Hello folks, I have a friend that works in an environmental lab analyzing pest/herb/pcb conginers etc.. he has been doing this for 10+years, he said he is modifying the EPA methods tweeking conditions to optimize seperation. he rescently told me how he is using hydrogen as a carrior gas in is gc/fid system. My first thought was that the reasoning behind helium is that it is inert. Helium is running out(let say only a limited supply exists) and due to this fact it can be very costly. Taking this into account he has begun to experiment with hydrogen.Can anyone explain the chemical rational behind this or has anyone heard of such a thing?
By Anonymous on Friday, February 16, 2001 - 05:06 am:
Hydrogen is a very good carrier gas. The optimum linear velocity is about 40 cm/sec. Therefore, it allows maximum resolution in about half the time of helium. Safeguards should be in place to prevent a buildup of H2 in case of an FID flameout, leak or MS vacuum pump failure. Also, changes in mass spectra have sometimes been seen with environmental compounds.
By David McCalley on Friday, February 16, 2001 - 05:29 am:
I agree with what anonymous says. The optimum carrier gas flow velocity lies at higher flow than for helium. I only once experienced a problem which I thought MIGHT be due to hydrogenation of double bonds in my sample. It seems that hydrogen is surprisingly unreactive when oxygen is excluded-as is hopefully the case in a GC column, at least at normal GC temperatures. I would stress the importance of a leak detector and automatic shutdown mechanism in case of a leak or column breakage. Otherwise, you can end up with a sealed column oven full of hydrogen, which together with the heating element can give rise to a serious explosion.
By Bill Jenko on Saturday, February 17, 2001 - 10:39 pm:
I agree with all that annonymous and Mr. McCalley say, but I think they may exagerate the danger of H2 carrier a bit. Helium is rarely used in Europe; Hydrogen is routinely used safely. In 30 years of doing GC, I've heard of only one GC that exploded due to an accumulation of H2 in the oven from the carrier, and that was in a process GC without proper oven ventillation, due to a very bizarre series of events involving both a massive carrier leak and a faulty oven heater. If you get your H2 carrier from a cylinder, or even 2 cylinders manifolded togeter, it is really hard to reach the LEL of H2 in a well-ventillated lab GC oven, or a well-ventillated room. Obviously, check for leaks. Shut off the carrier whenever the GC is not turned on, with the fan off. If you have a combustible gas alarm, or a portable leak detector, putting the sensor near the oven exhaust is a nice idea. Vent the injector vent (split vent, if any) outside or up a fume hood. If you get your carrier H2 from a large "house" system, or from a bank of many cylinders, consider a "flow fuse" (Autoflow Co., or Melema Engineering)which is an adjustable trip valve that closes on high flow. You can put this devise on the main header supplying the H2, or one at each GC if you prefer, but they are not cheap($500-900 each). With reasonable and inexpensive precautions, H2 is a very safe GC carrier.
By Anonymous on Sunday, February 18, 2001 - 12:48 pm:
I do know of someone who plumbed H2 into a GC he was setting up by mistake (meant to use He). He blew the door right off the instrument. The lesson--always verify the source of your lines the first time you use them.
By Terry Daigle on Tuesday, April 24, 2001 - 05:31 pm:
WE've been using H2 as a carrier for over 20 years for compositional analysis of crude and natural gas. We've never incurred an incident yet.
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