forensic chem exam 3

what are the two applications of spectroscopy?

1. molecular: organic molecule identification 

2. atomic: element identification

what is the definition of a chromatogram? versus the definition of a chromatograph?

chromatogram: actual graph, output

chromatograph: the instrument

what is the definition of a microscope?

a form of spectroscopy, but no instrument output

what is the definition of spectroscopy?

the interaction of light (or electromagnetic energy) with matter

what is the definition of a spectrum?

a range; output of interaction of light with matter 

what is the definition of spectra?

plural of spectrum (multiple spectra)

what is the difference between spectrometer versus spectrometry?

spectrometer: instrument that measures

spectrometry: the technique itself

what are the two wave properties of light and their definitions?

1. wavelength: distance between 2 crests or troughs 

2. frequency: how fast waves come in a given time  

does a longer distance mean lower of higher frequency?

does faster waves mean less or more energy

lower frequency

more energy

how does light travel?

→ light is a wave: travels in a straight line

→ light travels in a packet of energy: photon; each packet of energy = photon

what are the 3 properties of particles in light?

1. frequency 

2. wavelength 

3. energy 

how does spectroscopy work?

→ stimulated by applying energy in the form of heat, electrical energy, light particles or chemical reaction

→ irradiate with energy: creates different interactions

→ these interactions are: adsorb some energy or scattering of light

→ the energy that is absorbed: if energy matches, the electron will move from the ground state to the excited state

→ there will then be an emission: release of extra energy

which is a scattering technique and which is a adsorption technique: UV VIS, IR Spec and Raman Spec

adsorption technique: UV VIS, IR spec

scattering technique: Raman spec

what is the requirement for something to absorb energy?

for something to absorb energy, it must be able to adsorb the same energy: 2 wavelengths get along with each other 

→ certain functional groups absorb at a certain wavelength 

what is a continuous spectrum? emission spectrum? absorption spectrum?

→ continuous spectrum: spectrum that contains all wavelengths emitted by a hot, dense light source; emits energy with all wavelengths

→ emission spectrum: shows colored lines of light emitted by glowing gas; single spike at the wavelength it was emitted

→ absoprtion spectrum: shows dark lines or gaps in light after the light passes through a gas

what is the difference between molecular spectroscopy, spectroscopy, and chromatography?

→ molecular spectroscopy: gives a fingerprint of a material

→ spectroscopy: identify a material

→ chromatography: separation

what is photoluminiscence?

• species are excited by absorption of a beam in EM radiation and radiant emission then occurs as the excited species returns to the ground state 

• emitted radiation is lower in energy than absorbed radiation 

• phosphorescence is slower than fluorescence due to a relaxation to a metastable triple state  

what are the 2 techniques of emission in terms of photoluminescence?

1. fluorescence: goes away when light is turned off 

2. phosphorescence: slowly fades 

how is fluorescence used in forensic science?

• alternate light sources in crime scenes 

• trace evidence examination 

• document examination 

• fluorescent tags to primers in DNA analysis 

• fluorescence spectroscopy for chemical detection 

• fluorescent tags as markers for substances (some explosives) 

what are the 5 components of a spectrometer?

1. source of radiant energy: where light comes from

2. sample container

3. wavelength detector

4. radiation detector

5. signal processor

how does UV spectroscopy work (diagram terms)

the source is directed to the entrance slit → dispersion device → exit slit (only one wavelength passes through) → sample (usually a cuvette as sample holder) → detector

• the monochromator (one color wavelength) includes the entrance slit, dispersion device, and exit slit

what is the difference between atomic absorption and molecular absorption?

atomic absorption 

→ one or more electrons of the atom is raised to a higher energy level 

→ consists of sharp well-defined lines 

molecular absorption 

→ more complex than atomic spectra due to large number of energy states 

→ total energy due to electronic, vibrational, and rotational energy

what is the process of atomic absorption?

