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H2 Carrier Gas question
Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.
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So our lab is considering making the move from He to on-demand H2 generation for carrier gas (He is becoming outrageously expensive and every third tank we get is contaminated). Does anyone have experience or recommendations for switching to H2 for GC-MS? Was looking at the Peak generators but they have yet to get back to me with a quote after two weeks (red flag). Would need to support two GC-MS systems (6890/5975 and 7890/5977) at once with one unit ideally. What kind of method adjustments need to be made when you change the carrier gas?
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Just search here or google that question about changes to expect when going to H2. It has been covered thoroughly.
In short, because the VanDeemter curves are a little different, your flow rates will have to change accordingly and the MSD will likely have its own issues when fed H2 instead of He. In the end, your costs and run times should go down and your separation efficiencies will go up a little.
In short, because the VanDeemter curves are a little different, your flow rates will have to change accordingly and the MSD will likely have its own issues when fed H2 instead of He. In the end, your costs and run times should go down and your separation efficiencies will go up a little.
Thanks,
DR
DR
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As far as chromatography goes, I think you'll adjust quickly to the H2. I personally prefer the H2 as a carrier. As far as ionization in a MSD, you may want to hook up a tank and run some tests. Passing EPA requirements for 8000 methods, tuning for BFB or DFTPP may be an issue. As DR noted, it's been discussed here in detail if you search the forums.
Regards,
Christian
Christian
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If not running EPA methods for compliance it is very good. Semivolatile EPA methods will pass tune for DFTPP without much problem, but Volatile methods are very difficult to pass for BFB tuning criteria on hydrogen.
In contrast to normal GC methods, you can't gain the benefits of increasing the carrier flow when switching to hydrogen since the vacuum systems have more difficulty pumping out hydrogen versus helium, with the exception of the oil diffusion pumps, but those are still limited to lower flows than turbo pumps.
You will have very high background when first switching, but it will clean up over time as the hydrogen scrubs out the flow path.
One word on the hydrogen generator, get one with the palladium membrane, the ones that use desiccant just don't remove enough moisture to be used as GC/MS carrier gas, we have one here now and I can't use it for GC/MS because the m/z 18 peak is almost as high as m/z 69 while m/z 28 is almost non existent.
In contrast to normal GC methods, you can't gain the benefits of increasing the carrier flow when switching to hydrogen since the vacuum systems have more difficulty pumping out hydrogen versus helium, with the exception of the oil diffusion pumps, but those are still limited to lower flows than turbo pumps.
You will have very high background when first switching, but it will clean up over time as the hydrogen scrubs out the flow path.
One word on the hydrogen generator, get one with the palladium membrane, the ones that use desiccant just don't remove enough moisture to be used as GC/MS carrier gas, we have one here now and I can't use it for GC/MS because the m/z 18 peak is almost as high as m/z 69 while m/z 28 is almost non existent.
The past is there to guide us into the future, not to dwell in.
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Passing EPA requirements for 8000 methods, tuning for BFB or DFTPP may be an issue.
If you are having problems passing BFB criteria for method 8260 when using hydrogen try 8260D. Most of the problems I've heard of were with too much 96.
4-BROMOFLUOROBENZENE (BFB) SUGGESTED CRITERIA*
m/z Intensity (relative abundance)
95 50 to 200% of mass 174
96 5 to 9% of m/z 95
(5 to 15% when using H2 carrier)
173 <2% of m/z 174
174 50 to 200% of mass 95
175 5 to 9% of m/z 174
176 95 to 105% of m/z 174
177 5 to 10% of m/z 176
* Criteria based on EPA Method 524.4 (Reference 17), with modified m/z 95 and m/z 174 abundance criteria
If you are having problems passing BFB criteria for method 8260 when using hydrogen try 8260D. Most of the problems I've heard of were with too much 96.
4-BROMOFLUOROBENZENE (BFB) SUGGESTED CRITERIA*
m/z Intensity (relative abundance)
95 50 to 200% of mass 174
96 5 to 9% of m/z 95
(5 to 15% when using H2 carrier)
173 <2% of m/z 174
174 50 to 200% of mass 95
175 5 to 9% of m/z 174
176 95 to 105% of m/z 174
177 5 to 10% of m/z 176
* Criteria based on EPA Method 524.4 (Reference 17), with modified m/z 95 and m/z 174 abundance criteria
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Ditto that 96 peak being high.
For 8260 a few of the delicate brominated and chlorinated compounds will have 25-50% less intensity but will be linear. Bromomethane will still stay under 2 ppb. Keeping the system extra clean will help.
Hydrogen will scour your whole system for organics. A trick the tech told me when first switching was to set the system on scan but drop the EV down to about 800. Then leave it scanning all night. That took care of cleaning up the source. I found the Agilent Link for He to H2 conversion.
We also got the larger diameter draw out lens and our 5973 already had the necessary stronger source magnet.
I use hydrogen as the carrier in my GC-FID and it works very well for doing DRO.
For 8260 a few of the delicate brominated and chlorinated compounds will have 25-50% less intensity but will be linear. Bromomethane will still stay under 2 ppb. Keeping the system extra clean will help.
