Transcript Forensic Science Documentation

Chromatography is a method
of physically separating
mixtures of gases, liquids, or
dissolved substances.
Chromatography can be used to
identify drugs, poisons and many
other substances.
Separation is determined by the
molecular size and/or charge
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All forms of chromatography involve 2 phases
 The Two Phases
1. stationary (absorbent) phase
the material on which the separation takes place
2. mobile phase - the solvent transports the
sample
Types of Chromatography - 5 of them
1
Gas Chromatography
-
Gas Chromatography
a gas separates the components
they are then ionized and an electrical signal is
recorded
mobile phase - carrier gas
stationary phase
- thin film of liquid
2
HPLC
High Performance Liquid Chromatography
(HPLC)
- done at room temp. - advantageous for
chemicals that are heat sensitive or volatile example LSD
- a liquid (mobile phase) is pumped through a
column containing fine particles (stationary
phase)
3
TLC
Thin - Layer Chromatography (TLC)
-A plate is coated with a granular gel - usually
silica gel or aluminum oxide (stationary phase)
- the substance to be separated is carried up the
plate by capillary action - the substance with most
affinity for the plate will rise the farthest.
4. Paper chromatography
Same as TLC but paper
is used as stationary phase
4
Electrophoresis
Electrophoresis
- Similar to TLC but the substance is separated
through a gel by electric current
- Due to different size and charge substances will
move across the plase at different speeds.
5
Paper Chromatography of Ink
Two samples of black
ink from two different
manufacturers have
been characterized
using paper
chromatography.
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Retention Factor (Rf)
 A number that
represents how far a
compound travels in a
particular solvent
 It is determined by
measuring the distance
the compound traveled
and dividing it by the
distance the solvent
traveled.
Solve for Rf
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