• used for metals

• sample is atomized

• a light source (hollow cathode lamp) emits a light characteristic of the element being tested

• light passes through a vaporized sample: ground state atoms absorbs the light

• amount of light absorbed, from a specific wavelength, is measured

• amount of light absorbed correlates to the concentration of the element in the sample

properties of UV-Vis

• photons of UV and visible light have enough energy to cause transitions between the different electronic energy levels (outer electrons)

• broad bands observed for molecules (Evib and Erot)

  • solution band broadening occurs in non-ideal solutions

• most absorption by organic compounds results from the presence of pi bonds (double or triple bonds; conjugated ring systems)

conjugated ring system → CAN analyze by UV/Vis

no conjugated ring → CANNOT

what are the two types of UV detectors?

1. fixed wavelength: only lets a single wavelength through 

2. diode array detector: shows UV/Vis detector on HPLC range of interest; gives more information 

what is microspectrophotometry?

• used for determining exact color of tiny paint chips

• used to analyze fibers/textiles to compare the exact colors of two fibers

how does a fluorescence detector work?

excited → fluoresce with emission → then detect

the sample in must be a liquid or solution (can therefore be hooked up to an LC)

• excitation and emission wavelengths can be changed

• molecules can be derivatized to be amendable to fluorescence detector

A fluorescence detector works by first exposing a sample to a high-energy light source, which excites some compounds to a higher energy state. As these excited compounds return to their ground state, they emit light at a longer, lower-energy wavelength (fluorescence). The detector then measures the intensity of this emitted light at a specific wavelength to identify and quantify the fluorescent compounds in the sample

what does a fluorescence detector detect?

things that fluoresce:

1. conjugated ring systems

2. polycyclic aromatic hydrocarbons (PAHs)

3. xanthenes

what are the principles of IR?

• Fourier Transform Infrared Spectroscopy (FTIR)

  • FT: mathematical function

  • IR: a type of molecular spectroscopy

• vibrational spectroscopy

• IR regions

  • near: 780-2500 nm (12800-4000 1/cm)

  • mid: 2.5-25 micro meter (4000-400 1/cm)

  • far: 25-1000 micro meter (400-10 1/cm)

  • “fingerprint region” (<1500 1/cm)

why is infrared absorption spec a good way of recognizing functional groups?

molecules absorb infrared light by changing their vibrational energy levels. specific groups of atoms have their own characteristic infrared absorption frequencies. Thus infrared absorption spectroscopy is a good way to recognize functional groups on molecules 

how do molecules move on a molecular level in terms of IR?

symmetrical stretch, anti-symmetrical stretching, scissoring, rocking, wagging, and twisting

how do infrared spectrometers work (diagram)?

a laser beam is reflected off a sample then reflected into a detector 

old way vs new way of FTIR

→ old way

• sample is ground w KBr

• KBr mix is pressed into a thin pellet under high pressure

• pellet is placed into sample holder

• KBr is used because it is transparent to IR light

→ new way

• can analyze solids, liquids, gases using different sample chambers

what are the applications of IR?

• organic analysis 

• structural determination 

• functional group identification 

• isomer differentiation 

• differentiation of salt vs free vase drug forms 

• analysis of paints and historic paintings 

what are the 2 weaknesses of IR?

• must be a pure sample, cannot differentiate mixtures easily

• sample prep is sometimes difficult

what is Raman spectroscopy?

• surface is illuminated by a laser, light then scatters off with a different energy (hitting a covalent bond causes light to change)

• molecules have vibrational frequencies

• incoming light with the same frequency as the wavenumber of the vibration will excite the bond and cause the light to come back with a different energy-a Raman effect which causes Raman scattering

• since the frequencies of light absorbed when a molecule is illuminated are unique to the molecule and types of bonds, detecting these frequencies of light will allow us to figure out which molecules are present in the sample

what is the difference between Raman and Rayleigh scattering?

Rayleigh scattering: incoming and outcoming energy does not change; a surface is hit with a laser of certain wavelength and the same wavelength is then scattered off 

Raman: incoming and outcoming energy does change; laser of a wavelength is hit on the surface and produces a scattering pattern of different wavelengths 

why is Raman good for drug testing?

many materials are “invisible” to Raman, including most plastics, opaque items, and glass. this allows us to test for drugs without removing them from their packaging → ideal for cops to avoid opening packaging

what causes invisibility to Raman spectroscopy?

