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Salt vs. Sugar in the SWIR

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#1 Andy Perrin

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Posted 21 February 2017 - 05:31

The following two spectra suggested an experiment.

Edmund Scientific's sodium chloride spectrum

M. Blanco and M. A. Romero. Near-infrared libraries in the pharmaceutical industry: a solution for identity confirmation. Analyst, 126:2212–2217, 2001.

Attached Image: Sodium Chloride NIR-SWIR spectrum.jpgAttached Image: Sucrose NIR-SWIR spectrum.jpg

And, indeed, they seem to behave as advertised! Salt on the left, sugar on the right, of course.

Visible, 1064BP30 (with Noflexar lens), and 1480-1600nm phosphor + Thorlabs BBAR-coated SWIR lens
Attached Image: salt-sugar SWIR.jpg

Edited by Andy Perrin, 21 February 2017 - 05:33.


#2 Andy Perrin

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Posted 21 February 2017 - 19:54

Salt (left cup) vs. sodium bicarbonate (white), Miralax (gray), sugar (dark gray) in the right cup.

Attached Image: IMG_1453 small.jpgAttached Image: DSC05039-40 salt sugar baking soda Miralax halogen SWIR Thorlabs 50mm F4 20%22 iso200 small.jpg

Edited by Andy Perrin, 21 February 2017 - 19:55.


#3 igoriginal

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Posted 21 February 2017 - 21:05

Fascinating.

In light of this test (no pun intended), I wonder if variability in the ratio of glucose-to-fructose has an effect on reflectance and/or absorbance of table sugar ("sucrose").

After all, sucrose is actually a disaccharide, which means it is composed of a mixture of two sugar molecules - glucose and fructose - both of which on their own are monosaccharides.

In fact, an even bigger question comes to mind: Are the above-observed spectral responses attributed to glucose, only? Or fructose, only? Or would both monosaccharades exhibit the same spectral response? It would therefore be a curious experiment, if you were to isolate each monosaccharide on its own (a sample of pure glucose powder, and a sample of pure fructose powder), and then do a comparative test of the two monosaccharides side-by-side.

This would reveal if the above spectral response is more specifically attributed to only glucose, or only fructose, whereas testing a sample of sucrose (given that it contains both, glucose and fructose) does not disclose this.

It would be interesting, indeed, if such a test would reveal that glucose and fructose are not identical in spectral response. Hmmmmm.

Edited by igoriginal, 22 February 2017 - 01:21.

Igor Butorsky

#4 Hornblende

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Posted 22 February 2017 - 00:58

Ohhh, that is so interesting!
Keep going :)

#5 DaveO

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Posted 22 February 2017 - 02:32

When chemists measure IR spectra they use a frequency scale, not wavelength, so these are in cm-1

Attached Image: Glucose & fructose A.JPG

Attached Image: Glucose & fructose B.JPG

They are only screen shots but you get the drift. In fact IR tends to show the vibrations of the chemical groups involved at characteristic frequencies to provide the so-called IR signatures of molecules.

In the dark ages when I was at Uni in the 60s (1960 not 1860!) IR spectroscopy was just being introduced as a way of identifying organic molecules (organic means carbon containing - it has no relationship to the "touchy-feely fruit-loopy" meaning applied today by all those who believe in magic crystals)

IR spectrometers originaly had moving prisms, then came gratings and finally Fast Fourier Transform FFT instruments whcih can pull amazing signals out of noise.

Dave

#6 Andy Perrin

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Posted 22 February 2017 - 03:02

Those are way out in the long wave infrared if you convert the cm^-1 to nm. 900cm^-1 = 11111 nm, and 1400cm^-1 = 7142nm, which is actually in the range of my FLIR thermal camera (8-13 microns). To see what they do in SWIR we need 1400-1600nm or so, which is in the 6000cm^-1's.

Most of the FTIR spectra I see from chemists seem to be in the 4000-1000cm^-1 range, which corresponds to 2.5-10 microns, the medium wave infrared area. If I could get a camera that worked in that range and some filters, I bet the images would be pretty awesome!

Edited by Andy Perrin, 22 February 2017 - 03:43.


#7 OlDoinyo

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Posted 23 February 2017 - 03:00

Sodium chloride is often used for sample holder plates in infrared spectroscopy; ground pelletized samples can also be prepared with NaCl, although KBr is favored because it is a bit softer. Being ionic solids, the salts have no bond-vibration modes to create absorption peaks. Sugar, on the other hand, is a covalently bound molecule and does possess such modes.

#8 Andy Perrin

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Posted 23 February 2017 - 03:39

I think you must mean rotation modes? They can definitely vibrate; you can have the Na-Cl-Na-Cl's get closer and farther apart, like:
...Na---Cl---Na---Cl...
...Na--Cl--Na--Cl...
...Na-Cl-Na-Cl...
...Na--Cl--Na--Cl...
...Na---Cl---Na---Cl...
...Na--Cl--Na--Cl...
...Na-Cl-Na-Cl...
...Na--Cl--Na--Cl...
...Na---Cl---Na---Cl...
...