authentic specimens. An atom is the basic building block of matter: each element contains a di erent type of atom, all atoms are made from basic subatomic particles. A molecule is a speci c combination of atoms arranged in a particular geometry: e. g. water contains two hydrogen atoms for every oxygen atom. Analytical chemistry to answer questions of a legal nature. Analytical chemistry focuses on the development of new methods and the improvement of existing methods for measuring the characteristics of chemical systems: improvements include being able to measure.

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