• if the molecular vibrations do not cuase a significant change in polarizability

• if the molecule does not experience a noticeable shift in its electron distribution when vibrating

• the molecule does not interact strongly enough with the incident light to produce measurable Raman scattering

what works well for Raman spectroscopy?

• organic materials including active pharmaceutical ingredients, organic solvents, polymers, harmful narcotics, and explosives 

• polyatomic inorganics such as (salts) magnesium sulfate, sodium bicarbonate, titanium dioxide, and calcium phosphate 

• molecules containing only single bonds: C-C, C-H, C-O

• highly polar small molecules such as ethanol 

what does not work well for Raman spectroscopy?

• materials with no covalent bonds: purely ionic species (ex: NaCl will have no Raman energy because it is ionic bond → no covalent bond = no vibration)

• highly fluorescent samples including plant based materials 

• black or dark colored samples as the material may completely absorb the laser light 

• any substance with a weak Raman signal within the region being examined 

• most metals and elemental substances 

what is a Thermo Fisher TRUNARC?

drug testing device used to test drugs in their packets

• very user dependent

• will not be able to distinguish a mixture, shows the most detected substance in a mixture only

what is SORS?

spatially offset Raman Spectroscopy

• works through opaque containers

• direct analysis is suboptimal

• laser generates fluorescence similar to a 785 nm Raman system

• i-Raman PRO ST

• specialized laser excitation can overcome opaque containers

• “subtraction” of the container’s spectrum components from other laser component

what is See Through Raman?

STRaman or STRam

• materials like paper bags fluoresce at 785 nm, making SORS useless

• STRaman uses 1064 nm laser excitation source 

what is the difference between laser at zero physical offset and laser with a physical offset?

1. the “laser at zero” geometry favors collecting photons closest to the surface (migrating the least inside the sample) and therefore collecting more inelastic scattering from the top layers

2. the “laser with a physical offset” geometry favors collecting more of the photons migrating through deeper zones of sample collecting more inelastic scattering from the sub surface layers

what is an explosion?

is a rapid release of energy (pressure or shock wave) which is characterized by high temperatures, large volumes of gases, light or sound

what are the three types of explosion?

1. chemical

2. mechanical

3. nuclear or atomic

what are energetic materials and what are the 3 forms of energy release?

a material which can undergo a self-sustaining chemical reaction which rapidly releases a large amount of energy

forms of energy release:

1. light

2. heat

3. sound

what are explosives?

• type of energetic material 

• any material, pure or a mixture, which is capable of exploding by its own energy 

what are the two fragmentation patterns observed from explosions?

→ primary fragmentation: things that break off where the explosion is

→ secondary fragmentation: the blast front hits something and the something breaks off

how are explosives classified based on the rate of reaction?

low

• an explosive in which the chemical reaction through the material proceeds slower than the speed of sound (subsonic)

• deflagrate (deflagration reaction)

high

• an explosive in which the chemical reaction through the material proceeds greater than the speed of sound (supersonic)

• detonate (detonation reaction)

where do the reaction products go in terms of deflagration and detonation reactions?

deflagration: move in opposite directions; some move toward reaction products and some move toward the unreacted explosive

detonation: everything goes in one direction; moves from the detonation products through the shock front and to the unreacted explosive

explosive classification in terms of chemical composition?

→ inorganic 

• pyrotechnic or inorganic propellants 

• composed of inorganic oxidizer and organic fuel

• nitrogen and chlorine based salts 

→ organic 

• most of these explosives share C, N, H, and O in their formula

• nitroaromatic compounds: DNT, TNT

• nitramines: RDX, HMX

• nitrate esters: nitroglycerin, EGDN, PETN

what are improvised explosives?

