Liquid gas Chromo. for crude oil

[Giggs]

Hi all, I'm very unexperienced in GC and I'm currently analyzing some crude oil samples but seem to have a problem or maybe not, I dont know.

I added 5% Tetralin (C10H12 or 1,2,3,4-Tetrahydronaphthalene) to some of the crude oil samples, and anticapated expected the C10 group to increase noticeably but what I observed was that the C12 group increased. And this is in six different samples, whats happening here.

thanks

[John Cuthber]

It's not alltogether clear what you are doing but I presume that you are classifying things as C10 or C12 based on the retention time. The benzene ring of tetralin is rather more polarisable than the saturated hydrocarbons so it tends to stick to the coumn by van der Walls like forces better than saturated hydrocarbons of the same number of carbons. That means that it will elute later from the GC than would be expected and this might explain why it coelutes with the C12 fraction.

[Giggs]

Is there a way to set the GC or somthing to correct this.

[John Cuthber]

Probably not.

You might be able to use something else instead of tetralin. What are you hoping to find out by doing this?

[Giggs]

Actually I cannot use anythimg else, I'm using tetralin because it is saturated with Hydrogen, its usefull for my application.

[John Cuthber]

Last tme I checked, tetralin had 3 double bonds.

http://en.wikipedia.org/wiki/Tetralin

You might want to look at the decalins.

What's the aplication you are looking at?