Transcript 6.1 Notes - Trimble County Schools

Chapter 6
Inorganic Analysis
6.1 Notes
Pg. 150-162
Objectives
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Describe the usefulness of trace
elements for forensic comparison of
various types of physical evidence
Distinguish continuous and line
emission spectra
Understand the parts of a simple
emission spectrograph
Organic vs. Inorganic
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¾ of the weight of the Earth’s crust is
composed of only Oxygen and Silicon
10 elements make up approximately
99% of the Earth’s crust
Carbon is less than 0.1 % of the earth’s
crust
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Therefore you are going to find non-carbon
items at crime scenes
Inorganic
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Non-carbon containing substances
In the lab examiners must compare
pieces of physical evidence for trace
elements which provide markers that
may establish the source of a material
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Read pages 152-154
JFK assassination
Emission Spectrum
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Display of colors resulting from light
passing through a prism
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Separated into its component colors or
frequencies
Continuous spectrum = where all colors
merge or blend into one another to
form a continuous band
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Not all light sources produce a spectrum
but instead produce a series of colored
lines mingled with series of dark bands.
Each line represents a definite
wavelength or frequency of light called
a line spectrum (page 155).
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must be in vapor state
“fingerprint” of element
Very practical method of identification
Emission spectrograph
Instrument used to obtain and record
the line spectra of elements
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Vaporizes and excites atoms so they emit
light
Separates light into frequencies
Records resultant spectrum
Carbon arc
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Method of exciting atoms
2 carbon electrodes
Direct current arc is passed
Arc produces sufficient amount of heat
to vaporize & excite
Inductively Coupled
Plasma (ICP)
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Excitation of atoms occurs by placing
sample in hot plasma torch
ICP used to identify and characterize
mutilated bullets and glass fragments
Atomic Absorption
Spectrophotometer
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Technique for the selective absorption
of light by atoms
Most useful application in providing an
accurate determination of an element’s
concentration in a sample
Sufficiently sensitive in detecting and
quantitating elements that are present
at trace levels