chemistry 440(l3)[1]
TRANSCRIPT
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Chemistry 440Forensic Science
Types of Illicit Drugs
Analysis of Illicit Drugs
Spot Tests for Drugs
Identification of Drugs by IR spectroscopy
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Qualitative analysis vs. quantitative analysis
Qualitative analysis simply deals with the identification
of the substance under consideration where as aquantitative analysis of the substance should provide the
actual percentage composition of the various
compounds that make up the substance.Drug Analysis-Spot Tests (Experiment 20), Lab
Manual pp 175-183,
Identification of Drugs by IR (Experiment 21)Identification of Drugs by GCMS (in-House)
Experiment : Salicylates in Blood Stream by Visible
Spectroscopy (Experiment 22, Part A and B)
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Addiction
Physical vs. Psychological addiction
Physical
causes withdrawl symptoms Alcohol, Narcotics, Depressants
Psychological addiction
Dopamine release Cocaine, PCP
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Classification of Drugs
Opiates/Narcotics
Reduce sensation sleep like state
morphine, heroin, codeine, fentanyl
Both physically and psychologically addictive
Stimulants
Stimulate sympathetic nervous system
high energy, euphoria
amphetamines, cocaine, nicotine
Psychologically addictive
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Classification of Drugs
Hallucinogens Alters perceptions, illusions
LSD (acid), PCP(angel dust), MDMA (Ecstacy),Mescaline (peyote cactus), Marijuana (THC),hallucinagenic mushrooms (psilocybin)
Most neither physical or psychological dependence
Depressants Depress CNS, drowsiness, slowed response
Barbiturates(Phenobarbital), Ethanol
Benzodiazepines (tricyclic anitdepressants) Valium(diazepam),Xanax(alprazolam)
Physically and psychologically addictive
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Analysis Sequence
Observations- Rock like, powdered, wet
Screening Test (Spot tests)- Used to categorize specimens to determine type of
substance present and to determine the bestprocedure to use for confirmation, color tests,microcrystalline tests
Chromatography (mixtures) (GC-MS)
Thin Layer Gas chromatography Mass spectrometry
Liquid chromatography Mass spectrometry (Dr.Huang)
Infrared Spectroscopy (pure) (IR experiment)
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Qualitative Analysis of Drugs
The chemistry section of a forensic laboratory
focuses on but not limited to the identification of
illegal drugs. This unit of the forensic laboratory
may also be asked to chemically identify arson
evidences, explosive analysis, blood alcohol
determination etc.
Spot Tests: Chemical analysis of illicit drugs
begin with a presumptive test more commonly
known as a spot test.
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Color tests
The suspected substance is treated with a particular
reagent that produces a color change indicating the
possible presence of a particular substance.
A positive coloration from a color test will always be
followed by additional tests to confirm the identity of the
substance. (IR, GC-MS etc)
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Color Test ReagentsMarquis Reagent: 2% formaldehyde in sulfuric
Acid (coloration with opiates and amphetamines)
Dillie Koppanyi Reagent: 1% Co(acetate)2 in
methanol followed by isopropyl amine.
(barbiturates)
Duquenois Levine Reagent: Soln. A: 2% vanillin
+ 1% acetaldehyde in ethanol, Soln. B: Conc. HCl
(marijuana)
Van Urk Reagent: 1% solution of p-
dimethylaminobenzladehyde in 10% con. HCl (LSD)
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Color Tests
Scott Test: 2% Co(SCN)2 in water followed by
SnCl2. (cocaine, procaine etc)
Meckes Reagent: Selenous acid
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Selecting an Analytical Technique
Considerations:
Organic v. Inorganic Chemicals
(anabundance of organic compounds areanalyzed as evidences)
Quantitative v. Qualitative
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Spectroscopy and ChromatographySpectroscopy (Spectrophotometry): Results
obtained from the interaction of matter with
electromagnetic radiation.
Infrared spectroscopy and UV-Vis
Spectrophotometry. (require pure material)
Chromatograpahy: Separation technique based on.
GC-MS: Simultaneous separation and analysis (can beconsidered as a qualitative and quantitative technique.
