Lab Tools of Forensic Scientists

Detection Presumptive tests ◦ Give idea as to what probably is in a sample/what definitely is not in a sample  Ex: chromatography (all types) color tests UV and visible light spectrophotometry/colorimetry Confirmation tests ◦ Definitive/conclusive results  Ex: microcrystalline tests IR spectrophotometry (FT-IR) Mass spectrometry

Color Testing

Thin Layer Chromatography

Microcrystalline testing

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Properties of Light Dual nature- particle and wave behavior Particle nature= “photon” (packet of light energy) Electromagnetic radiation moves in waves

Electromagnetic Spectrum

Dispersion of Light through Prism

How can light help to identify a substance?

The solutions of many compounds have characteristic colors. The intensity of such a color is proportional to the concentration of the compound.

What are Spectroscopy and Spectrophotometry?? Light can either be transmitted or absorbed by dissolved substances Presence & concentration of dissolved substances is analyzed by passing light through the sample Spectroscopes measure electromagnetic emission Spectrophotometers (and colorimeters) measure electromagnetic absorption

What we use in lab: ◦ Vernier Colorimeter

Spectrophotometer/Colorimeter

Beer’s Law The intensity of a ray of monochromatic light decreases exponentially as the concentration of the absorbing medium increases. More dissolved substance = more absorption and less transmittance

Standardization Graph - Standards (solutions of known concentration) of the compound of interest are made, treated, and their absorbance and concentration values are used to create a Standardization Graph. (This is what we will use in the Killer Cup of Coffee Lab)

Chromatography (“analyze by color”) Separates mixture into components ◦ Analyte= substance being analyzed Provides tentative identification of components of a mixture (not a final identification) ◦ Stationary Phase ◦ Moving Phase

Paper Chromatography What you probably did in Geoscience/Biology ◦ Solid phase= paper ◦ Moving phase= solvent (alcohol, water, etc)  Material dissolved in the solvent moves up the paper, leaving bands of color at various points on the paper. Presumptive (“screening”) test

Thin Layer Chromatography Stationary Phase= solid (plate w/silica gel or aluminum oxide) Moving phase= liquid (solvent) Most compounds are colorless, so plates are placed under UV light and visualized. Results can give “retention factor”, or R f, values. Presumptive (“screening”) test

Thin Layer Chromatography (Click picture to view video)

Thin Layer Chromatography

Gas Chromatography Used to separate substances based on the affinity of the various components to the mobile (gas) phase or the stationary phase. Produces a “chromatogram” Identifies the individual components based on their retention times. Identifies concentrations of components Often used in tandem with Mass Spectrometer Presumptive (“screening”) test

GC-MS (Click picture to view video-no animation)

Mass Spectrometry 1A small sample is ionized (given a charge by removing an electron). 2The ions are sorted and separated according to their mass and charge. 3The separated ions are then measured, and the results displayed on a chart. (Click picture to view video)

Mass Spectrometry Print out is a chemical “fingerprint” of the substance. “Mass spectrum” Confirmatory (positive identification test)

FT-IR

Tools & Techniques for Separation and Identification of Substances Tool/TechniqueTypes/VariationsDescriptionUseful for/because… Chromatography SpectroscopyFTIR Spectrophotometry/ Colorimetry