# Determining [CO2] of a sample in ppm

I have 20mL gas samples and I need to determine the [CO2] in ppm. I have a Li-Cor 6200 with a closed loop, so essentially I will inject a volume of gas into the loop and the change in the output is how to determine the concentration of CO2.

To calibrate I'm using a standard of gas that is 5020ppm CO2, and injecting volumes of 50, 75, & 100 uL then recording the change in [CO2] in the closed loop. After calibration I will inject 50uL of sample and record the change of CO2 in the closed loop.

But how do I set up the conversion? It is spring break and I am having trouble finding help around campus.

This is what I have done.

Taking the average change in CO2 output from 3 different volumes of standard injected, the output changes 0.114 per uL of standard gas injected (5020ppm CO2). So, (5020/.114)=44035.0877. Then, I just multiply the change in output per uL of sample injected by 44035.0877 to get the CO2 ppm of the sample. My first sample I inject 50uL and the output changes by 20.2, so I divide to get the change per uL; (20.2/50=0.404). Then multiply, (0.404 * 44035.0877 = 17790.18 ppm CO2)

Is it really this simple, or is my thinking to simple?

Thanks. This is my first post, I hope I have followed the rules.