Most evidences collected will need purification
(Chromatography)
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Controlled Substances: Introduction to
Classification of Drugs
-A "collection" of organic compounds, the use of which
is regulated by the government.
It is often the case that a forensic chemist will be askedto qualitatively and quantitatively estimate the presence
and percentage composition of these substances in the
evidence collected near a drug related crime scene.
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Comprehensive Drug Abuse Prevention and
Control Act
In 1970 congress passed Public Law 91-513,
the Comprehensive Drug Abuse Prevention and
Control Act or more commonly known as the
Controlled Substance Act. Prior to the enactment
of this law, the nation had several patched-
together pieces of drug legislation which were
either repealed or superseded by the controlled
substance act.
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Drug-Free America Act
In 1986, the congress passed the Drug-Free
America Act (Public Law 99-570) which supersede
much of the 1970 Controlled Substance Act and
include greatly expanded penalties for the sale ,
manufacturing, possession, trafficking and
use(abuse) of the controlled substances.
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Designer Drugs
A term introduced in the 1986 legislation
anticipating the synthesis of future
analogs/modifications of controlledsubstances so that these new derivatives
become controlled substances even before
they are synthesized.
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Schedule I Drugs
High potency for abuse and no currently accepted
and approved medical use.
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Adrenaline and Noradrenaline
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Amphetamines
Stimulants
Produce intense euphoria
Many structural analogs of amphetamine havesubstantial medical benefits and are thus
present as active ingredients in prescription
medicines. (analytical methods must be very
specific)
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Morphine Based
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Serotonin Type
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Schedule II drugs
High potency for abuse but have currently
accepted and approved medical use with orwithout severe restrictions. Their abuse will
lead to severe physiological and physical
dependence.Opium, Cocaine, codeine, demerol, ritalin,
morphine, some barbiturates
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Metabolites of Cocaine
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Schedule III Drugs
Lower potency for abuse but have currently accepted
and approved medical use with or without sever
restrictions. Their abuse may lead to moderate or low
physical dependence.
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Thin Layer Chromatography
An example of solid liquid chromatography
Common adsorbents
Reverse Phase TLC
Visualization of spots: Visible colored spots, UV, iodine,
reagent sprays etc.
Comparison v. identification
Advantages of the method: Easily performed,
inexpensive, only microgram quantities of substance
required, etc
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Electrophoresis
Movement of charged molecules in presence of a
electric field gradient. (a coming attraction)
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Drugs to be tested
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Acknowledgment
The next several PowerPoint slides thatdescribe the theory and practice of IR
spectroscopy is an instructional
accompaniment to
Organic Chemistry, 5th Edition
L. G. Wade, Jr.
and was obtained from the following source
http://faculty.smu.edu/ebiehl/Wade12.ppt.
http://faculty.smu.edu/ebiehl/Wade12.ppthttp://faculty.smu.edu/ebiehl/Wade12.ppt -
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Introduction to IR
Spectroscopy is an analytical technique
which helps determine structure.
It destroys little or no sample.
The amount of light absorbed by the
sample is measured as wavelength is
varied.
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Types of Spectroscopy
Infrared (IR) spectroscopy measures the bond
vibration frequencies in a molecule and is used
to determine the functional group.
Mass spectrometry (MS) fragments the moleculeand measures the masses.
Nuclear magnetic resonance (NMR)
spectroscopy detects signals from hydrogen
atoms and can be used to distinguish isomers.
Ultraviolet (UV) spectroscopy uses electron
transitions to determine bonding patterns. =>
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Electromagnetic Spectrum
Examples: X rays, microwaves, radio
waves, visible light, IR, and UV.
Frequency and wavelength are inversely
proportional.
c= , where cis the speed of light.
Energy per photon = h
, where h isPlancks constant. =>
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The Spectrum and Molecular Effects
=>
=>
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The IR Region Just below red in the visible region.
Wavelengths usually 2.5-25 m.
More common units are wavenumbers, orcm-1, the reciprocal of the wavelength in
centimeters.
