TCD Response factors question

[SemiAuto]

I have always believed something that I was told about TCD response factor being close to '1' for most compounds (except water)... therefore, using Area% methods are fine for plant production needs. Recently I found that my Weight% numbers vary up to 7% from my Area% values and water is not even a factor because I dried the sample with sodium sulfate anhydrous. Have I been wrong/misled about TCD responses and Area% methods? Are straight Area% methods really that far off of Weight% methods?

Thanx in advance to any kind soul who spends time to respond.

[chromatographer1]

You should review the Journal of Chromatography February 1967, p68ff to a review of TCD responses by thermal response and weight corrected response. Author is W.A. Dietz, Esso Research, Linden, NJ.

best wishes,

Rod

[SemiAuto]

That reference has come up but I don't have access to it. Is there a free source for it?

The reason this came up is because I made a 50% toluene 50% tetradecane by weight standard, mixed, and got 27% tol and 73% tetradecane by Area% on my TCD!!! There must be but few reasons that this could happen. How about it chromatographers?

[chromatographer1]

TCD is not an equal opportunity detector.

If other more serious words, weight % and mole % are not possible with this detector unless you correct the response according to the specific conditions of the sample involved.

This can be quite a task.

Whoever told you the response was consistent (no correction response factors are necessary) was misinformed.

The article involved discusses TCD response versus FID response and the different corrections for mole % and weight(mass) % that are necessary.

It is worth the $25 to purchase it on-line as it is a valuable reference.

You should make up standards by volume % or mass % at differenct levels and determine the correction factors needed in your analyses.

Don't be surprised if they are linear, not over a wide range, but only over a rather small range.

The temperature of the filament and of the detector body also has an effect upon the response of your analytes.

BE CONSISTENT.

Good luck and best wishes,

Rod

[Peter Apps]

In addtion to what Rod said, remember that the detector does not operate in isolation- what it detects has been injected and run through a column - either or both of which can change the composition of the sample.

Peter

[AICMM]

I can empathize on the difficulty in getting articles. I often have the same problem. Having said that, LCGC magazine has a good on-line article (Hinshaw) that discusses the fundamentals and a little bit about the broad differences in thermal conductivity.

If you can tell me what journals you do have access to I might be able to guide you to some other articles as well.

Best regards.