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Chapter 6
Inorganic Analysis
6.1 Notes
Pg. 150-162
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
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
Therefore you are going to find non-carbon
items at crime scenes
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
Read pages 152-154
JFK assassination
Emission Spectrum
Display of colors resulting from light
passing through a prism
Separated into its component colors or
Continuous spectrum = where all colors
merge or blend into one another to
form a continuous band
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).
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
Vaporizes and excites atoms so they emit
Separates light into frequencies
Records resultant spectrum
Carbon arc
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)
Excitation of atoms occurs by placing
sample in hot plasma torch
ICP used to identify and characterize
mutilated bullets and glass fragments
Atomic Absorption
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