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Applied Electronics: Construction of a Simple Spectrophotometer

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Melissa A. Thal

Department of Chemistry, Indiana University, Bloomington, IN 47405

Michael J. Samide

Department of Chemistry, Butler University, Indianapolis, IN 46208

J. Chem. Educ., 2001, 78 (11), p 1510

DOI: 10.1021/ed078p1510

Publication Date (Web): November 1, 2001

Abstract

In this paper we describe the construction of a simple spectrophotometer intended for use as a capstone circuit for an electronics laboratory exercise. Students in the undergraduate laboratory have learned basic circuitry and are now able to read a schematic and construct an instrument that has practical applications in chemical analysis. A simple LED is used as the source and is easily changed to correspond to different species being studied. Detection is accomplished through the use of one of three signal transducers (a photoresistor, a photodiode, or a photodarlington) and a current-to-voltage converter. A box lined with black felt is used to shield the spectrophotometer from ambient light. This spectrophotometer shows excellent Beer-Lambert law linearity over a large concentration range and has been used in the laboratory to determine the concentration of a metal cation in solution on the basis of a calibration curve. Of the transducers used, the photoresistor showed the best response at multiple wavelengths with error in concentration determination not greater than 6%. Through the building and testing of this circuit, the students can visualize applications of electronic circuitry.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Laboratory Instruction

Keywords (Feature):

Topics in Chemical Instrumentation

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Instrumental Methods

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