Chromatography Forum

I woud like to ask you if it is posible to determine the total organic carbon (TOC) of a mixture without separation by FID? Its a mixture of unknown organic compounds ( like benzene, toluene, butane, undekane, styrene, cumene ..... ) Thank you.

I believe a company in Texas has offered a TOC unit that purged water and trapped the hydrocarbons and sent them as a simple unseparated plug to a FID for quanitation. Since many of the volatile hydrocarbons that have any solubility in water have a similar response by weight in the FID a measurement was then deemed possible.

Can you kindly give a few more details to your situation?

General questions generally get general answers and that is probably not an accurate solution to your specific need, is it?

best wishes,

Rod

Isn't the FID response subject to change as a function of the non-CH groups present? I'm thinking that a little halogen presence could go a long way to throw off a TOC result...

Dear Dr.

You have right, and this is the biggest problem with this setup, that there is a mixture of unknown organic-hydrocompounds and we woud like to determine the total organic carbon. Well I think it is unpossible with FID ( it is posible, but the standard deviation will be somewhere +/- 40 % .

Thank you for your time

Dear Rod

Well it can be, you are able to determine the TOC by FID if before the detector you are reducting the sample to methane and you are analyzing a known compound or:
(1) where only one compound is known to exist;
(2) when the organic compounds consist of only hydrogen and carbon;
(3) where the relative percentages of the compounds are known or can be determined, and the FID responses to the compounds are known;
(4) where a consistent mixture of the compounds exists before and after emission control and only the relative concentrations are to be assessed; (5) where the FID can be calibrated against mass standards of the compounds emitted (solvent emissions, for example).
It´s in EPA 25 method.

Thanks Zoli

Hi hajduzoli,
After your new posts, I think I (maybe DR and Rod as well) misunderstood your question. Or maybe I just couldn't understand what you were asking. Could you please elaborate?
Thanks

Zoli seems to have answered his own question.

Please note that I was not making any claims of my own, only reporting an example of one situation that I had seen.

The application which Zoli specifically did not mention was general and I noted that in my post.

Any FID responds differently to different carbon bearing molecules as is quite well documented in the literature.

Even helium ionization detectors are not completely linear in their response.

The application which I did see this TOC analyzer was in fact testing water from a boiler where oil contamination from pumps etc needed to be detected before any leak became extensive and expensive damage was done.

I hope every one is satisfied with the information shared on this thread.

best wishes,

Rod

While I can conceive of doing VOLATILE organic carbon by FID with no separation step (with all the caveats about response factors) I cannot see how you can do TOTAL organic carbon by any gas phase method since large quantities of organic carbon (say sugars for e.g.) are completely non-volatile.

Peter

Hi to all

Well we are working for one oil company and they wanted to determine the TOC emissions by FID I was looking for some informations about this method.

Thank you for your time and answers

Zoli