Accurate, Photoresistor-Based, Student-Built Photometer and Its Application to the Forensic Analysis of Dyes

Student-built photometers are recognized as being useful tools in teaching laboratories that help students understand the concepts behind experimental measurements, and several devices have been reported that employ photoresistors as the detector of choice. We demonstrate here an improvement over these instruments and the analyses thereof, providing more rapid deployment in the laboratory and also considerable increases in both linearity and accuracy. This was confirmed by conducting quantitative absorption spectroscopy of known concentrations of potassium permanganate solution. A laboratory exercise utilizing this approach was employed in two postsecondary institutions to simulate the forensic analysis of unknown fabric dyes to determine the identity and concentration of an unknown dye solution.