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.
Highlights
Students encounter polarimetry in high school in connection with stereochemistry
We have previously published descriptions of simple instruments constructed with plastic interlocking toy bricks, such as Lego, and LEDs for UV−vis absorption and fluorescence measurements intended for student experiments.12−14 We add here polarimetry, extending the range of spectroscopic methods possible with the same basic building blocks
We present here identification of unknown samples of Dfructose, D-sucrose, and D-glucose; quantification of (R)limonene in citrus ski wax remover; and determination of enantiomeric excess in a mixture of D- and L-arabinose, as well literature values
Summary
Students encounter polarimetry in high school in connection with stereochemistry. The classical schematic representation of a polarimeter is illustrative and easy to understand, an asset not shared by the modern polarimeter, where basic features are hidden. Applications are presented: finding the enantiomeric excess in arabinose solutions and limonene in a citrus ski wax remover as well as the optical rotation of honeys, syrups, and essential oils. Arabinose is harmless and water-soluble and has a high specific optical rotation It is a suitable compound for investigating quantitative aspects such as enantiomeric excess (ee, most commonly given in %) in a mixture of enantiomers. Having performed measurements with glucose, fructose, and sucrose, it makes sense to continue with an industrial application of polarimetry on sugar-containing compounds such as in analyses of honeys and syrups.−. Measuring the optical rotation of essential oils shows the diversity of optically active compounds in natural compounds The net rotation is, dependent on all University College, 1757 Halden, Norway; orcid.org/0000-
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