Wavenumbers are proportional tofrequency and energy. =>
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Molecular Vibrations
Covalent bonds vibrate at only certain
allowable frequencies.
=>
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Stretching Frequencies
Frequency decreases with increasingatomic weight.
Frequency increases with increasing
bond energy. =>
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Vibrational Modes
Nonlinear molecule with n atoms usually has
3n - 6 fundamental vibrational modes.
=>
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Fingerprint of Molecule
Whole-molecule vibrations and bending
vibrations are also quantitized.
No two molecules will give exactly thesame IR spectrum (except enantiomers).
Simple stretching: 1600-3500 cm-1.
Complex vibrations: 600-1400 cm-1,called the fingerprint region.
=>
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IR-Active and Inactive
A polar bond is usually IR-active.
A nonpolar bond in a symmetrical
molecule will absorb weakly or not atall.
=>
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An Infrared Spectrometer
=>
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Carbon-Carbon
Bond Stretching Stronger bonds absorb at higher
frequencies:
C-C 1200 cm
-1
C=C 1660 cm-1
CC 2200 cm-1 (weak or absent if internal)
Conjugation lowers the frequency: isolated C=C 1640-1680 cm-1
conjugated C=C 1620-1640 cm-1
aromatic C=C approx. 1600 cm-1 =>
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Carbon-Hydrogen Stretching
Bonds with more s character absorb at a
higher frequency.
sp3 C-H, just below 3000 cm-1 (to the right)
sp2 C-H, just above 3000 cm-1 (to the left)
sp C-H, at 3300 cm-1
=>
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An Alkane IR Spectrum
=>
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An Alkene IR Spectrum
=>
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An Alkyne IR Spectrum
=>
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O-H and N-H Stretching
Both of these occur around 3300 cm-1, but
they look different.
Alcohol O-H, broad with rounded tip.
Secondary amine (R2NH), broad with one
sharp spike.
Primary amine (RNH2), broad with two sharp
spikes. No signal for a tertiary amine (R3N) =>
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An Alcohol IR
Spectrum
=>
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An Amine
IR Spectrum
=>
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Carbonyl Stretching
The C=O bond of simple ketones,
aldehydes, and carboxylic acids absorb
around 1710 cm-1. Usually, its the strongest IR signal.
Carboxylic acids will have O-H also.
Aldehydes have two C-H signals around2700 and 2800 cm-1.
=>
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A Ketone
IR Spectrum
=>
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An Aldehyde
IR Spectrum
=>
O H St t h f
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O-H Stretch of a
Carboxylic AcidThis O-H absorbs broadly, 2500-3500 cm-1,
due to strong hydrogen bonding.
=>
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Variations in
C=O Absorption Conjugation of C=O with C=C lowers thestretching frequency to ~1680 cm-1.
The C=O group of an amide absorbs at aneven lower frequency, 1640-1680 cm-1.
The C=O of an ester absorbs at a higher
frequency, ~1730-1740 cm
-1
. Carbonyl groups in small rings (5 Cs or
less) absorb at an even higher frequency.=>
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An Amide
IR Spectrum
=>
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Carbon - Nitrogen
Stretching C - N absorbs around 1200 cm-1.
C = N absorbs around 1660 cm-1 and is
much stronger than the C = Cabsorption in the same region.
C N absorbs strongly just above 2200
cm-1. The alkyne C C signal is muchweaker and is just below2200 cm-1 .
=>
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A Nitrile
IR Spectrum
=>
S f IR
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Summary of IR
Absorptions
=>=>
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Strengths and Limitations
IR alone cannot determine a structure.
Some signals may be ambiguous.
The functional group is usually indicated. The absence of a signal is definite proof
that the functional group is absent.
Correspondence with a known samplesIR spectrum confirms the identity of the
compound. =>
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Recording IR spectra
Neat: (the sample is placed directly in the path of
the IR beam, good for liquids and gases).
KBr pellet: (The solid sample is pressed into athin pellet with KBr and that pellet is placed in
the path of the IR beam)
Solution: The sample is dissolved in a solvent and the
IR spectrum of the solution is recorded)