By Anonymous on Sunday, November 2, 2003 - 10:54 pm:
Hi.
I am using Agilent 6890N GC (FID). I calibrated my column with a mixture of 9 compounds and 1 internal standard. My lecturer asked me to calculate the response factor manually, and I did that by using the area ratio over amount ratio.
My question: Will response factor for a compound (eg. dodecanol) varies for different GCs (with same detector, FID)? My coursemates mentioned that there is a standard response factor for each compound that we can refer from handbook . Is that true? Pls advice.
By Rodney on Monday, November 3, 2003 - 05:18 am:
In my experience I have found that many analytes do reproduce their response factors on FID. Most FID detectors are optimized for response and act similarly responding to the presence of analytes.
For example: methanol has a FID response factor of 1.66 to a n-propanol internal std. Ethanol has a response factor of 1.22 to n-propanol.
These factors are the same on HP, or Varian, or PE chromatographs. I have used HP 5740, 5890, 6890, Varian 3500, 3600, 3700, 3400, and PE 900, 3920, and Sigma 3B. (I hope that last statement doesn't show my age. Ooops, too late!)
Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823
814-359-5737 voice
814-359-5459 fax
rgeorge@sial.com
By Anonymous on Monday, November 3, 2003 - 05:23 am:
Basically, if:
a) the FID is operating under optimum conditions e.g. fuel gas and ionisation voltage.
b) no other factors, like adsorption of your dodecanol, in another part of the system.
then the RELATIVE SENSITIVITY of the FID between compounds should be the same as in other GCs. So, yes, tables of relative sensitivities do exist.
For example if you have an internal standard of a hydrocarbon and allot the area a value of 1.0 then you will find that an equal weight of dodecanol will have a smaller area. This is because the FID responds to carbon that can be burnt to give CO2, and part of the weight in the dodecanol is oxygen, to which the FID doesn't respond.
So,RELATIVE to say heptane, the FID response to alcohols ranges from 0.23 to 0.85 depending on the alcohol and for acids between 0.01 to 0.65. You will probably have to multiply your dodecanol area by about 1.2 to get the right area for quantitation.
Hope that helps (a bit)
Ralph