Hello,

I am using an Agilent Cary 660 FTIR equipped with a custom 10 M path length gas cell and both MCT and DLaTGS detectors and operating on the resolutions pro software.

I am trying to measure trace impurities in gases using an FTIR as opposed to a GC and so far it has been working very well. My main issue at this point is trying to find out at what level CO2 saturates and a way to accurately measure co2 in the ~1000 ppm range.

For CO2 in the lower ranges (around 1-100 ppm) I have curves that work very well but at some point the CO2 band around 2350 cm^-1 becomes saturated and no longer gives me a linear response.

I am using the MCT detector with a 0.1 cm^-1 resolution and an aperture size 0f 0.5 cm^-1 @ 4000 cm^-1. Zero filling 8 and Happ-Genzel apodization.

I usually run the scans at atmospheric pressure but tried to run the CO2 scans at -13 PSIg to reduce the CO2 peak height and then back calculate to find the concentration at atmospheric pressure but it is hard to hold the cell at -13 PSIg so I can't run many scans and I am getting poor repeatability, most likely from leaks associated with the low pressure.

So now my thoughts are to do some combination of the following three:

1) Adjust the aperture size to adjust for saturation by limiting the signal

2) Adjust the pressure of the scans to adjust for saturation by simulating a lower concentration and back calculating

3) using the DLaTGS detector instead of the MCT since it is less sensitive and should give me a higher cutoff for saturating my CO2 band.

If anyone has any experience with this at all, or gas analysis on the FTIR at all, or just CO2 IR help at all it would be greatly appreciated.