Using simple circuitry, polarizing film, and LEGO® toy bricks, an undergraduate physics student from the Ateneo de Manila University recently built an improvised polarimeter that can optically assess the purity of Vitamin C (ascorbic acid) and other chiral substances. The device has potential applications in classrooms as a learning tool and may pave the way for more cost-effective means to monitor the quality of some consumer products.
The Ateneo de Manila University Department of Physics’ Photonics Laboratory’s polarimeter setup is built mostly out of LEGO® toy bricks, polarizing film, and cheap off-the-shelf electrical components. SOURCE: Felicidario and delos Santos.
Polarimeters are invaluable laboratory instruments that can help infer the purity of a chemical by measuring the angle of rotation of polarized light that passes through the test sample. However, laboratory-grade polarimeters are prohibitively expensive, with a high-end model costing over $11,500 and a commercial manual polarimeter priced at over $1,200. This makes their acquisition and use difficult if not impossible for small laboratories and classrooms in developing countries like the Philippines.
That may change thanks to the work of people like undergraduate physics student Ryan Joseph Felicidario and his thesis adviser, Dr. Ramon delos Santos, of the Ateneo de Manila University Department of Physics’ Photonics Laboratory. Their work improved on an earlier LEGO®-based polarimeter built by Norwegian researchers Lise Kvittingen and Birte Johanne Sjursnes. The Filipino researchers modified the original design and refined the detection process to obtain reliable and accurate measurements that are crucial for ascorbic acid, whose specific rotation is relatively low.
By using easily purchased items like LEGO® bricks, polarizing film, and cheap off-the-shelf electrical components, Felicidario was able to bring the cost of the polarimeter down to just over $150. To test the device, he used two over-the-counter samples of Vitamin C (ascorbic acid) from two different pharmaceutical brands and compared the test results with known theoretical values for pure ascorbic acid. While one of the samples produced values within the acceptable range, the other sample “showed significant deviations from the expected (values), suggesting possible impurities affecting its optical properties.”
Built at a small fraction of the price of a commercial polarimeter, the Ateneo de Manila University Department of Physics’ Photonics Laboratory’s setup features improved reliability and accuracy over the original design. SOURCE: Felicidario and delos Santos
“(The) comprehensive approach combining polarimetry and melting point determination proved to be cost-effective compared to other devices typically used for purity assessment, which are often more expensive,” Felicidario and delos Santos said in their paper, “Measurement of ascorbic acid samples’ optical rotation via an improvised polarimeter for purity assessment”, which was published in the Journal of Physics: Conference Series on October 23, 2024.
“Furthermore, the findings demonstrated that the polarimeter is not only effective in practical applications, but it also offers educational benefits. Its non-black-box nature facilitates a straightforward demonstration of optical activity and polarization concepts,” the paper concluded.