→ commercial explosives

• legitimately manufactured materials

• devices with intended use and purpose (regulated manufacturer)

→ improvised explosives (home-made explosives)

→ the most common IEs

• urea nitrate, ANFO ammonium nitrate and fuel oil, flash powders, pyrotechnics (oxidizer/fuel)

→ peroxide based IEs:

• TATP, HMTD, liquid explosives

what is the role of a chemist in the analysis of explosives?

role of chemist: identify the bulk explosive used in the device 

what are the types of explosive evidence?

1. device components

2. failed device: bulk explosive

3. trace explosives on post blast debris

what is the challenge in analyzing explosion evidence?

could be contaminated with other stuff, might explode (no destructive techniques), it destroys its own evidence

what kind of presumptive screening can be used for explosive analysis?

thin layer chromatography (TLC)

what are the categories for bulk explosives?

bulk explosives

• categories 1 and 2 (best): IR, GC/MS, EDX, Raman Spectroscopy, XRD, LC/MS

• category 3 (decent): GC, GC-TEA, LC, LC-TEA, IC, CE, TLC, IMS, PLM, SLM

• category 4 (presumptive): burn test, flame test, spot test, and melting point

what are post-blast residues?

• usually only combustion products are left after an explosion

• several of the residues may be naturally found in the environment for inorganic explosives

• post-blast residues of organic explosives usually include nanogram quantities of parent compound and little or no detectable reaction products

what are the categories for trace explosives?

trace explosives 

• categories 1 and 2 (best): IR, GC/MS, EDX, Raman spectroscopy, XRD, LC/MS, IC/MS, XFR

• category 3 (decent): GC, GC-TEA, LC, LC-TEA, IC, CE, TLC, IMS, PLM, SLM

• category 4 (presumptive screening): flame testing, spot testing, and melting point 

what is combustion and what are the forensic investigations that involve combustion?

→ combustion

• oxidative decomposition where oxygen oxidizes fuel

• associated with release of heat and light

→ forensic investigations that involve combustion

• arson

• gunshot residues

• explosives

what are the requirements for combustion?

• fuel and oxidant combine in appropriate quantities 

• source of energy 

• sufficient time for energy source to initiate the reaction; the reaction proceeds by:

  • inititation of free radicals

  • propagation of chain reaction

  • termination of reaction

what are the speeds of combustion from longest to shortest?

flames (fire) < propellants < low explosives < high explosives (shortest time relative to each other)

what are the 4 things required to sustain a fire reaction?

1. fuel

2. heat

3. uninhibited chemical chain reaction

4. oxidizing agent

if you knock one out → you stop the fire

what are fuels and oxidants?

fuels: solid and liquid materials do not burn in their initial phase and must be first converted to the gas phase before ignition of the flammable vapors

oxidants: atmospheric oxygen and chemical oxidizers

what 3 things does every fire have?

1. lower flammability limit: fuel lean 

2. flammable range 

3. upper flammability limit: fuel rich

what is the definition of ignition temperature?

the lowest temperature at which a volatile material will be vaporized into a gas which ignites without the help of any external flame or ignition source

what is the definition of flash point?

the lowest temperature at which a substance vaporizes into a gas, which can be ignited with the introduction of an external source of fire

what are the 3 forms of heat transfer?

1. conduction: fire touching something, the thing gets hot. you touch the thing and get hot. 

2. convection: movement of hot air, heats cold air 

3. radiation: feel the heat of the fire directly through the air 

what is the definition of flashover?

transition phase in the development of a contained fire in which surfaces exposed to the thermal radiation, from fire gases in excess of 600°C, reach ignition temperature more or less simultaneously and fire spreads rapidly through the space

what are the 3 stages of compartment fires?

1. open fire

2. flashover

3. decay

what is arson and why is it a crime? 

→ arson 

• intentional burning of property 

• incendiary 

→ arson is a crime because: 

• loss of life 

• injuries 

• loss of property 

why does a chemist need to know about fire?

• to know what products we are looking for

• set intentionally or not

• experiments could catch fire

• how it cam effect evidence and where evidence is taken from correctly

what is the role of fire fighters (first responders)?

