using hydrogen gas with GC/MS

[RioRita]

Has anyone used hydrogen gas routinely with GC/MS? What are the benefits? What are the concerns?

[Don_Hilton]

Hydrogen can result in a reduction in sensitivity and has been known to result in dehalogenation of chlorinated compunds in the ion source. The capability to run faster chromatography remains.

[thohry]

Has anyone used hydrogen gas routinely with GC/MS? What are the benefits? What are the concerns?

I once tried to use H2 as carrier gas in GC/MS. The H2 is from a generator (with spec of 99.999 purity). The baseline was much worst than that if He is used so I stopped thinking about that.

[Peter Apps]

I have heard that hydrogen can hydrogenate double bonds during ionisation. There is a possibility that if the pump is off the MS fills up with hydrogen which could subsequently explode.

Peter

[jh1]

The biggest benefit of course is the decreased cost vs. purchasing Helium. Otherwise you can also reduced your run time by about half while still having similar separation and detection limits.

Downsides: The baseline is typically much nosier and air leaks tend to be larger and harder to track down. You also have the safety issues involved, which can be numerous.

[mtorrey]

I have never used H2 for a carrier gas but the biggest advantage is speed, use higher velocities. Must have clean system. If system not clean have high backgrounds. Must have pure carrier gas grade hydrogen.

The safety issue is overblown. Hydrogen is extremely diffusive in air and difficult to reach an explosive level of ~4 %. Most GC's flow regulated with safety shutdown and some have explosion proof doors.

That said we still use He because to change all our methods to use H2 is too much bother.

Mike

[lmh]

aren't there issues about the vacuum pump?

[mtorrey]

aren't there issues about the vacuum pump?

All about hydrogen safety:

http://www.chem.agilent.com/cag/servsup ... afety.html

Mike

[JI2002]

If your work is under the regulation of EPA, you are likely to have problems to pass the BFB tune or DFTPP tune. My experience was that ratio of ion m/z 96 to ion m/z 95 was a higher than the criterion in BFB tune.

[gpronger]

Rio,

Much of the reason you're getting ambiguous answers is that the correct answer is the fairly almost useless answer of "Depends".

First, as mentioned is that when you switch from He to H2, you're flow rate will go up fairly significantly, so the question is whether or not you're pumping system is capable of handling the increased flow.

Second, one of the mentioned points was possible reaction (basically CI using hydrogen) with you're analytes. There are (at least) two causes of this with H2, the first is simply if you're vacuum system is not keeping up (source pressure high with a reactive gas) or the configuration of the source. Some sources, even for EI, are fairly "closed" in design. With these, almost regardless of the overall source pressure, the localized pressure (within the source) can be high enough to get some level of CI going.

If I was in your shoes, the first thing I would do is talk to the manufacturer. If I got a non-answer from them, I'd first look at the flow rate spec for my vacuum system and compare it to what I'd likely see with H2. If this was inline, then I'd simply try it.

Greg

[Ron]

Most benchtop GCMS systems will not work too well with hydrogen due to the higher flow rates and reduced pumping efficiency of hydrogen compared to helium. If you go to a narrower bore column, say a 0.20 mm id instead of a 0.25 mm id you will be using a lower flow rate and are less likely to overwhelm the vacuum system.

There is a sensitivity reduction in using hydrogen, as several of the posts above have pointed out the baseline is noisier, so the signal to noise ratio is decreased. In many cases this is not that important because the samples are high enough in concentration that the instrument is not operating anywhere close to the detection limit.

Reaction of compounds in a mass spec with adequate pumping capacily to handle hydrogen carrier is rare, but possible. Most compounds will show little if any change in mass spectra going from hydrogen to helium if you do an autotune that adjusts mass pattern.

Finally, it is very difficult to blow up a GC or a mass spec with hydrogen. It is very hard to find a verifiable story involving a hydrogen explosion in a GC, and in most cases that the explosion can be verified it happened on an old packed column system 20 or 30 years ago.

[gpronger]

Are you saying that the only verified cases were with instruments that were 20 - 30 years old? I've had a few chemists who would consider that an option to get rid of a 20 - 30 year old instrument. ;>

[Ron]

No, the only cases that I know of where the person telling me the story had information that lead me to believe the story was true (including location, the names of people involved, and details of what happened) occurred 20 or 30 years ago.

[CE Instruments]

I know of a GC Hydrogen explosion from around 18 years ago with a Capillary system. The operator installed the column without ferrules On leaving the GC, the column no doubt fell out and the GC filled with Hydrogen before going bang Fortunately , no-one was hurt, the GC after an engineer check still worked but was a little rounder than before

Hydrogen diffuses fast so accidents are rare. Modern GC systems use Electronic flow controls which will cut out if the back pressure is removed adding another level of safety. Use of a low capacity Hydrogen generator also cuts the risk. All the manufacturers will recommend a Hydrogen detector for safety, these can be added later to any GC for a cost of between £1-2K (UK price installed)
Unless anyone knows better this appears to be the only supplier world wide and is re-badged for Thermo and Agilent systems.

H2 9000 pdf

[labassist]

99.999% purity is not carrier-grade which caused your baseline issues. Hydrogen generators are available to produce 99.99999%