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Signal-to-Noise Ratio, Signal Processing, and Spectral Information in the Instrumental Analysis Laboratory

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Jonathan P. Blitz and Douglas G. Klarup

Department of Chemistry, Eastern Illinois University, Charleston, IL 61920

J. Chem. Educ., 2002, 79 (11), p 1358

DOI: 10.1021/ed079p1358

Publication Date (Web): November 1, 2002

Section:

History, Education, and Documentation

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.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Analytical Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Instrumental Methods

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  Journal of Chemical Education2007 84 (8), 1331
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