By Ian on Tuesday, May 27, 2003 - 02:24 pm:
Anyone aware of literature describing the mathematical calculation of FID response factors using structural data from a molecule. Please note: I know how to determine response factors experimentally using standards, but my question refers to cases where one does not have the standard, but want to calculate the expected response factors.
Thanks very much
By m on Wednesday, May 28, 2003 - 01:44 am:
try searchin for the Kovac index?
hmm, no, that is for retention times.
By Les on Thursday, May 29, 2003 - 10:46 am:
Caw atomic weight of carbon 12.011
Cn number of carbon molecules in the group
Haw atomic weight of hydrogen 1.008
Hn number of hydrogen in the group
0.7487 corrects the response of methane to unity
FID response factor =
= (((Caw*Cn)+(Haw*Hn))/Cn * .7487)/Caw
By Ian on Thursday, May 29, 2003 - 01:35 pm:
Excellent....Thanks Les.I will certainly try this out. At a first glance it seems that this formula will work for common hydrocarbons. It would be interesting to see how well oxygenated hydrocarbons also fit this.
Once again...Thank you very much.
By Marcel van Duyn on Friday, May 30, 2003 - 05:25 am:
Ian,
Try searching the literature for Sternberg and Kaiser. I use Sternberg an he discribes mathimatical calculations for FID respons factors, based on effective carbon number. The correction for a number of hetero-atoms (eg O an Cl) but also on different C type (alifatic, aromatic, olefinic)are in his table. I have compared a lot of the determined ones against the calculated ones and with the odd exception (eg Methanol but also the triple-bonds) the calculated ones differ by only a few percent, wich I think is very good. Good luck.
By Anonymous on Friday, May 30, 2003 - 05:59 am:
Ian
You should assume the uncertainty of RFs of oxygenated compounds to be up to 10% and not as good as authors such as Sternberg and Kaiser may have believed at the time. The reason I say this is that I once measured FID RFs on a dual detector system with one injector split to two columns. The two FIDs were set up as identically as possible. Their relative response factors were consistent to <5% for hydrocarbons and some chlorinated hydrocarbons, but much worse for alcohols and glycol ethers. Perhaps your experience will be better. If you try only one column/FID you won't know for sure.
By Ian on Monday, June 2, 2003 - 12:17 pm:
Thanks to all of you for your valued contributions. Chromatography remains a facinating science !!!
Ian