Quiz 2 - New Perspectives in Forensics Science

Lectures 3 & 4

What is the definition of radiation?

The emission or transmission of energy in the form of waves through space or through a material medium

What does spectroscopy involve?

Involves the analysis of electromagnetic radiation absorbed, emitted or scattered by molecules or atoms as they undergo transitions between energy levels

What is IR spectroscopy?

Refers to the analysis of the interaction of a molecule with infrared light

What is molecular spectroscopy?

Involves rotational, vibrational and electronic transitions

What can molecular spectroscopy be used for?

Characterize specimens

What forms of molecular spectroscopy can be used for forensic contexts?

IR, Raman, UV-Vis, fluorescence, and NMR

What are the elements of IR spectroscopy?

• Uses IR

• Measures transmittance/absorbance of IR light through a sample

• Creates molecular fingerprint

• Identify chemicals

• Uses databases to compare unknowns

What is a molecular fingerprint?

Unique spectrum of a molecule

What type of plot is generated from IR?

Spectra plots IR absorbance/transmittance % vs wavelength or frequency

What does the energy band on an IR spectra refer to?

Corresponds to the frequency of the vibration of a part of a molecule

Which molecules are considered to be IR active?

Most molecules except for several homonuclear diatomic molecules

Why is IR spectroscopy most useful?

Capable to analyze all gas, liquid and solid samples

What are the most common IR radiation sources used in IR spectroscopy?

Inert solids that are heated electrically

What is a monochromator?

A device used to disperse or separate a broad spectrum of IR radiation into individual narrow IR frequencies

What are the two categories of IR imaging?

Passive and active

What is passive IR imaging?

No external energy source is used

What is active IR imaging?

External heating or cooling is required

What can IR spectroscopy be used to identify in forensics?

PMI, latent prints, blood stains, fingerprints, tattoos, differentiation of gunshot residues`

What does FTIR stand for?

Fourier Transform Infrared

What does FTIR spectroscopy measure? How does it work?

Absorbance/transmittance of light through the sample using many frequencies from a beam

• Separates components to detect and identify

• Can identify isomers with identical masses

• Analyze microsamples

What are the main applications for FTIR in forensics?

• Identify unknown substances

• Composition of mixtures

• Body fluids

• Quality control

• Latent fingerprints

• Fibers, hairs, drugs, polymers, paint, explosives, documents

What does SWGDRUG stand for?

Scientific Working Group for the Analysis of Seized Drugs

What is the difference between qualitative and quantitative analysis via spectroscopy?

Qualitative = Establish identity of sample
Quantitative = Estimate concentration of analyte in the sample

How does Raman spectroscopy?

Spectra is constructed when monochromatic radiation scatters in all directions after its interaction with sample molecules (inelastic scattering and collisions)

What is Rayleigh scattering?

When the incident light frequency of the incident light is equal to the scattered light the scattering

What is Raman scattering or Inelastic scattering?

When the incident light frequency is different from the scattered light the scattering

What is a Stokes line?

Occurs when the frequency of incident radiation is higher than frequency of scattered radiation

What is an Anti-Stokes line?

When the frequency of incident radiation is lower than frequency of scattered radiation

How is scattered radiation often measured?

Usually measured at right angle to incident radiation

Which band is more intense? Stokes or Anti-Stokes? Why?

Stokes is more intense because it involves transitions from lower to higher energy vibrational levels

How are Anti-Stokes bands measured?

Fluorescing samples because fluorescence causes interference with Stokes bands

What does Raman scattering depend on?

Wavelength of incident radiation

What are the elements of Raman spectrometer?

1. Laser

2. Lenses (Focus and collect scattered light)

3. Filters (Purify)

4. Prism (Split light)

5. Detector

6. Computer

What can Raman spectroscopy produce?

Spectra from solid, liquid, and gas. Can be used for mixed samples

Why are gases more difficult to detect with Raman?

Due to low concentrations

Why does Raman spectroscopy have low sensitivity?

Due to weak Raman scattering is the major problem associated with this technique

What does Raman spectroscopy measure qualitatively and quantitatively?

Qualitative = Frequency of scattered radiations

Quantitative = Intensity of scattered radiations

Is Raman more precise than IR?

Yes

What are the areas in Raman proportional to?

Sample concentration

What are the forensic applications of Raman?

Ink analysis, drug identification, explosives, and trace evidence

What are the advances of Raman for body fluids?

Non-destructive, no sample preparation required, done in-situ

How is Raman used for drug detection?

Used as a rapid, nondestructive, screening method for the presence of methamphetamine encountered in clandestine laboratory liquid samples

Why is Raman used to detect medicine contaminants?

Because it is sensitive to slight differences in chemical structure