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8/2/2019 Forensic Chem HA

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Instrumental Analysis andForensic Chemistry

Hossein [email protected]

1- Quantitative Chemical Analysis (6th Ed.)

Daniel C. Harris

2- Fundamentals of Analytical Chemistry (7th Ed.)Skoog, West and Holler

3- Principles of Instrumental Analysis, (5th Ed.)Skoog, Holler, Nieman


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The Chemical AnalysisTwo general areas of analysis: Qualitative analysis attempting to

identify whatmaterials are present ina sample.

Quantitative analysis determining

how much of a material is present in asample.


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Types of Analysis Complete analysis - The goal is to

determine the amount of eachcomponent in a sample.

Partial analysis -The goal is todetermine the amount of one or a

limited number of components withoutregard to total composition.

Cocaine in a sample.

Alcohol level in blood

Presence of lead in a sample


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Steps in aChemical Analysis

Skoog & West


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Methods of Analysis

Gravimetry - Methods based on measuredweight.

Titrimetry - Methods based on a measuredvolume.

Electrochemical - Approaches that rely onmeasurement of potential, current,resistance, charge,

Spectral Methods - Interaction of an analytewith Electro-Magnetic (EM) radiation.

Chromatography - Separation of a materialdue to its interaction with two differentphases.

Chemometrics - The statistical treatment ofdata


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Light

Detector

SampleWavelength

Selector

Light

Source

Wavelength

Selector

AbsorptionEmissionFluorescence

Spectroscopy


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Spectroscopy IR spectrum IS CONCLUSIVE

IR can specifically identify a substance

IR is a definitive identification technique

Measures a fingerprint of the particular

dug

Disadvantage

The drug must be pure for a definitive

match

May have to perform purification steps


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PhenobarbitoneSeizure control

A person with phenobarbital overdose show a marked decreasein electrical activity, to the point of mimicking brain death.


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Caffeine


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Hair analysis overcomes drug testingproblems associated with urinalysis.

Contamination of the exterior surface of thehair = false positive

IR microscopy examines the interior of thehair and differentiate contamination from

drugs absorbed into the hair from ingestion. Microtom the hair, cross-sectional or lateral,

with spatial resolution of 10 m. 3D IR imaging is possible with Fourier

transform (FT-IR) microscopy

InfraRed (IR) Microscopy


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Molecular Fluorescence

Optical emissionfrom molecules thathave been excited to

higher energy levelsby absorption ofelectromagneticradiation.

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From a German stamp


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Hair Elemental Analysis

Issac Newton HgNapoleon AsBeethoven PbKing Charles II Hg

1- R. Passwater, and E. Cranton, Trace Elements, HairAnalysis and Nutrition, Keats Pub, 1983, p 2722- Atomic Absorption Spectrometry in OccupationalAnd Environmental Health Practice, Vol. 1, D.L. TsallevAnd Z.K. Zaprianov


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Atomic SpectroscopyAtomization is by far the

most critical step inatomic spectroscopy.

Atomic Absorption

Atomic Emission

Atomic Fluorescence


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Gas flow rate = Burning velocityFlashback


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Flame Atomization


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Atomic spectra: predominantly resonance

lines

The higher the atomic number, the more

complicated is the spectra:

Li (30 Lines), Cs (645), Mg (173),Ca (662), Ba (472), Cr (2277),

Fe (4757),Ce (5755), ..

Resolution of the mono-chromator is very

important


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Energy Level Diagram


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Hollow Cathode Lamps

Tungsten anode Cylindrical cathode - made of the element of

interest Sealed glass tube - Ar or Ne at 1-5 torr 300 V, 5-15 mAmps


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Schematic of Instruments


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Sample Preparation

For flame AAS, sample must be in

solution

hot mineral acids

oxidation (wet ashing)

combustion

fusion with with boric oxide sodiumcarbonate

For GFAAS, sample can be solid, but

calibration can be difficult


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How to Introduce the Sample? Solutions

Pneumatic nebulization

Ultrasound nebulization

Electrothermal vaporization

Hydride generation

Solids Electrothermal vaporization

Direct insertion

Laser ablation

Spark or arc ablation

Glow discharge sputtering


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Properties of Flames


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Electrothermal Atomizers

Graphite furnace atomic absorption spectrometry (GFAAS) isalso known as electrothermal (ETAAS).

