Chromatography Forum

Good morning, all.

I'm planning on redoing the gas lines for my GC-MS, since I am set to acquire a new, but used, GC from one of our production facilities. I'm planning on swapping over from helium to hydrogen at the same time. Currently, the helium passes through a series of gas filters before making their way to the GC, but the filters haven't been changed before I started working at the facility. I find them unnecessary, since we buy ultra-high pure gases, but I'm curious on the consensus of the rest of you.

Do you buy high purity carrier gas and do you have filters in addition? How often are your filters changed? Is this done for any specific reason or simply policy?

I look forward to your responses.

I buy five nines gas because 6 nines is too expensive, and I have scrubbers immediately upstream of the instruments because what comes out of the end of the pipe is not as pure as what comes out of the cylinder. Having scrubbers in place makes a measurable difference to air and water on the GC-MS.

Peter

IdiotFool,

I don't have any scrubbers in line but I do it to prove a point that my detectors work just fine without multiple purifiers in line. I use 5 nine's helium, nitrogen, and hydrogen and use welding grade argon for my applications.

Depending on your upper temperature range for your GC analysis, I would strongly recommend water and oxygen traps and I would make both of them indicating to tell you when to change them. For GC/MS analysis, I also recommend water and oxygen since you can significantly affect ionization when these are present. Unfortunately, that still leaves you on the lookout for nitrogen if you have issues. What I have found is that once in a while you get a bad cylinder. You may not notice it because your scrubber pulls out impurities or you may notice something like nitrogen when the scrubber is pulling out the oxygen from the air in your helium.

Best regards,

AICMM

Thank you both for your suggestions. Mine is a split FID and MS detector so purity is key. I suppose having a redundant filtration system is not a negative, just an up-front expense. I concur with the visible indicators so I change the filters out when necessary.

Thanks, again.

As a general rule I advise my UK customers to run without filters.
It is a benefit to have filters to extend column life, to get a better background etc.
However few customers take enough care. Most of the contamination comes at cylinder change time. If you don't look after your filters and change them when needed you will have far greater problems than running with none.
That said UK gas quality is good

As a general rule I advise my UK customers to run without filters.
It is a benefit to have filters to extend column life, to get a better background etc.
However few customers take enough care. Most of the contamination comes at cylinder change time. If you don't look after your filters and change them when needed you will have far greater problems than running with none.
That said UK gas quality is good

Thank you for the information. What specific recommendations do you have for changing out high purity cylinders, especially with a highly flammable gas like hydrogen?

My experience is similar to CE - folks never change the filters, so who knows when they are the source of the problem. Otherwise I would agree that filters should be used and changed routinely.

Re hydrogen, a bronze wrench is recommended to avoid sparks (this is often ignored as well).

Changing out cylinders - a toggle valve at the tank is helpful to reduce the amount of air that gets in to the system. It is best if the column ovens are reduced to ambient when the change is done, then give a few minutes before heating to purge any air out of the system.

The most elegant way of keeping air out of the system during cylinder changes is a switchover manifold, but you need to have two cylinders connected.

Peter

Agreed, Peter. We do that with one of our setups - just 2 tanks using shut off valves as the first step from the regulators. All manual switching, the autosystems for sale are freakishly expensive.

Agreed, Peter. We do that with one of our setups - just 2 tanks using shut off valves as the first step from the regulators. All manual switching, the autosystems for sale are freakishly expensive.

Rather than having the switchover valves downstream of two regulators I prefer having the switching on the high pressure side, with only one regulator, then the volume that you have to back-purge is smaller and there is almost no chance of filling the regulator up with air. Having said that, in my current lab I just have a single cylinder set-up on each gas.

Peter