A very simple refractive IR spectrometer is possible for under $1000 if you can live with 2-10μm range. I don't have a full write up yet but the basic design is an MLX90614 thermopile scanning infrared light generated by nichrome wire, focused with a zinc selenide CO2 laser lens (the ones without an AR coating are better but harder to find), and separated by a silicon prism which is essentially just a chunk of a broken silicon boule. It's very difficult to find transparent materials in this wavelength range, especially when you're limited to cheap goods mass-produced for some other application. Signal noise and speed will be much worse than a modern FTIR but it's usable when calibrated.

It might work for qualitative measurement (what is the solution you are measuring), but this kind of instrument will not be performant enough to do qualitative analysis. Once you want to measure amounts the FTIR is probably the only way to go, especially with more complex solutions.

There is Neospectra [1] company that produces FTIR-on-chip modules. Performance is not that great compared to research grade FTIR, but the price is a lot less.

[1] https://www.neospectra.com/

How is FTIR used for drug testing? Is it used to test for contamination based on the spectrum profile?

Peaks of each chemical is unique so you can scan database of known chemicals and compare.

You can even measure the amounts of various chemicals in solution, but that would require complex calibration. In this case you are basically writing ML system that is trying to fit various peak heights/areas to amount of compound.

This doesn't really explain how but it does talk about the uses of an FTIR in a drug checking, harm reduction situation.

https://globalnews.ca/news/4540315/new-drug-checking-machine...

Not an expert, but if you can test for contamination why wouldn't you be able to test for the drugs themselves?

Raman spectroscopy[1] is one that I know of that is frequently used to determine chemical composition. Spectroscopy in general still amazes me.

[1] https://en.wikipedia.org/wiki/Raman_spectroscopy#Application...