Consider you have a standard cylinder having Methane (10 mole%), ethane(20 mole %), and propane (30 mole%), and balance N2 (40 mole%)
Step 1: Do the GC of this standard, you will get the peak area of methane ethane and propane, respectively
Step 2: (You will have this option in the calibration table in GC software)
Calculate response factor (Amount/area)
So response factor for methane = 10mol%/ area of methane
response factor for ethane = 20mol%/ area of ethane
response factor for methane = 30mol%/ area propane
***I am assuming here area of methane ethane and propane is 20, 40, 60
So response factor for methane = 10mol%/ 20 = 1
response factor for ethane = 20mol%/ 40 =1
response factor for methane = 30mol%/ 60 = 1
Step 3 :
Inject an unknown sample and get the peak area of methane, ethane, and propane
Calculations for the unknown sample
a. Amount of methane in the sample (mole%)= response factor of methane (1) * area of methane
b. Amount of ethane in the sample (mole%)= response factor of ethane (1) * area of ethane
c. Amount of propane in the sample (mole%)= response factor of propane (1) * area of propane
** I am assuming you get 30, 40, and 10, methane, ethane, and propane respectively
Now as it is not 100% we need to normalize
Step 4: (GC do it automatically when norm% option is selected )
Methane (mole%) = 30/(30+40+10) = 37.5
Ethane (mole%) = 40/(30+40+10) = 50.0
Propane (mole%) = 10/(30+40+10) = 12.5
Notice now its 100 %
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If you are calculating the volume of gas (say in 1 hr, 1 Lit) and want to find the weight of the methane ethane and propane respectively then
Calculate total moles of the gas by dividing 1 lit by molar volume at STP
So Mole of gas = 1/ 24.5 = 0.041
Weight of Methane = (37.5/100)*0.041 * molecular weight of methane ( which is 16.04) = 0.25 g
Similarly, you can find the weight of ethane and propane
Source: Dr Suresh
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