Infrared
Spectroscopy
By Jocelyn, Amy & Sandip
Theory
• Spectroscopy: The study of molecules, using light wavelengths, we can
see the absorption of light into different chemicals.
• Infrared spectroscopy: IR spectra uses infra red light to determine the
concentration, structure and identify different molecules within various
organic compounds. The IR spectrometer uses rays of infrared light
which are beamed through a sample of an organic compound and
measures the absorption of light through these chemicals, resulting in a
graph, which therefore allows us to determine all of the above. It can
determine the different types of molecules as they each have a unique
spectrum quite like an individual’s fingerprint or a snow flake. Each
molecule has different vibrations which determine its unique structure
(like the dints in your finger print), as the light flows through the
compound being tested.
PTO →
Theory Continued...
The infrared light beam is sent through the sample and through the reference
sample and is sent through the spectrometer where both data samples are
correlated and a graph is produced. The graph allows us to determine the
molecules present in the compound, as each molecule will have an individual
fingerprint displayed on the graph.
Typical Uses
• IR spec is used for gathering information about the
structure of a particular compound. It is often used in
forensic science to find out what a mystery compound is at a
crime scene. Compounds usually used in IR will have a
specific movement or vibration to it. Most of the compound
used in IR are organic. IR spectroscopy is suitable when
looking at qualitative data.
• IR spec is also used in the medical field. It can be used for
cancer detection. The cancerous cells would have a
different and unique vibration compared to the other
compounds in the body and other cancers.
Examples & Explanation
• Using your data booklet, we can match the peaks to our data to see what
bonds are present. (infrared absorption data)
• At 2500-3000 there is a peak representing an O-H (acids) bond.
• At 1750 there is a peak that represents an carbon C=O bond.
• We can tell from this that the chemical present is a carbonic acid
• The peaks before 1750 is known as the fingerprint region and not much can
be learnt from that region.
Safety Precautions
• Ensure that the infrared radiation remains contained as excessive exposure to it may
result in impaired vision and other eye problems.
• The most easily tested substances that are tested using infrared spectroscopy are
potassium bromide and calcium fluoride.
• Potassium bromide is harmful if inhaled, ingested and contacted with skin. Small
exposure causes only short term irritation such as rashes, mild pain and coughing.
However, long term exposure can cause severe effects on the central nervous system,
brain, eyes and respiratory tract.
• Calcium fluoride is harmful if ingested, inhaled and contacted with skin. Small
exposure causes minor irritation such as inflammation, coughing and sneezing. Over
exposure can cause lung damage, choking, unconsciousness and if sever, death. Eye
contact can cause corneal damage and possible blindness.
• Precautions to take while handling both these chemicals would be wearing gloves, lab
coats safety glasses and if necessary, masks.
Bibliography
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http://en.wikipedia.org/wiki/Infrared#Night_vision
http://www.sciencelab.com/xMSDS-Calcium_fluoride-9927120
http://www.jtbaker.com/msds/englishhtml/p5587.htm
http://www.cem.msu.edu/~reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm
www.chemguide.co.uk/analysis/irmenu.html
http://orgchem.colorado.edu/hndbksupport/irtutor/tutorial.html
http://en.wikipedia.org/wiki/Infrared_spectroscopy
http://www.mtholyoke.edu/~mlyount/MySites/ForensicSpectroscopy/WhatIsIR.html
http://wwwchem.csustan.edu/Tutorials/INFRARED.HTM
[Chemistry 2 – 4th edition]