Chromatography Forum

By john acton on Thursday, August 5, 2004 - 03:59 am:

With the price of Helium getting more and more expensive, I am considering using hydrogen gas generator(s) to replace Helium for all my GC's with ECD,PFPD and the MSD detectors. I have been told that the hydrogen gas works with the Agilent MSD detectors in EI mode. Has anyone any experience or comments to make on using the generators as carrier gas. How many GCs can you run off a gas generator and are there sufficient safety features built in the generators to minimise a possibility of an explosion.

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By Consumer Products Guy on Thursday, August 5, 2004 - 08:08 am:

see http://www.chem.agilent.com/cfusion/faq ... =3&faq=400

Hydrogen as carrier gas is a bad choice for many semi volatile compounds. While it can promote homogeneous gas phase reactions its main adverse effect is due to liner activation through the reduction of metal oxides in the liner. This effect remains for a few hours even after switching back to He. These metal sites are detrimental to many pesticides, drugs and explosives.
If you wish please contact me directly for literature refecrences
Aviv Amirav
amirav@tau.ac.il

as said above, it could be some problems with H2 as carrier.
I worked with a Shimadzu H2 generator in essential oil analysis and it worked fine, but didn't use with MSD.

regards

DL

I thought I heard of a fairly recent serious explosion when using hydrogen as carrier for GC-MS - the explosion occuring within the MS itself. Has anyone else heard this?

I'm not using a MSD, but a different type of ms, but I think the same argument applies. The manufacturer of my ms has advised against the use of hydrogen because they do not like the idea of pumping hydrogen through the hot oil of the rough pump. This may be a safety risk.

As told by Agilent in a MSD course,the main problem with H2 as carrier gas is the possible accumulation in the MS chamber,if the vacuum pumps stop for any dysfunction.

Hydrogen can be used safely in a mass spectrometer. The possibility of any type of explosion is very small, and to have hydrogen explode in the mass spec itself is virtually impossible, as getting the proper mix of hydrogen and air in a vacuum chamber is extremely unlikely. Hydrogen is pumped more efficiently by a diffusion pump than a turbo pump, and people have encountered issues if the turbo pump does not have adequate pumping capacity to maintain a good vacuum, as the flow rate for hydrogen is generally higher than the rate for helium. The newer mass specs such as the Shimadzu 2010, Thermo DSQ, and Agilent 5973 with the performance turbo are better able to handle hydrogen as a carrier gas. All of these are quadrupole system, there are other issues with using hydogen in a ion trap that will usually cause problems. I have not heard of hydrogen passing through the rough pump oil being an issue, and with the typical flow rate into a mass spec at 1 to 2 mL/min there is really not enough hydrogen going into the pump to cause much problem.

The main issue I would worry about with the use of hydrogen gas is the purity of gas coming from a gas generator. The detectors you mention are all high sensitivitly detectors and require very high purity of gases for proper operation.

Can anyone tell what are lab safety requirements for using hydrogen as carrier gas for GC-MS?

Most of the carrier gas flow (depending on the split ratio) come out of inlet vent, not into the MS, so if there is some chance of explosion, it should be in the lab, not inside the MS. To avoid the problem, a plastic tubing can be used to connect the inlet vent in to the hood. Hydrogen is a better carrier gas as far as chromtography is concerned, it should worh ok in GC/quadrapole MS, the spectrum of the mother ion after CID are a little diffrent from helium in GC/Ion trap MS/MS.

As an ex Thermo GC/MS salesman we were always told that the only reason Hydrogen was not suitable was that the sensitivity of the system reduced by about an order of magnitude. The reason given was that the Helium takes part in the ionisation in both EI and CI and Hydrogen was less efficient in the reaction.

Helium is one of the inert gases, and it's a one-atom molecule, I'm not sure about CI mode, but in EI mode it shouldn't affect ionization efficiency. On the other hand, it's possible for hydrogen to react with the ions, especially in MS/MS.

Can anyone tell what are lab safety requirements for using hydrogen as carrier gas for GC-MS?

I'm not sure about teh MSD related specifics, but if you have a detector set up to cut H2 flow in the event of a leak and/or making sure that you have nothing more than magnetic catches on any chamber doors, you'll be off to a good start. Frequent leak checks would also be a good thing to add to the routine.

As to H2 use in general, at least for FIDs, the VanDeemter (sp?) plots are superior for H2 as a carrier (better than He, way better than N2 or Ar etc.).

The use of hydrogen instead of helium would have a large effect on the performance of an ion trap, so that could be the origin of the advice at Thermo not to use hydrogen. I know that ion traps work best with about a mL/min helium flow.

There could well be a role for the carrier gas in the ionization process. With 70 eV ionization there will definitely be ionization of some of the carrier gas molecules. I have never seen any data on the use of diffeent carrier gases and the effects on ionization, but one time I tried to run some samples on an instrument which had been connected to nitrogen instead of helium. If you want to see some really weird mass spectra from a quadrupole instrument just try running with nitrogen carrier gas. Might be a nice thesis for a graduate student interested in chromatography.