TGIR - Playing with the limits of the technique

Thermogravimetric Analyzers coupled to an Fourier Transform Infrared Spectrometer (TGIR, or occasionally TGA-FTIR) is probably the easiest of the hyphenated methods of Evolved Gas Analysis (EGA). While Mass Spectroscopy (MS) or Gas Chromatography Mass Spec. (GCMS) are more sensitive techniques, the current shortages of helium make it more difficult to run them. As the TGA heats the sample in a furnace, normally to 1000 C, hydrogen can’t be used as a carrier gas as many gas chromatographers are currently doing.

Well, I guess you could, but I think it’d probably explode or something.

Now the limits of the FTIR are well know - only asymmetric molecules are seen, sensitivity is about 1/2 percent, water and carbon dioxide in the air hide things. You can fix some of these by increasing the path length of the gas cell*, playing with the sample size and heating rate to maximize concentration, etc. But the limitations are there.

However, the plus side is that the method is relatively straight forward and the data analysis is greatly assisted by extremely good libraries and programs. While measuring CO2 and H20 can be difficult, halogens and other strong IR absorbers are relatively easy.

* Red Shift, an Italian maker of TGIR transfers lines has made gas cells of up to 16 meters.