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  Home > JCE Print > Journal of Chemical Education > Issues > 2002  > November  >
In the Laboratory
Signal-to-Noise Ratio, Signal Processing, and Spectral Information in the Instrumental Analysis Laboratory
Jonathan P. Blitz and Douglas G. Klarup
Department of Chemistry, Eastern Illinois University, Charleston, IL 61920
Cover
November 2002
Vol. 79 No. 11
p. 1358
Abstract
A laboratory is described that illustrates concepts related to the signal-to-noise ratio, spectral data acquisition parameters, and signal processing. The laboratory is designed to illustrate the compromises one must make between signal-to-noise ratio, spectral information, and analysis time. Using an FTIR spectrometer, the signal-to-noise ratio is obtained as a function of spectral resolution and frequency range. The S/N increases with decreasing resolution, and can be correlated with the single beam signal intensity. Digital smoothing with various numbers of smoothed points is performed to illustrate how the S/N can be enhanced. A plot of signal-to-noise ratio versus the number of scans co-added (at constant resolution) fits a power curve with an exponential very close to the theoretical value of 0.5. Single-beam atmospheric CO2 spectra are obtained at various resolutions to illustrate the loss of spectral information at low resolution. Spectra are compared after applying digital smoothing routines to a high resolution spectrum to illustrate the potential drawbacks of this S/N enhancement technique.
Supplement
The student instructions for conducting the experiment and preparing the lab report are available.
*  Contents JCE2002p1358W.doc (Microsoft Word)
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*  Citation
 Blitz, Jonathan P.; Klarup, Douglas G. J. Chem. Educ. 2002 79 1358.
*  Keywords
 Analytical Chemistry; Instrumental Methods; Laboratory Instruction
*  History
 Created:
Last Updated:		 September 30, 2002
March 16, 2005
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