GC carrier gas change from helium to hydrogen

Discussions about GC and other "gas phase" separation techniques.

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Hi , I'd be interested to hear any views on adapting GC methods from helium to hydrogen as carrier gas. We use both MS and FID detectors. I understand there might be some loss of sensitivity with MS, but I've tested some dilutions and I think we'll be OK with that. I think with hydrogen the number of theoretical plates is increased, so would it be reasonable to expect faster run times and improved resolution? Any thoughts or comments most welcome.
For the FID you can increase the flow rate and have better separation and peak shapes with hydrogen which will increase productivity. With MS you can't increase the flow rate without overloading the vacuum system, you actually need to lower the flow rate a little, but you still gain linear velocity, though it is not at the optimum suggested by the van Deemter plots. Also if you must meet a tuning criteria for Bromofluorobenzene for EPA methods it is difficult if not impossible with hydrogen, DFTPP is easy to meet tune criteria though. Doing MS with hydrogen will give you less expensive carrier gas especially when using a gas generator, but will keep the run times and separation about the same as helium.
The past is there to guide us into the future, not to dwell in.
I can't speak for MS regarding Hydrogen carrier, but I have converted several GCs over from Helium to Hydrogen carrier.

We get much sharper peaks, faster run times, and the cost savings too. Keep in mind, when switching over, not only do you have to increase the column flow, but you will have to speed up the column oven temperature profile to experience the most comprehensive benefits in decreased analysis time.

Easiest to use one of the method translation programs out there to get you started. I highly recommend the switch over for GC applications.
"Also if you must meet a tuning criteria for Bromofluorobenzene for EPA methods it is difficult if not impossible with hydrogen, DFTPP is easy to meet tune criteria though."

Soon to be released 8260D addresses this.
https://www.epa.gov/hw-sw846/validated- ... ectrometry

The other problem that has been observed is inlet reactivity when using chlorinated solvents, especially DCM. Not everyone sees it but in at least one instance it has ruined an inlet. Check with your instrument manufacturer for recommendations. I know both Agilent and Thermo have presentations on this.
I converted two GCs to use hydrogen carrier, with nitrogen as the make up gas. Worked fine, and yes methods needed to be adjusted.

Boss had seen newsreels of the Hindenburg, so he wrote special SOP where we had to use electronic leak check and document in the binder EVERY TIME we changed the septum or the inlet liner.

Agilent has a good video of actually trying to make a GC explode, and even that wasn't that easy. And the GC still worked after that.
KM-USA wrote:

Boss had seen newsreels of the Hindenburg, so he wrote special SOP where we had to use electronic leak check and document in the binder EVERY TIME we changed the septum or the inlet liner.



I should have thought that you would be logging a liner or septum change anyway, and would be checking for leaks anyway, so ticking a leak check box is pretty close to the easy end of the spectrum of QC measures.

Peter
Peter Apps
When changing from He to H2, you should not expect any improvement in the resolution. The only case when the resolution improvement is possible, it is when the improvement is possible with both gases, i.e. when the original analysis with He was not optimized for the best resolution. The key here is that carrier gas does not affect the best possible resolution.

What's good about H2 is that it is the fastest carrier gas.

In a method translated from He to H2, the flow rate of H2 should be 25% higher than was the flow rate of He. The temperature program should be translated accordingly (see below). The exact changes in GC-MS are different from those in GC-FID. The former ones are easier to predict.

GC-MS: Method translation from He to H2 reduces the analysis time by 40%. In a temperature-programmed analysis, the hold-time for each temperature should be reduced by 40%, and each heating rate should be increased by 68% (as 1/0.6 = 1.667). That's all.

The changes in GC-FID are more difficult to predict in the short note like this because they depend on column diameter and length. Method translation from He to H2 reduces the analysis time by 20% to 40%. To figure out the changes in the temperature program, you can use a GC Method Translation freeware available on line (see below), or do the following. (a) Measure the void time (tMHe) in the original analysis with He. (b) Measure the void time (tMH2) in analysis with H2. (c) Calculate the time reduction factor (TRF) as TRF = tMH2/tMHe. (d) Calculate the time (tHoldH2) of each temperature-hold in the method with H2 as tHoldH2 = TRF*tHoldHe (tHoldHe = temperature-hold time with He). (e) Calculate each heating rate (RateH2) in analysis with H2 as RateH2 = RateHe/TRF.

