Demonstrating Basic Properties and Application of Polarimetry Using a Self-Constructed Polarimeter

Abstract

An easily constructed and inexpensive polarimeter with an optical rotation angle resolution of about 0.5° is presented. It is made from small pieces of polarizing film, 2 LEDs, a protractor, and a few wires, all held in place with plastic interlocking toy bricks, such as Lego bricks. The instrument was used to demonstrate the optical rotation of plane polarized light as a function of concentration, path length, temperature, and wavelength, and to determine enantiomeric excess in solutions of arabinose, the amount of limonene in citrus ski wax remover, and optical rotations of various types of honeys and essential oils. Results were comparable to values obtained on a commercial scientific instrument, and with literature values.

Figure 1

Self-constructed polarimeter. (a) From left to right: LED used as a light source (592 nm), polarizing film fixed between two Lego bricks, sample cuvette, and second polarizing film superimposed onto the end of a plastic dial that can rotate around the protractor. (b) LED used as a detector connected to a multimeter with a high internal resistance (>10 MΩ).

Figure 2

Optical rotation vs concentration for (R)-(+)-limonene (diamond) and (S)-(−)-limonene (circle). Self-constructed polarimeter: filled symbols; wavelength = 592 nm; path length = 4 cm. Anton Paar: open symbols; wavelength = 589 nm.

Figure 3

Optical rotation vs path length for d-(−)-fructose (0.5 g/mL). Wavelength = 592 nm.

Figure 4

Optical rotation vs temperature of d-(−)-fructose (0.5 g/mL). Wavelength = 592 nm. Path length = 4 cm.

Figure 5

Specific rotation vs wavelength. d-(−)-Fructose and d-(+)-sucrose both at 0.5 g/mL. Self-constructed polarimeter: filled symbols; wavelength = 405, 428, 470, 500, 525, 592, 626, 635, and 660 nm; path length = 4 cm. Anton Paar: open symbols; wavelength = 436, 546, 579, and 589 nm; path length = 10 cm. Extracted values from Mahurin et al.: star symbol.