• first on the scene

• suppression of fire

• observe and record key aspects of fire

• overhaul

→ they knock down the fire (put out the flames), they do not look for evidence (they may damage the crime scene)

what is the role of the fire investigator

after the fire is out: 

• determine if this was an accidental or intentional act 

• what caused the fire? 

  • accidental (faulty wiring)

  • natural (lightning)

  • incendiary (burning evidence to cover crime scene)

• collect evidence relevant to cause

• determine origin of fire

what is the difference between porous versus nonporous materials at a fire scene 

→ porous: things an accelerant can seep into; retain accelerants better; burns faster 

• wood, carpet, foam padding, soil, paper, cloth 

• retain accelerants 

• a better choice to sample 

→ nonporous

• plastic, metal, tile/ceramic, glass (all harder to burn)

• retain accelerants poorly 

• not a good choice to sample 

what are the evidence items and collection process for a fire scene?

→ evidence items 

• fire patterns 

• artifacts from fuel

• artifacts from ignition source 

• samples for ignitable liquids (accelerants) 

• any evidence of foul play 

→ collection 

• clean, unused metal cans: paint cans 

• teflon lined cans for collection of wet evidence 

• prevent contamination 

• document with photographs 

what are the control samples used for fire?

• control: a blank for the collection substrate; only want a negative control; a blank we are subtracting out

  • ex: gauze pad, cotton swab

• comparison sample: same substrate as sample; from an area suspected to contain no added ignitable liquid

  • ex: carpet, foam padding

how are accelerants detected in the field?

• Scott Instruments TLV Sniffer 

  •  combustible gas indicator designed to detect PPM concentrations of most types of flammable liquid vapors and gases

  • generally accepted in court and has less of a factor of operator influence

• ATF accelerant detection canines

  • faces challenges in courtroom acceptance and has a potential factor for operator influence

what are the 3 approaches for field analysis of fire?

basic approach

1. visually inspect and photograph the scene 

2. collect, preserve, and transport samples to the lab 

layered approach

1. visually inspect and photograph the scene 

2. pinpoint useful samples with K9 or instruments 

3. collection of sample vapors at scene 

4. collect, preserve, and transport samples to the lab 

advanced approach 

1. visually inspect and photograph the scene 

2. pinpoint useful samples with K9 or instruments

3. SPME/GC/MS field ID of suspect samples 

4. interpret and collect additional samples 

5. collect, preserve, and transport samples to the lab

what are the 3 approaches to lab analysis of fire?

basic approach

1. GC or GC/MS analysis and interpretation 

2. combine results, conclude and testify 

layered approach 

1. GC or GC/MS analysis and interpretation

2. combine results, conclude and testify

advanced approach 

1. GC or GC/MS analysis and interpretation

2. advanced analysis to improve sensitivity and selectivity 

3. combine results, conclude and testify

how is fire debris most popularly analyzed?

• most popular sample preparation:

  • passive headspace concentration with activated charcoal (if concentrated enough, could inject with headspace)

• most popular analytical method:

  • gas chromatography-mass spectrometry

  • adsorbents

  • desorption

→ GC FID and GC TCD can also be used

what is the classification of ignitable liquids?

• petroleum based ignitable liquids 

  • numerous classes of liquids that can be grouped together based on chemical composition

  • each class contains numerous components

• OSAC classification

  • light (C4-C9) ; ex: gasoline

  • medium (C8-C13) ; ex: kerosene

  • heavy (C9-C20+)

what are petroleum products?

• derived from crude oil 

• undergo distillation 

• gasoline formed by additional processes 

  • alkylation

  • isomerization/reforming

  • cracking

• speciality products also formed

• petroleum is not comprised of a single compound, it is a mixture

what is the classification and identification for ILRs? 

• current ASTM classification: 

• the classification of ignitable liquids is based upon the chemical composition and the carbon ranges of known ignitable liquids which may be encountered in forensic fire debris analysis 

  • current classification: 12 classes

  • E1412-19 and E1618-19

how is GC-MS analysis used for ignitable liquid residues?

