Fourier Transform Infrared Spectroscopy

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Fourier Transform Infrared Spectroscopy
November 15, 2006 CH EN 4903 Chad Wilding
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Outline

• What is Fourier Transform Infrared (FTIR)
  Spectroscopy?
• Why use FTIR?
• The importance of a good baseline
• The analysis of aqueous sugar solutions
• Conclusions
• References

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What is FTIR?

• Passes infrared (IR) light through an
  interferometer
• IR light passes through a sample and an
  interferogram is obtained
• A Fourier Transform is performed on the
  interferogram and a spectrum is defined for the
  sample

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Diagram of a FTIR
http//en.wikipedia.org/wiki/ImageInterferometer.
png
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Why Use the FTIR?

• Identify constituents of organic compounds
• Determine the existence of light hydrocarbon
  gases
• Analyze the concentration of aqueous sugar
  solutions

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Obtaining the Baseline

• Spectra were referenced against the baseline
• Distilled water was used as the background
• Baseline needs to have virtually zero absorbance
  or minimal error

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Analysis of Sugar Solutions

• D-Fructose crystals dissolved in distilled water
• Sucrose crystals dissolved in distilled water
• Sucrose is a combination of a glucose ring bonded
  to a fructose ring

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Fructose Spectra
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Sucrose Spectra
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Calibration Graphs
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Calibration Equations

• Fructose
• Conc. (log(1/R)0.0529)/0.0004
• Sucrose
• Conc. (log(1/R)0.0314)/0.0003

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Unknown Spectrum
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Results

• Sucrose concentration-79.0 11.7 g/L.
• Fructose concentration-253.5 11.7 g/L.
• Actual sucrose concentration-60 g/L.
• Actual fructose concentration-240 g/L.

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Conclusions
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What is a Good Baseline?
s1 0.226 s2 0.015 s3 0.015
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References

• Schwedt, Georg. The Essential Guide to Analytical
  Chemistry. New Jersey Wiley and Sons, 1997.
• Crocker, Betty. Chemical Engineering and
  Brownies, 1971.
• Wikipedia. Fourier Transform Infrared
  Spectroscopy. http//en.wikipedia.org/wiki/fourier
  _transform_infred_spectroscopy. 2006

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Questions and Answers