Chromatography Forum

I have been developing methods on nitrogen as a carrier for 6 months. Analyticly imperfect, yes. We largely compare quality of incoming indutrial chemicals and validate finished products. In this environment nitrogen works, and is cheap. I have built up switch valves to allow me to revert to He for new analyis but always leave a column flow of N2 when not using the GCs.
This is strted as a $ sving project, nitrogn carrier while GCs were idling/not in use. Still validating some of the ISO 9000 QA methods but have reduced He usage 80%.

Argon may be a replacement for some inert gas applications since it is readily available as almost 1% of the atmosphere.

For the same peak capacity, hydrogen is about 70% faster than helium in GC-MS applications and in high peak capacity applications. Hydrogen is about 25% faster than helium in low peak capacity non-GC-MS applications. And higher speed typically comes with lower (better detection limits). This suggests that, if shorter analysis time and/or lower detection limit are important, hydrogen carrier gas is the best choice.

However, if cost rather than speed and detection limit are the main reason for switching from helium then other considerations might be important.

Nitrogen is cheaper than helium. Unfortunately, in GC-MS applications and in high peak capacity applications, nitrogen is almost two times slower than helium and three times slower than hydrogen. In low peak capacity non-GC-MS applications, nitrogen is 3.3 times slower than helium and 4 times slower than hydrogen. And, of course, lower speed typically comes with higher (worse) detection limits.

Argon is just slightly slower than nitrogen.

The bottom line appears to be this: If analysis time and/or detection limit are not the issues then switching from helium to nitrogen or to argon is worth considering, especially if the safety issues related to hydrogen should be considered.

Would there be any point using argon instead of nitrogen, provided it's the right grade (I'd use scrubbers on everything anyway)?

It depends upon the type of detector you are using.

ECD vs FID

Argon ionization Detector vs FID

TCD vs FID

MSD, etc

Just a note on Cell degeneration. Cell degeneration has a lot to do wit the efficiency of the electronics, polymer used and the heat generated inside the cabinet. Heat can quickly deteriorate the cell. Some companies have to use ~3v to generate H2 and over just over 1V. The lower the power, the more efficient the system is and the less heat generated.

We have 10 GCs running H2 now, 20 columns and 4 are FID with one NPD and all are running off one 800ml/min hydrogen generator. I noticed a while back that we were down to 24psi on the line with the generator running at 103% capacity. My GC analyst was telling me we should not be near the capacity after figuring in his flow rates, but he forgot that if you were running 3ml/min column with 20:1 split after a splitless injection you were using 60ml/minute per column.

Our generator is 4 years old and we really haven't had any problems out of it yet other than I believe exceeding its capacity. With our setup we made back the price of the generator in less than two years and if we have to replace the cell this year or next we will still come out ahead on cost versus that of cylinders(especially considering what used to be on Helium that was switched over). We will probably trade up to a 12ml/min generator or add a second 800ml/min unit. I am pushing for adding the second more for redundancy than flow as we could limp by with shutting down a few units if needed if one generator is offline for a while. We also have hydrogen tanks at the other end of our supply lines outside just in case of power outages like when we were out for 8 days after an ice storm a few years ago. Easy to set up if you set the tank regulator a few psi lower than what the generator is running with a back flow preventer in line it will kick in once the generator stops.

... We also have hydrogen tanks at the other end of our supply lines outside just in case of power outages like when we were out for 8 days after an ice storm a few years ago. Easy to set up if you set the tank regulator a few psi lower than what the generator is running with a back flow preventer in line it will kick in once the generator stops.

James, I can't see a point of doubling hydrogen supply system for emergency situations like power outages. Are your GCs battery operated ?

... We also have hydrogen tanks at the other end of our supply lines outside just in case of power outages like when we were out for 8 days after an ice storm a few years ago. Easy to set up if you set the tank regulator a few psi lower than what the generator is running with a back flow preventer in line it will kick in once the generator stops.

James, I can't see a point of doubling hydrogen supply system for emergency situations like power outages. Are your GCs battery operated ?

I don't know about James, but I have battery operated GCs - the batteries are in a 6KVA UPS.

Peter

... We also have hydrogen tanks at the other end of our supply lines outside just in case of power outages like when we were out for 8 days after an ice storm a few years ago. Easy to set up if you set the tank regulator a few psi lower than what the generator is running with a back flow preventer in line it will kick in once the generator stops.

James, I can't see a point of doubling hydrogen supply system for emergency situations like power outages. Are your GCs battery operated ?

We have UPS on a few but mostly it is to keep a flow for the older ones with mechanical flow controllers if power interrupts the generator. The generator has a power backup but it will only last a few minutes, if the power is off overnight then it is better to have some flow through those columns than non at all.

We are currently installing a natural gas powered backup generator so hopefully those few minutes of backup will be enough to bring it online.

As for doubling the capacity, we need a little of it for expansion and the second unit would be preferred in case the first unit loses a cell or something. That would allow us to run at least some of our GCs until it can be repaired.

Where I once worked the need to continue operations was of foremost importance. Having a backup or immediate replacement is surely dependent upon the nature of the work which you do.

There is no single best proposition, but the sharing of criteria can be insightful.

Mission critical situations, where a loss of throughput could cost manifold the cost of a backup hydrogen generator or the storage of a few cylinders of hydrogen with regulation, necessitate a different philosophy from that of a small research lab where a few days of down time is no big thing.

I found a GC battery power backup of 6000 VA fascinating. What a lab that is !

best wishes,

Rod

...
I don't know about James, but I have battery operated GCs - the batteries are in a 6KVA UPS.

Peter

What is the hold up time of this UPS in your typical load configuration ?

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edit: Sorry, the question was about back up time, not hold up time.

I found a GC battery power backup of 6000 VA fascinating. What a lab that is !

best wishes,

Rod

Hi Rod

It's the Paul G Allen Family Foundation Laboratory for Wildlife Chemistry, In Maun, Botswana. The 6KVA backs up power to 3 GCs, one with an MS, and associated computers etc. Apparently for worse case power drain (all the ovens programming at full blast) I should have 12 KVA. The UPS bridges the time between the mains power going off and the backup generator kicking in, and it also cleans up the incoming mains power. Lately we have been getting power cuts of a few hours once or twice a week.

Peter