Drug Identification
Screening tests vs. Confirmation
• Screening- a test that is nonspecific and
preliminary in nature.
• Confirmation- a single test that specifically
identifies a substance
Drug Identification
• Color Tests
• Microcrystalline Tests
• Chromatography
• Spectrophotometry
• Mass Spectrophotometry
Page 255
Color Tests:
•
•
•
Five (5) primary test reagents
Marquis (2% formaldehyde in
sulfuric acid) Turns purple in
presence of opium derivatives
Turns orange-brown when
mixed with amphetamines and
methamphetamines
Dillie-Koppanyi (1% cobalt
acetate in methanol is 1st added
to the suspect material,
followed by 5% isopropylamine
in methanol)
Turns violet-blue in presence of
barbiturates.
Duquenois-Levine (Solution A
a mixture of 2% vanillin and
1% acetaldehyde in ethyl
alcohol; sol. B concentrated
hydrochloric acid; sol C is
chloroform)
Turns purple in the presence of
marijuana.
• Van Urk (1% solution of p-
dimethylaminobenzaldehyde in
10% concentrated hydrochloric
acid and ethyl alcohol)
Turns blue-purple in presence of
LSD.
• Scott Test ( solution A is 2%
cobalt thiocyanate dissolved in
water and glycerine 1:1; solution
B is concentrated hydrochloric
acid; solution C is chloroform)
This is a test for cocaine. Will
turn blue in the presence of
solution A, pink in the presence of
solution B, and back to blue in the
presence of solution C.
Microcrystalline Tests
• Test to identify specific substances by the
color and morphology of the crystals
formed when the substance is mixed with
specific reagents.
What is a crystalline precipitate?
Microcrystalline Tests
• These tests are rapid and often do not
require the isolation of the drug from its
diluents.
• Most color and crystal tests are largely
empirical, that is we do not fully
understand why they produce the results
that they do.
Chromatography
• We know it is used to separate mixtures.
• Qualitative versus Quantitative
Qualitative tells us a substance is a
mixture of heroin and quinine
Quantitative tells us that mixture is
10% heroin and 90% quinine
Chromatography
• The theory of chromatography works due to
•
Henry’s Law. (page 125)
The law states “ When a volatile chemical
compound is dissolved in a liquid and is brought
to equilibrium with the air, there is a fixed ratio
between the concentration of the volatile
compound in air and its concentration in the
liquid, and this ratio remains constant for a
given temperature.
Chromatography : Henry’s Law
• An equivalent way of stating the law is that the solubility of a gas in a liquid
at a particular temperature is proportional to the pressure of that gas above
the liquid. Henry's law has since been shown to apply for a wide range of
dilute solutions, not merely those of gases.
• An everyday example of Henry's law is given by carbonated soft drinks.
Before the bottle or can is opened, the gas above the drink is almost pure
carbon dioxide at a pressure slightly higher than atmospheric pressure. The
drink itself contains dissolved carbon dioxide. When the bottle or can is
opened, some of this gas escapes, giving the characteristic hiss (or "pop" in
the case of a champagne bottle). Because the pressure above the liquid is
now lower, some of the dissolved carbon dioxide comes out of solution as
bubbles. If a glass of the drink is left in the open, the concentration of
carbon dioxide in solution will come into equilibrium with the carbon dioxide
in the air, and the drink will go "flat".
Chromatography
What is it and how does it work?
Types of Chromatography
• Gas Chromatography (GC)
• High Performance Liquid Chromatography
(HPLC)
• Thin-Layer Chromatography (TLC)
Types of Chromatography:
Gas Chromatography
• A gas chromatograph is a chemical analysis instrument
for separating chemicals in a complex sample. A gas
chromatograph uses a flow-through narrow tube known
as the column, through which different chemical
constituents of a sample pass in a gas stream (carrier
gas, mobile phase) at different rates depending on their
various chemical and physical properties and their
interaction with a specific column filling, called the
stationary phase. As the chemicals exit the end of the
column, they are detected and identified electronically.
The function of the stationary phase in the column is to
separate different components, causing each one to exit
the column at a different time (retention time). Other
parameters that can be used to alter the order or time of
retention are the carrier gas flow rate, and the
temperature.
Gas Chromatography
Gas Chromatography
• Look at page 129
Figure 5-6 shows a
chromatogram
• GC is highly sensitive and
can yield quantitative
results. This is seen if
compared with a known
amount of substance
compared with the peaks
of the unknown in the
chromatogram.
Gas Chromatography
• An added extension to GC for forensic scientist is
PYROLYSIS gas chromatography.
This is where solid physical evidence material such as paint
chips, fibers, and plastics which normally can not be
dissolved in a gas can be subjected to very high
temperatures (500-1000’C) so they will decompose into
numerous gaseous products. These can now be ran
through a GC to produce a pyrogram. The complexity of
the pyrogram serves as a “fingerprint”. See figure 5-7
page 131.
High-Performance Liquid
Chromatography (HPLC)
• Liquid is used as the ‘moving’ phase
through the column instead of gas.
• Major advantage is the entire process
takes place at room temperature.
This helps with organic explosives and
drugs that are generally heat sensitive.
LSD is an example of such a drug.
Thin-Layer Chromatography (TLC)
• Is a SHEET chromatography
• Has solid stationary phase and
liquid moving phase.
• If the sample to be analyzed is
solid, it must first be dissolved
in a suitable solvent.
• Once the liquid has moved a
sufficient distance (usually
10cm) the development is
complete.
• Then it must be visualized.
Separation of black ink via TLC
Thin-Layer Chromatography (TLC)
To visualize:
1. Plates can be placed under ultraviolet light
revealing those materials that fluoresce as
bright spots on dark background.
2. The plate can be sprayed with a chemical
reagent that reacts with the separated
substances and causes them to form colored
spots.
Thin-Layer Chromatography (TLC)
Turn to page 133. See figure 5-9 and 5-10
What is a Rf value? Value defined as the distance
traveled by the component divided by the
distance traveled by moving liquid phase.
In fig 5-10 the moving liquid was allowed to move
10 cm and the heroin moved 8 cm. The Rf value
is 8/10 which = .8.
The quinine moved 4 cm. What is the Rf value?
Thin-Layer Chromatography (TLC)
Powerful tool to forensic scientist due to:
• Both rapid and sensitive
• Takes less than 100 micrograms for
analysis
• Minimal costs and space to use
• Numerous samples can be analyzed
simultaneously
Spectrophotometry
• In physics, spectrophotometry is the
quantifiable study of
electromagnetic spectra. It is more
specific than the general term
electromagnetic spectroscopy in that
spectrophotometry deals with visible
light, near-ultraviolet, and nearinfrared. Also, the term does not
cover time-resolved spectroscopic
techniques.
• Spectrophotometry involves the use
of a spectrophotometer. A
spectrophotometer is a photometer
(a device for measuring light
intensity) that can measure intensity
as a function of the color (or more
specifically the wavelength) of light.
Important features of
spectrophotometers are spectral
bandwidth and linear range of
absorption measurement.
Spectrophotometer
Spectrophotometry
•
1.
2.
3.
Three measurement types
Ultraviolet (UV)
Visible
Infrared (IR)
Compare figures 5-16 and 5-17 on page 141
IR provides a much more complex pattern.
Mass Spectrometry
• Combination of gas chromatography and
mass spectrometry (GC/MS).
GC separates the mixture and immediately
sends to spectrometer in combination of a
computer.
Figure 5-18 page 144
Collection / Preservation of drug
evidence.
• Refer to Appendix I starting on page 543.