Helium Carrier Gas Purity

[sdegrace]

Hi folks,

I was hoping to get some general reaction on the topic of the quality of helium carrier gas. The market for helium just seems to get tighter and more expensive, so if one is unhappy with one's supplier, I don't think there is a lot of recourse, you just have to work with whatever you can get.

I'm interested in knowing if people have observed any significant variability in the quality of the helium they are purchasing of a particular grade from a particular supplier, and what extra measures most people are taking to clean up the helium they are buying? Also, does anyone have any opinion on the UOP mat/sen purifier from Superco (p/n 22680U for the one with 1/8" fittings).

We have been buying helium with a label claim of 99.999% purity and using it as-is for purely FID applications and have had no problems, but recently I've become somewhat suspicious of it due to problems with getting consistent and stable baselines when running the temperature program with no injection (when the column is not connected to the detector, the same experiment results in the expected little or no change from a stable, flat baseline), and I plan to try the above purifier. I'm hoping to gain some benefit from other people's experience.

Thanks,

Stephen

[skunked_once]

Our gas supplier here in the midwestern US is Praxair and I have had no apparent problems with the helium, air, and hydrogen that we use for the FIDs. We use 99.995% helium and a molecular sieve cartridge to trap moisture. This may be overkill for FID but after the molecular sieve trap, we use the Supelco High Purity Gas Purifier (#23800-U). I have found that removing oxygen from the carrier gas is important for long column life. We once had a Hewlett-Packard electron-capture detector in the 80's that was very sensitive to oxygen in the carrier gas. Without an oxygen trap, the ECD baseline would rise quickly off scale during gradient programs. This was probably due to decomposition of the column stationary phase in the presence of oxygen.

[tigerk2001]

For my part, I'm based in north America and normally deal with LINDE(BOC) and Praxair for Helium 5N.
For most of the time, I didn't get any problem, but time to time I got a contaminated cylinder with unusual air content what makes my FID's and DID's being unstable like you.
I now developped my own gas purifier with dual stage vessel for removal below 1ppb impurity (H2-O2-N2-CH4-NMHC,H2O,CO-CO2) with intelligent auto-diagnostic and easy interchangeable getter, which is now one of my standard product in 1/8''& 1/4'' compression or 1/8'' & 1/4''vcr in and out.
If you are interested to evaluate it and get a unit, you can get in contact with me and I'll send to you the litterature about it.
You can email me at instrumentseoul@gmail.com and I will come back to you shortly with all details and pricing.


thanks

[AICMM]

sdegrace,

In the recent past I have found helium with oxygen in it, kind of odd since the CGA fittings are different, and helium with argon in it, much more understandable. Both were found when looking at the tune on the MS. Both by themselves (that is, no nitrogen to go with the oxygen for example.) Both at pretty low levels but still they should not have been there. In the case of the oxygen, the helium was in a six pack, in the case of the argon it was in a single cylinder.

So, yes, there are issues sometimes. Filters for water are a must, filters for oxygen are, in my opinion, much more application specific (anything really high temp. for example.)

Regarding the heated getters, my only experience was that as it aged it caused an ECD to go wild. When removed the ECD was fine. That was quite a troubleshooting chore on the part of the fellow who found it.

Best regards.

[Ron]

In the past, 4 9s helium cylinders and 5 9s helium cylinders were filled from the same supply, the difference was that each 5 9s cylinder was individually analyzed and cerified. I not sure if the same held true for higher puritiies, but it may have.

I suspect that more people are running the cylinders closer to empty insteads of replacing them with 300 to 500 psi left in the tank. Lowering the tank pressure increases the possibility of infiltration of air into the cylinder, so unless the cylinders are individually tested the possibility of lower purity gas is greater.

To sum up, even if you are buying the same grade helium you have always bought the chances of getting a bad cylinder is higher than before, unless the indivilual cylinder is tested and certified.

[Bruce Hamilton]

I suspect that more people are running the cylinders closer to empty insteads of replacing them with 300 to 500 psi left in the tank. Lowering the tank pressure increases the possibility of infiltration of air into the cylinder, so unless the cylinders are individually tested the possibility of lower purity gas is greater.

To sum up, even if you are buying the same grade helium you have always bought the chances of getting a bad cylinder is higher than before, unless the indivilual cylinder is tested and certified.

Here, the main gas supplier, BOC, now has cylinder valves incorporating a check valve that doen't allow the cylinder to drop below a certain pressure or backflow. Customers aren't charged for that gas, and it doesn't show on their gauges. They have been retrofitting them ( valve has a slightly larger body ) over the past 5 years or so.

I would say that, for NZ anyway, the possibility of contaminated gas is lower than it was a decade ago.

For a couple of decades I used technical grade He and H2 from a purgeable manifold with a purifier chain of Alltech ( now Grace ) Drierite/Molecular sieve, large Oxy-trap, indicating oxy-trap, Activated Carbon that was kept pressurised 24/7.

Worked fine for most applications, and the train usually only required an annual regeneration, unless a dodgy cylinder was hooked up.

Please keep having fun,

Bruce Hamilton

[Omaejel]

We generally get our helium by trailer load. We just turn on the valves on the trailer as we run low. It's really nice. But we recently got in a trailer of helium that seemed to be contaminated with water. We had 16 mass specs that all had a ton of water in them. It took us a little while to figure out the problem because we noticed after one was cleaned and just never could get all the water out! then we did some checking on the others and discovered the problem was everywhere. We had a new trailer brought in and installed filters.

Has anyone had any luck running nitrogen as a purge gas when running VOC's? We tried that here but didn't have a lot of luck with it. It just didn't seem to get as good response and the calibrations never seemed to work as well.