Hi

In ppm the concentration will not change. However you'll get a different spectrum intensity because the molar or mass concentration will change. The spectral signal depends on the amount of molecules in the beam's path. In your case the temprature and the pressure didn't go up the same and didn't save the same ratio so your molar concentration (n/V) has changed (on the basis of pv=nRT). The beam will encounter less molecules of CO2 and the absorbtion intensity will be weaker. The spectrum would have been the same if your V would have remain constant (you would have recieved a higher pressure) This is correct only if I understood your experimental setup...maybe you can explain more about your system (closed loop? Flow through?).

Okay- thanks for the insight!

I am flowing the gases through the gas cell and just venting it into a fume hood. So, my feed is set at a constant standard flow at ambient conditions (using digital mass flow meters), fed to a heated line and heated gas cell, then vented out. The heated gas cell and heated line are necessary to protect the components, so increasing the temperature is required.

Thanks!

Yes, the concentration of CO2 in your sample will still be 111 ppm, not affected by the temperature & pressure changes. The CO2 concentration changes with T and P only when it is expressed in m/v, not in m/m or v/v.

Hope this helps.

Thank you- that's what I was thinking. I even tried a trial or two with volumetric flow to check. They gave the same curved results. I was over-thinking the problem.

I believe the reason for the curved calibration curve is actually due to the nature of the detector/machine components, not my sampling methods.

Thank you for your help!