Beer’s Law Is Not a Straight Line: Amplification of Errors by Transformation

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 4 Issue 3 (1999) pp 81-88

Beer’s Law Is Not a Straight Line: Amplification of Errors by Transformation

Judith M. Bonicamp,* Kelly L. Martin, Gerald R. McBride and Roy W. Clark

Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37132

Published online: 1 June 1999

Abstract. Beer’s law plots are commonly straight-line graphs in which absorbance is plotted versus concentration. The errors in such a plot are accentuated in the high-absorbance region due to the logarithmic transformation. This paper discusses the errors inherent in all Beer’s law plots and the choices the student has available: the use of either linear or nonlinear plotting methods. An experiment is described in which student Beer’s law data are treated in several ways to find out if transformation errors are significant. The conclusion is that if the absorbance values obtained for the calibration data exceed A = 1, then nonlinear regression or weighted linear regression is indicated.

Key Words: In the Classroom; instrumental analysis; undergraduate laboratory; Beer’s law; error analysis; spectrophotometry; photometry

(*) Corresponding author. (E-mail: bonicamp@mtsu.edu)

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Supporting material Endnotes 1-4 (30 KB) 10.1007/s00897990295b