An ideal graphite furnace:

A constant temperature in time and space during the intervalin which free atoms are produced

Quantitative atom formation regardless of the samplecomposition

Separate control of the volatilization and atomizationprocesses

High sensitivity and good detection limits

A minimum of spectral interferences


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Temp. Programming for GFAA


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Separation Techniques Extraction Distillation Electrophoresis

Capillary Electrophoresis

Chromatography

Thin Layer Chromatography (TLC) Gas Chromatography (GC) High Pressure Liquid Chromatography

(HPLC)


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Distillation


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Thin Layer Chromatography (TLC)


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What is the composition of Unknown From Case

The drug works directlyon the brain and spinalcord by interfering withnormal neurotransmission


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Capillary Electrophoresis


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Ephedrine *does* increase your heart rate and constrict blood vessels.If you are careless, you *can* have a heart attack and/or a stroke.


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Zones of sampling for gunshot residues: (A) web and (B) palm


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Faber-Casellfine Metal

point

MicroFasion

Roller

Pilot PreciseV5 Extra

fine point

TomboRollpen

SanfordUniballVisionmicro

SanfordUniballfine


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Ion MobilitySpectrometer


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Gas Chromatography (GC)

In GC, gaseous analyte is transportedthrough a column by a gaseous mobilephase (carrier gas).

Carrier gas is usually He, N2 or H2.

Stationary phase is usually a nonvolatile

liquid, but sometimes a solid.

Analyte can be either a gas or volatileliquid.


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Columns

15 100 meters long


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Usage

Qualitative analysis

Mass spectrometer

IR spectrometer

Compare retention times

Quantitative analysis

The area under a chromatographic peak isproportional to the quantity of thatcomponent.

For very narrow peaks, peak height can besubstituted for area.


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Flame Ionization Detectors

Eluate is burned in H2 and air.

CH radicals which react with O radicals toproduce CHO+ and electrons.

CH + O CHO+ + e-

Only about 1 in 105 carbon atoms produce

an ion, but ion production is strictlyproportional to the number of carbon atomsentering the flame.

Electrons flow from the anode to the cathode,where they neutralize CHO+ in the flame.

This current is the detector signal.


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Diagram of a Mass

Spectrometer


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GC separation of Gasoline (0.1 uL)components (Fossil Fuels)

GC separation of 0.05 uLof steam distilled wood turpentine,a naturally occurring backgroundfound in many wood samples.

Arson: A wide range of low boiling point components present in standard accelerants


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Most compounds are not sufficiently

volatile for GC analysis.

HPLC uses high pressure to force

solvent through closed columns

containing very fine particles that givehigh-resolution separations.

Smaller particles give more

theoretical plates.

High-Performance Liquid Chromatography

(HPLC)


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Typical equipment for HPLC


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The Column

The stationary phase is usuallyhighly pure, spherical,microporous particles of silicathat are permeable to solvent

and have a high surface area


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The Elution Process

Elution occurs whensolvent displaces solutefrom the stationary phase

Solvent molecules

compete with

solute moleculesfor sites on the

stationary phase.

The more polar the solvent, thegreater its eluent strength, andsolutes will be more rapidly eluted

from the column.


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Detection of a drug and its glucuronide

metabolite(s) is great important in interpretiveforensic and clinical toxicology.Metabolite/drug ratios provide informationabout route, dose and time of exposure.In instances where the parent drug isbiotransformedquickly, the detection of

metabolites allows for the identification ofparent drugs.


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