Jeri Ellsworth (after a brief intro to mass spectroscopy) demonstrates a very simple DIY mid-infrared spectrometric detection of a fluorocarbon using a soldering iron as a black-body radiation source, an infrared detector from a home security motion sensor as the detector (starting around 3:00 in the vid). This is truly amazing and although it doesn't address the issue of filtering for a specific wavelength, is a very impressive use of common household materials to do mid-infrared sensing! Video is long but definitely worth the watch!

I wonder if a reflective grating and a slit could help separate out wavelengths and make a full mid-infrared spectrometer possible at DIY costs.