How to calculate propane concentration in headspace vial

[lwd]

I have a school project that requires me to quantify propane gas via a gc fid instrument. A 40ml headspace vial was filled with propane gas and capped. I injected 100ul of the gas into the gc fid, and am trying to figure out what the formula is to know what the concentration of propane is.

this is supposed to be my standard. I am supposed to then inject an unknown and calculate the propane in it based off of the chromatogram of the standard that I injected.

this is all very new to me, I'm not a chemistry major, and am a bit lost how im supposed to quantify my unknown if I dont know what concentration my std is.

I know 1mol of propane = 44.09g/mol
from that I am supposed to calculate how many ml it occupies at rm temp, which I can then calculate the weight of the propane in the 100ul syringe that is to be injected. Im just not sure how to do that calculation

[rb6banjo]

There is a "Student Project" section of this forum. This question is probably more appropriate for that.

Perhaps I'm missing something but if you fill the vial with propane (I'm assuming atmospheric pressure) isn't it 100% propane? Also, I'm assuming that your chromatograph is set up correctly by your instructor or someone who knows about this stuff for your analysis. If all of these assumptions are valid then the rest of this will make sense and it should work.

If you inject 100 µL of that gas you get a response (R) which corresponds to 100% propane (at RT and atmospheric pressure).

R = A*100

R/100 = A (A is called your response factor)

The response factor is a proportionality constant that allows you to convert an instrument response (area counts, peak height, etc.) to the concentration of the analyte in the standard.

Now, if you inject 100 µL of your sample (it is critical that your injection volumes are the same for sample and standard) and get a response (Rs)

Rs/A = % Propane in your sample.

As long as your sample is also at atmospheric pressure, the same temperature as your standard, and you do not have any interference from other components in the sample.

Generally, we like to make multiple standards of different concentrations to generate calibration curves but the FID is pretty linear over a very wide range and if your sample is not too far from your standard, it should be fairly accurate.

If your sample comes back as 56% then in a 40 mL vial, that's 0.56*40 = 22.4 mL of propane in your vial.

Good luck. Remember, good analytical chemistry knows that there are no absolutes. You should (if you can get the instrument time) inject your sample and standard multiple times to get an idea of the statistical confidence you have in your measurement.

[CE Instruments]

Dumb answer for dumb question.

On the assumption your 40ml vial is filled with Propane and you inject 100ul your standard is 100%. Inject 100ul of any mixture and then relate that to the peak size of your "100%" standard Simples