Chromatography Forum

Anyone using or considered using a liquid helium supply rather than UHP tanks?

What about using Argon as a carrier gas?

Generally speaking,

H>He>N>Ar in terms of separation quality, as a function of carrier gasses.
Not only is H better than He, N etc, but it's cheaper and there's no shortage!

If you're looking for a change, consider changing to H.

Fat Johnny,

Regarding helium dewars, to do this you would need a pressure builder loop and unless you are using a LOT of helium you will probably vent as much helium as you use. Cylinders don't vent, so what you buy is what you get.

Regarding argon carrier, try it and you will see. It will be an eye opening experience. I did the same thing the other way in convincing one of my customers to switch to hydrogen from helium. The only exception is the analysis of hydrogen where argon is a great carrier but that is because most people do this with TCD rather than HID.

Best regards.

H>He>N>Ar in terms of separation quality

Dear DR,

I assume that, speaking of “separation qualityâ€

You can read this for some details:

http://www.chem.agilent.com/cag/cabu/carriergas.htm

As I know, of the 3 conventional gases N2, He & H2, nitrogen has the lowest HEPT at the optimum velocity.

Dear thohry,

I am sorry, but there is no theoretical foundation for

The Claim:

of the 3 conventional gases N2, He & H2, nitrogen has the lowest HEPT at the optimum velocity

and your source [1] does not provide a reliable experimental evidence for The Claim either.

A single graph of H vs. average velocity curves for N2, He & H2 in source [1] is an inaccurate reproduction of a similar graph of H.E.T.P. curves for the same three gases in a book [2] published by HP in 1979 (there were also 1981 and 1989 editions). In that HP book, the difference between the lowest H.E.T.P. for N2, He & H2 is less pronounced than it is in source [1]. More important is the fact that the difference is barely visible and is well within experimental error. Part of it was a known systematic error that skewed the measurements in favor of N2.

So, what do we have?

1. As far as I know, that single graph in HP book [2] is all we have to support The Claim. Only slight difference between the minima in the curves is visible in the graph. Other than that single graph, there is no other data in the book to support The Claim.

2. More than that. Because The Claim is in contradiction with theory, I made a significant effort to find experimental evidence reliably confirming The Claim. None other than that HP book [2] was found.

I would greatly appreciate any reliable experimental evidence of The Claim. Until such evidence is found, I invite all readers of these pages to assume that The Claim is just another URBAN LEGEND. (There are several of them in GC).

Respectfully,
lmb

Sources:
[1] http://www.chem.agilent.com/cag/cabu/carriergas.htm
[2] Rooney, T. A., "Theory of Chromatography", in: Freeman, R. R., High Resolution Gas Chromatography, Hewlett-Packard Co., 1979, pp. 7-21.

Something else to think about is that faster and narrower peaks give better detectability.

Peter

Imb, so all of us thousands of chromatographers that use H2 are masochistic ("H2 is dangerous", etc.) idiots? What is your explanation for the far inferior separation of LC as compared to GC?

Dear Hans,

I really don't think that lmb wanted to insult someone in his previous posts. As I understand, he was talking about the possible highest efficiency that anyone can achieve with different carrier gases and that the proper chosen linear velocity for any of the carrier gases used in GC can give you the same resolution on any sample (assuming use of the same column everytime). But as he stated, the run time for the same analysis (assuming that original resolution between peaks isn't changed) wouldn't be the same for the different carrier gases. The original resolution and the fastest time for one analysis you'll get with hydrogen and the same resolution but the longest time for the same analysis one will get with argon.

So I think that any chromatographer using H2 as a carrier gas isn't a masochistic idiot, since high speed analysis is what we all want to have/achieve, keeping the required resolution for the analytes throughout the chromatographic run.

Regards

Again I was braked out yesterday evening with "forbidden", trying once more:

I did not want to indicate that there was an insult involved, just wanted to emphasize how funny it appears to an old chemist to learn that all he had to do is multiply by a factor x, instead of going through the trouble to change from N2 to H2.
I am probably also wrong in my understanding that the formular for resolution is semi-quantitative at best. But then there is that statement by Imb:
„I assume that, speaking of “separation qualityâ€

Dear thohry,

I am sorry, but there is no theoretical foundation for

The Claim:

of the 3 conventional gases N2, He & H2, nitrogen has the lowest HEPT at the optimum velocity

and your source [1] does not provide a reliable experimental evidence for The Claim either.
.
.
Sources:
[1] http://www.chem.agilent.com/cag/cabu/carriergas.htm
[2] Rooney, T. A., "Theory of Chromatography", in: Freeman, R. R., High Resolution Gas Chromatography, Hewlett-Packard Co., 1979, pp. 7-21.

I got from the book " Chromatography today" by Colin F. Poole and Salwa K. Poole.
At the optimum, N2 has the lowest HEPT because its longitudinal diffusion is the lowest of all. The problem is N2's optimum is at rather low linear velocity compared to H2 or He, and it's narrow making it difficult to find the opt. velocity.

From my own observations over the years I would suggest that the "best" carrier is hydrogen. From the analytes I have looked at H2 has given better peak shape and seperation than both He and N2.
This does not mean that H2 is the best carrier in all circumstances, analysis is about achieving results that are fit for purpose.

GCguy

To HW Mueller

Imb, so all of us thousands of chromatographers that use H2 are masochistic ("H2 is dangerous", etc.) idiots?

Certainly I did not intend to insult anyone. More than that, I was glad to learn that there are “thousands of chromatographers that use H2â€

To lmb

1. In the Van Deemter equation, the longitunal diffusion contributes something into the HEPT does it.

2. From optimum, practically, we can shift upward (for shorter time) and the efficiency is lost the most in case of N2 (steeper), and that's the "more difficult" I mentioned.

As noted in an earlier post about making a comment and then getting their head well inside the trenches.... My only comment on this whole discussion is this: Who doesn't have to worry about total run time?

Best regards.