OR, to translate any method (GC-MS, GC-FID, etc.) get GC Method Translation freeware. I think that http://www.restek.com/ezgc-mtfc is the best. In the "Results" choose "Solve for" = "Translate". You can also try "Solve for" = "Speed". Most likely, it will recommend the parameters for the best resolution-speed tradeoff. Don't use "Solve for" = "Efficiency". This option is practically worthless, and should not be there.

Additional comment. If the extra-column peak broadening in your system is significant (due to insufficiently sharp sample introduction, insufficiently fast detector, etc.) then switching from helium to hydrogen might cause some loss in the resolution because the faster is the analysis the more sensitive it is to the extra-column peak broadening.
These are true if you want to get the most out of the switch efficiency wise. But you can also change to hydrogen and leave the flow and temperature program nearly the same and get close to the same retention times you had with helium. It does not gain you anything in time savings, but it will gain you saving in gas costs if you are using a generator.
The past is there to guide us into the future, not to dwell in.
I've done it for a 6890/5873 and a 6890/FID. The FID run is over in 20 minutes for DRO. DRO is finished in 15 minutes but I leave the temperature up for another 5 minutes to elute any heavier compounds.

On the 6890/5973 get a larger diameter draw out lens to improve linearity. I think its a 9mm hole instead of 6mm. The newest systems already have the larger holes. Whole system must be very clean. Hydrogen is an active gas scavages junk all along its pathway. BFB will be difficult to pass on the 95/96 ratio but it can be done if the system is clean. We had some trouble with some of the more easily broken down compounds such as bromoform (see below). We got consistant recovery but signal was lower than with helium.

Make sure you are purging with an inert gas, not hydrogen. I was purging with Argon (had a dewar for the ICP-MS might as well use it) on my archon autosampler and using hydrogen in my Tekmar 3000 to dry purge away the argon. I figured, this kept the argon out of my MS (it quenches signal) and no sudden gas changes during desorption. However, I recently stopped using argon for purging and hydrogen for dry purging, switching to nitrogen for both; and immediately got 50-100% larger recovery increases for dibromochloromethane, bromoform, and 1,2-DBCB. This illustrates that Hydrogen does affect the easily attached compounds during desorb. I imagine the effect would be less if the trap were not saturated with hydrogen gas prior to the desorption cycle.
steve wileman wrote:
Hi , I'd be interested to hear any views on adapting GC methods from helium to hydrogen as carrier gas. We use both MS and FID detectors. I understand there might be some loss of sensitivity with MS, but I've tested some dilutions and I think we'll be OK with that. I think with hydrogen the number of theoretical plates is increased, so would it be reasonable to expect faster run times and improved resolution? Any thoughts or comments most welcome.


In my experience translating He to H2 chromatography methods, the main advantage is run time. Theoretically you do get better resolution, but the difference is incredibly subtle and did not *effectively* improve the resolution we got even between n-alkanes on a non-polar column, which is about as favorable an environment for H2 chromatography as you can get.

I did not transition our GC-MS instrument from He to H2 due to the better quality of mass spectra available in the library I had at the time. However, I was attempting to quantify hydrocarbon mixtures with 100+ compounds, many of which were of indeterminate identity prior to our analysis. Having clear mass spectra to compare to our library was important, as we did not have the resources to analyze hundreds of individual standards. If you use H2 in GC-MS, you have to account for the +1 ions and fragments. This is reasonably simple if you are only analyzing a specific set of known compounds for which you can generate your own mass spectra.

TL:DR, GC-FID: use hydrogen, expect faster analyses, don't expect seriously improved resolution. For GC-MS, it depends on the application and your need for sample throughput increase.
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