Inferring from Infrared
Imagine if there was a way to know which watermelon is sweeter? When is that avocado going to ripen? How many calories, carbs or protein is in that shake? How your plants are doing? What’s in those pills your taking? A new low-cost handheld sensor on the market promises all those answers and more, in real time (https://www.consumerphysics.com/myscio/scio). The technology is based on near infrared spectroscopy. How does it work?
Calorific Rays: We all know that a prism can separate ordinary light into the vibrant colors of the rainbow. Back in 1800, musician and astronomer William Herschel wanted to know the temperature of each color. By placing a thermometer with a blackened bulb along the spectrum, he discovered that the red end was warmer than the blue. To his surprise, a thermometer placed just beyond the visible red part of the spectrum was even warmer. He had discovered infrared rays, although he didn’t realize it at the time. This is the same heat that you feel when you hold your hand near a fire.
Bond. Covalent Bond. Shaken and Stirred: Chemicals are arrangements of atoms, held together by bonds. You can think of these bonds as tiny springs in motion. They stretch, wiggle, rotate and twist. When they absorb energy, the natural vibrations of bonds increase. Because of quantum mechanical constraints, these increases occur only to discrete energy levels. Different bond types (C-O, or C-H) and different vibration modes result in a series of absorptions at different wavelengths. By looking at which wavelengths of light were absorbed by a compound, we can deduce what types of chemical bonds are in the sample. Absorbances in the near infrared region of the spectrum can be so complex that they give rise to unique fingerprints of different chemicals.
Citizen Science: Spectrometers built with near infrared technology used to be large, expensive and restricted to universities. That’s changing! The handheld spectrometer transmits chemical signatures to a smartphone which checks the pattern against a huge library of compounds in the “cloud” and returns the analysis to you within seconds. When you use it, not only will you be learning more about the chemical world around you but you’ll also be helping to build a database of knowledge of the stuff around us. Now that’s citizen science!
REF: An introduction to near infrared (NIR) spectroscopy. A.M.C. Davies. https://www.impublications.com/content/introduction-near-infrared-nir-spectroscopy
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