Hydrogen will scour your whole system for organics. A trick the tech told me when first switching was to set the system on scan but drop the EV down to about 800. Then leave it scanning all night. That took care of cleaning up the source. I found the Agilent Link for He to H2 conversion.
We also got the larger diameter draw out lens and our 5973 already had the necessary stronger source magnet.
I use hydrogen as the carrier in my GC-FID and it works very well for doing DRO.
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Steve Reimer wrote:
Passing EPA requirements for 8000 methods, tuning for BFB or DFTPP may be an issue.
If you are having problems passing BFB criteria for method 8260 when using hydrogen try 8260D. Most of the problems I've heard of were with too much 96.
4-BROMOFLUOROBENZENE (BFB) SUGGESTED CRITERIA*
m/z Intensity (relative abundance)
95 50 to 200% of mass 174
96 5 to 9% of m/z 95
(5 to 15% when using H2 carrier)
173 <2% of m/z 174
174 50 to 200% of mass 95
175 5 to 9% of m/z 174
176 95 to 105% of m/z 174
177 5 to 10% of m/z 176
* Criteria based on EPA Method 524.4 (Reference 17), with modified m/z 95 and m/z 174 abundance criteria
That will definitely help, though at first even getting to 15% for 96 was difficult. After good cleaning and reduction of carrier flow to about 0.5ml/min I could hit 12% on the 5973, but you need a 40m x 0.18 column to have any head pressure at all when the run starts at 35C.
Our other problem here in Ky is they still don't recognize anything above 8260B
The past is there to guide us into the future, not to dwell in.
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Our other problem here in Ky is they still don't recognize anything above 8260B
Some states are still stuck in the last century. Is KY still hanging on at 524.2 for drinking water?
Some states are still stuck in the last century. Is KY still hanging on at 524.2 for drinking water?
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Steve Reimer wrote:
Our other problem here in Ky is they still don't recognize anything above 8260B
Some states are still stuck in the last century. Is KY still hanging on at 524.2 for drinking water?
For drinking water they allow the most recent updates, but the waste water and soil methods they wrote into legislation and they have to pass a new bill to amend it, which they never seem to want to do. It is just improper wording in the laws, should have said most current version of xxxx method. Some permit writers are ok with newer methods but some want to follow the law exactly as written.
We are currently moving to 525.3 for semivolatile drinking water and hope to move to 524.3 or possibly 524.4 so we can use nitrogen purge.
The past is there to guide us into the future, not to dwell in.
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Spoke with an Agilent tech about this and he said that it's not even an option for us because we have diffusion pumps and you need turbos for H2, so I guess we'll keep buying expensive contaminated helium for now.
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I was under the impression that diffusion pumps were better for H2 than turbos.
If nothing else, a turbo is certainly less efficient at pumping hydrogen than helium or heavier gasses.
The 5975 manual has a section specifically on using hydrogen, and nowhere in all of the safety precautions and how to(which get specific enough as telling you how much to tighten the analyzer door cover screws) as well as describing the pump-down procedure with H2 does it mention anything about the hi-vac pump type. Similarly, the sections on the diffusion pump don't mention anything one way or another about hydrogen.
If nothing else, a turbo is certainly less efficient at pumping hydrogen than helium or heavier gasses.
The 5975 manual has a section specifically on using hydrogen, and nowhere in all of the safety precautions and how to(which get specific enough as telling you how much to tighten the analyzer door cover screws) as well as describing the pump-down procedure with H2 does it mention anything about the hi-vac pump type. Similarly, the sections on the diffusion pump don't mention anything one way or another about hydrogen.
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I will second Ben's thoughts. I have used hydrogen with a 5973 that has a diffusion pump without problems. You may need to change the oil more often though as I don't know if there could be some hydrogenation of the oil at higher temperatures but otherwise it had better vacuum than the turbo I used hydrogen with.
Might want to send email directly to Agilent just to be certain.
Might want to send email directly to Agilent just to be certain.
The past is there to guide us into the future, not to dwell in.
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You could start the run at 1 ml/min and then drop down to 0.5 mL/min somewhere around toluene-d8 and pass the BFB while still having your head pressure at 35C.James_Ball wrote:Steve Reimer wrote:
Passing EPA requirements for 8000 methods, tuning for BFB or DFTPP may be an issue.
If you are having problems passing BFB criteria for method 8260 when using hydrogen try 8260D. Most of the problems I've heard of were with too much 96.
4-BROMOFLUOROBENZENE (BFB) SUGGESTED CRITERIA*
m/z Intensity (relative abundance)
95 50 to 200% of mass 174
96 5 to 9% of m/z 95
(5 to 15% when using H2 carrier)
173 <2% of m/z 174
174 50 to 200% of mass 95
175 5 to 9% of m/z 174
176 95 to 105% of m/z 174
177 5 to 10% of m/z 176
* Criteria based on EPA Method 524.4 (Reference 17), with modified m/z 95 and m/z 174 abundance criteria
That will definitely help, though at first even getting to 15% for 96 was difficult. After good cleaning and reduction of carrier flow to about 0.5ml/min I could hit 12% on the 5973, but you need a 40m x 0.18 column to have any head pressure at all when the run starts at 35C.
Our other problem here in Ky is they still don't recognize anything above 8260B
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