Hydrogen carrier gas and GC/MS

[littlepeaks]

I have been running hydrogen carrier gas for years on my instrument doing analysis by NCI. My "buddy" decided to tap off the gas line and try running on his instrument using hydrogen (he has an Agilent 5973 running in the EI mode. Background is awful for him and the baseline is nasty. I know that hydrogen tends to scour all the contamination out of the gas lines, but his has been hooked up for 5 days now. I know that using NCI, I don't see all that garbage (I do nasty stuff like sediments, fish tissue, lichens, etc., and there's a lot of stuff I don't see). We are using a gas cylinder as a source. My buddy talked about buying a "catalyst" to put in the gas line to clean it up, but they supposedly cost about $8,000.

Any tips on using hydrogen for GC/MS would be appreciated.

--littlepeaks (at the National Peak Integration Facility )

[Peter Apps]

I have never heard of hydrogen scouring contamination out of gas lines (although heating copper to red heat with hydrogen flowing through it does a very good cleaning job I doubt that this applies to what your colleague is doing).

Hydrogen is reactive in an ion source though, and there is a lot of material in the forum archives on just this issue - try a search.

The "catalyst" is probably one of many options for making sure that the carrier gas is pure when it enters the intrument (although the price seems a bit high) , and you should certainly have some kind of gas scrubber in place no matter what gas you are using. NB that purifiers are often specific to a certain gas.

Peter

[Don_Hilton]

Where did your buddy find the tubing to hook up to the hydrogen line? Tubing that is not new GC grade tubing is immediately ssuspect. I've even seen what was presumed to be new GC grade tubing that was not clean. Oils and other garbage in poor grade tubing or tubing that has been around the lab and used for other purposes may take a long time to migrate out of the tubing. (We are talking years, perhaps decades.)

[littlepeaks]

He said the tubing was new "GC Grade" tubing. We keep a big roll around here for those purposes because we're always hooking up stuff. He decided to take the tubing down and solvent rinse it, and then purged it with gas. We'll see if it makes any difference.

BTW the gas is UHP Grade Hydrogen. Everyone was of the opinion that it should be sufficient for that purpose. Another person suggested we move the tank directly in back of his instrument and hook it up temporarily with teflon tubing, which he thought would be cleaner, but more porous, so we wouldn't want to use that as a long term solution.

Thanks for all the tips. I did do a search on the forum, and though I found another thread on this subject, I don't think anything new was suggested.

[Don_Hilton]

I would suggest not using teflon tubing to hook up a GC. Expect the tubing to have plasticizers in it, particulary if it has sufficient wall thickness to hold pressure and is flexible. And, yes teflon is porous - and will allow oxygen to diffuse into the gas stream as well as allowing hydrogen to diffuse out of the gas stream. With a sort, sturdy lenght of tubing, I doubt that you would have sufficient diffusion for a safety concern, but probably enough diffusion to have a concern about the life of the column.

[thohry]

I have tried once to use H2 as carrier gas for a GC/MS. The H2 was from a UHP Generator using palladium membrane and it claimed that the gas is of 99.999%. But the baseline is very noisy so we had to switch to normal He cylinders.

[jh1]

When we hooked up one of our GC/MS systems to hydrogen as a carrier gas we used new copper tubing that had been purged with hydrogen, even then Agilent suggested running gas through the lines for 2 weeks before turning the instrument on to blow out any residual junk.

Oh and even after all of this the baseline while not horrible has always been significantly more noisy than the same system using Helium.

[littlepeaks]

Well, I could only get the chromatographer, who is trying to set this system up, to clean the end of the gas line (whatever that means). I personally don't have time to mess with it right now. I don't know how you guys feel about this, but I suggested he remove the tubing, fill the tubing with nitrogen, put the end caps on, and shove the whole thing in an oven overnight (we use the huge oven for baking glassware overnight to remove all organic contaminants). The tubing is about 25 feet long. I think the tubing should be able to withstand the pressure, and if there was air inside instead, I don't know how oxidation products would affect the gas quality.

[Don_Hilton]

If you heat the sealed tube with contaminants in it - where are they going to go? They will either decompose into something else or they will condense on the tubing when it cools.

I've known people to heat the tubing with a heat gun with innert gas sweeping out the tubing. I've taken tubing and rinsed it with a series of solvents, finishing by blowing the tubing dry with some heat applied.

[Peter Apps]

Although it is not possible to rule out a dirty section of tubing as the cause of the problem there is no reason to believe that dirt will bleed off into hydrogen any more than it does into any other gas.

The underlying reason that you get noise when you use hydrogen in an MS with an EI source is that the hydrogen itself gets ionised. If you had searched the archives you would have found a lot of useful discussion on exactly this problem, and saved yourself and your colleague some time.

Peter