Finding a low-cost IR Spectrometer for reaction monitoring?

I was wondering why nobody tried to make a dispersive IR spectrometer using a diffraction grating? Using two gratings you can get resolution of 50 nm/mm (approx 30 cm^-1/mm) at the distance of 100 mm for 3.5 um grating at the range of 5000-1500 cm^-1 (2.0-6.6 um) and resolution of 120 nm/mm (approx 12 cm^-1/mm) at the same distance of 100 mm for 10.6 um grating at the range of 1700-510 cm^-1 (5.9-19.7 um):
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=86...

4000-500 cm^-1 is a perfect range for IR spectrometer, although the windows would be a problem (you don't want a dust in your grating), only potassium bromide is capable of transmitting up to 400 cm^-1.
https://www.edmundoptics.com/resources/application-notes/opt...


(there's also a caesium iodide, but it's a pain in the ass due to softness and hygroscopicity).



Interference spectrometer is much harder to make from scratch due to a very high precision required, especially beamsplitter: 1/4 wave - about 500 nm in position and geometry in every transmitting and reflecting part until detector.

If you can make windows out of NaCl or KBr, then you could actually try to make a prism out of it. However, KBr prism in the shape of equilateral triangle gives only 0.04 rad shift between 1 um and 10 nm ( http://www.janis.com/libraries/window_transmissions/potassiu... , correct me if my calculations are wrong ), thus wavelength resolution is 2000 nm/mm (approx 800 cm^-1) at 100 mm distance from prism, which is much lower then diffraction grates provide, so it's much harder to get at least 10 cm^-1 resolution required for analysis, which also leads to high required optics' precision.

Quote: Originally posted by Tdep

In response to the original (old) question on low cost FT-IR spectrometers, while there aren't any now, in the next decade or two that could become a possibility, not because FT-IR will get better, but I believe it will be superceded by new technology (and that gives the opportunity to pick up 'old' tech at low cost... Well that's the thought). What's the new tech?? Dual frequency comb lasers. It's still not quite here because Mid-IR lasers aren't all that easy but if it continues to be developed the way it has been, it may replace FT-IR as a faster/smallermore reliable outcome. Easily field deployable, no moving parts. Read more here: https://www.nature.com/articles/s41566-018-0114-7 Or maybe not, just some late night speculation

FTIR Software

Quote: Originally posted by CharlieA

If a pure substance is diluted in various proportions with an inert substance, the intensities of the characteristic absorption bands will be proportional to the amount of substance present, and likewise for a mixture of components (e.g., a mixture containing unreacted starting materials, perhaps intermediates if any, and product(s). The course of the reaction can be followed by periodically taking samples of the reaction mix and "quenching" the reaction (for example, by dilution or neutralization, or other method). The intensities of the absorption bands in the spectra of these aliquots will vary with the amounts of the various substances present.

spectroscopy can look like science fiction nature is not that simple. @beerwiz the method you proposed is an option but not "the only practical way", by making subtraction spectra you can visualize the new bonds or the disappearing of bonds without really doing anything to the sample, even if the reaction solvent absorbs IR (like water) if you subtract the spectra from one taken before you will not see it, just the new bonds