Micro TCD

[neo_jm24]

Hi,

Can someone please advise what is the lowest detection level of micro TCD using Argon for carrier gas? And is it appropriate to use Argon gas as carrier gas for capillary column? Thanks

[chromatographer1]

According to Agilent's document which took 10 sec to find doing an Internet search,

• Detection limit capillary columns 1 ppm and Micro-
packed/Plot columns 10 ppm (Component dependent)

Perhaps you might like to learn how to use the internet to get information, oops, you did ask the Forum, didn't you?

best wishes,

Rod

[neo_jm24]

Oh yes...sorry for bothering you, maybe it was not a good time for you. Thanks for your "KIND" reply though. I have also seen that article you replied and that is using HELIUM as carrier gas (MS 5A for methane and CO). Actually the FORUM is the last thing I ask after I have tried searching articles, research and the internet to get the "HELPFUL" information.

Thank you very much ROD.

[chromatographer1]

ouch ouch ouch

You got me where I deserved it.

But to further answer your question which I screwed up, argon has a different thermal conductivity. It is less sensitive to most commonly used analyte gases. So your question has great import.

But if you go do an encyclopedia of physical data (which I don't have) you can compare the values and get an idea of the DIFFERENCE between conductivities between Argon and whatever gas you wish to compare versus that gas with helium.

The ratio of the differences should give you an accurate idea of the limit of detection as compared to helium as long as you are using the same volumetric and linear flow rate.

truly best wishes,

Rod

ps it was early and before my morning coffee, but no excuses my apologies.

[Johnny Rod]

http://www.engineersedge.com/heat_trans ... -gases.htm

What analytes are you looking for? And why do you want to use argon as carrier?

[neo_jm24]

Thanks a lot Rod. I know it is not the way you impart your knowledge since I have joined this forum. Yes I maybe new on this forum but you reply and answered queries professionally. But its ok maybe I was just not in the right timing my apologies. Thank you very much though. Your are really very good in these area. I think all or most of the queries I can see you name and replies. Thank you again and apologies on the off timing.


Humble regards!

Mark

[neo_jm24]

Johnny Rod & Rod (chromatographer1),


I actually would like to use Argon as carrier gas to for my components of interests which is Hydrogen, Nitrogen, Methane and Carbon Dioxide. Basically this actually a research on Biogas so I will be using Gas Chromatograph analyzer and I will be using 2 capillary column and micro TCD as my detector. I know that micro TCD have 50ppm lowest detection level using Helium carrier gas but with Argon I don't have any idea. I don't have idea on the lowest detection level for micro TCD using Argon, I actually do not have any idea using micro TCD(training). My primary concern of analysis on this research is Hydrogen and Methane.


Thanks

[chromatographer1]

Argon Thermal conductivity 0.0177 W·m−1·K−1

Hydrogen Thermal conductivity 0.1805 W·m−1·K−1

Helium 0.1513

Methane 0.0300

CO2 0.0146

CO 0.0230

As you can see methane and CO have some difference to Argon, so you should see SOME levels, but not nearly as good as you will see hydrogen.

ethane, ethylene, etc have about the same TC as CO2 and Argon, so they are NOT detected well.

It is the difference in value which creates the sensitivity of the detection of the gas.

Do the calculations yourself.

These values change with changes in temperature and are for reference only (20C).

best wishes,

Rod

[chromatographer1]

If you don't mind me telling (suggesting) you what to do,

if you had a carrier gas composed of 50/50 argon and hydrogen, how would this affect the detection of all the gases involved?

Please post your answer, if you would.

best wishes,

Rod

[chromatographer1]

Dear Mark,

please send an amount of money equal to the value you give to about 20 minutes of my time finding this information for you or $100, whichever is greater.



Golly, I am stilling waiting for all the other checks to roll in. This being unemployed without an income isn't easy.

I hope you find (have) a job when your research is over.

best wishes,

Rod

[neo_jm24]

Rod,

Nothing I can say sir... Actually one also of my problem is what you are asking MONEY but the I don't think this forum can help with that I'm actually also looking for one.

I am just thinking regarding to what you are asking

"If you don't mind me telling (suggesting) you what to do,
if you had a carrier gas composed of 50/50 argon and hydrogen, how would this affect the detection of all the gases involved?
Please post your answer, if you would."

To my understanding that all GC detectors should have different response or lowest detection level varying on the carrier gas. e.g. micro TCD on using Helium is 50 ppm. On my concern what should be "SAFE" lowest detection level to say when I am using Argon on micro TCD.

Above all of it Thank you very much ROD. indeed thank you!

[chromatographer1]

A SMALL lesson

A TCD 'sees' the difference in the thermal conductivity between the carrier gas and another gas eluting in the detector. This difference in the conductivity of heat produces a different temperature in the detector wire and the reference wire which gives a different resistance to an electrical flow through the wires and this difference in current is what the detector 'sees' and is measured.

Normally, a pure gas is used for a carrier (a reference) gas to minimize 'noise'. As you can see in the values of the conductivity that those of helium and hydrogen are about the same, but both are quite different from the other gases, hence their common use as a carrier gas to detect these other gases.

But hydrogen being similar to helium does not detect well when helium is used as a carrier. So nitrogen or air is commonly used as a carrier gas for hydrogen detection.

Argon can be used instead and you will get adequate detection for hydrogen, and some for methane and a few other gases, but most do not detect well.

Consider what happens to the conductivity of a carrier composed of a 50/50 mixture of H2 and argon.

Could you measure hydrogen in a sample? Methane CO2, ethylene, using a mixture for a carrier gas ?

(and of course, I do not expect the check is in the mail)

best wishes,

Rod