• classification and identification of ignitable liquid residues:

1. pattern recognition of gas chromatographic data

2. mass spectral features

   1. full spectra

   2. target compound chromatography (want SCAN not SIM mode)

   3. extracted ion profiling

   4. library reports

what are the components of ammunition?

• bullet 

• cartridge case 

• smokeless powder 

• primer: ignites smokeless powder when the gun is fired 

what is the path for a traditional handgun?

trigger pulled → firing pin strikes primer → burst of flame ignites the smokeless powder → powder combustion produces large quantity of gas; rapid increase of temp and pressure → bullet is pushed out the muzzle → “plume” of gas and burnt/unburnt particles is released through all available openings of the firearm

most residue moves forward into a plume

what is GSR and what are the 2 types?

• GSR refers to all materials generated and translated during or immediately after the discharge of a firearm

  • particles, elements, compounds

• two types: inorganic and organic

what is inorganic GSR?

• mainly contained in the primer mixture; formed after vaporization and condensation of heavy metals 

  • lead, antimony, tin, copper, barium

• the weapon itself and cartidge casing can produce some inorganic GSR (from bullet going through: metal on metal) but generally in much smaller proportions

• primer composition has changed over time, with “heavy metal free” primers being less toxic

  • diazole, zinc peroxides, titanium chlorides instead of lead, barium, antimony

  • police depts may use tagging elements to know if the cop fired the gun

what is organic GSR?

• mainly from the smokeless powder 

  • composed of primary explosives, stabilizers, plasticizers, gelatinizers, sensitizers, flash inhibitors

  • reactions between stabilizers and sensitizers may occur during ammunition storage

• unburnt components of smokeless powder can be found after firearm discharge due to incomplete ignition, vaporization, and condensation

• combustion products are also produced during firearm discharge through pyrolysis, pyrosynthesis processes, and/or chemical rxn

• typical components of organic GSR: DPA, EC< DMP, 2NDPA, 4NDPA

what are burn patterns from a firearm caused by?

incomplete combustion of smokeless powder 

what is the difference between entrance and exit wounds from a GSW?

entrance: inside bevels in

exit: bevels out

closer to contact = more unburned powder on skin

what is primary transfer of GSR and how is it influenced?

• primary: from gun directly to hand when fired

  • during and immediately after firearm discharge

  • on hand(s) of shooter

  • can be transferred to clothes and other body parts like upper arms, chest, face, hair

• infleunced by:

  • type of gun

  • side of gun that the casing ejection port is on

  • openings on the gun

  • length of barrel

  • type of ammunition

what is secondary transfer of GSR?

• secondary 

  • no direct contact between firearm/ammunition and the receiving surface

  • handshaking

  • handling a recently discharged firearm

  • organic GSR is not lost to secondary transfer

• rapid loss of GSR in the first few hours after firearm discharge

  • walking, running, handwashing

  • weather conditions like rain, wind

what is the preliminary testing for GSR?

• color testing for nitrate/nitrite 

  • NOT SPECIFIC

• sodium rhodizonate test sticks

  • red/purple = lead

  • reddish brown = barium

what are the two methods of collection of samples for GSR testing?

1. SEM/EDS

2. swab hand with gauze 

how is testing of samples for GSR done with SEM/EDS?

• inorganic by SEM/EDS

  • scanning electron microscopy/energy dispersive xray spectrometry

  • non destructive

  • the sample material is irradiated with elecrons resulting in the emission of x-rays characteristic to the elements present. the energy emissions are translated into spectral peaks of varying intensity, resulting in a spectrum profile, which identifies the different inorganic elements present in the sample.

what is the definition of a narcotic?

1. any of a class of substances that blunt the senses, as opium, morphine, belladonna, marijuana, and alcohol, that in large quantities produce euphoria, stupor, or coma, that when used constantly can cause habituation or addiction, and that are used in medicine to relieve pain, cause sedation, and induce sleep 

2. any controlled substance, whether sedative or stimulant