Chromatography Forum

I have a 5890 that is plumbed in a way that helium gas is the make up gas. So on the auxilliary panel, I have the 3 pressure regulators for Helium , Air and Hydrogen. Helium is split for use as carrier gas and also as makeup gas.

To use Nitrogen as make up gas would I need another external regulator? Any ideas on how to proceed with this replumbing?

Also is it possible to transplant a cool on column injector from a 5890 with NPD onto a GC with a split/splitless with FID ? (5890 series II both)

I don't think it can be done easily as the make up gas comes from the fid gas box. You may be able to rig something up but you would have to some how connect the make up tube to the FID to a stand alone mass flow controller.
I always used He as the FID make up gas.

You should be able to swap inlets on a 5890.

Yes, you can run just nitrogen as the makeup. You would use the cylinder regulator to control pressure but make-up is also controlled by needle valve on front of 5890. Separate line from cylinder to make-up gas port.

Probably easier to swap the FID with the NPD than it is to swap the injectors.....

Best regards,

AICMM

I don't think it can be done easily as the make up gas comes from the fid gas box. You may be able to rig something up but you would have to some how connect the make up tube to the FID to a stand alone mass flow controller.
I always used He as the FID make up gas.

You should be able to swap inlets on a 5890.

May I ask why you have used He as a make up gas? I've noticed many labs do that. But how do they justify the extra gas cost ? And the loss of sensitivity? How less sensitive is the FID this way to begin with?

In my experience it is the default in most labs to use Helium as the makeup. I suspect that it's just less work to run three instead of four gas lines. Further, many instruments were plumbed this way. We just bought two 7890's last year. To convert them to nitrogen, we had to get into the bak panel and redo some lines. Not a ton of work, but the GC certainly wasn't built to make it as easy as it could be. More work than changing the 6890, which has a separate gas connection for makeup.

I've always used nitrogen make-up on helium or hydrogen carrier gas. Shoudl be easier to change on a newer instrument, just replumb and set your method I think.

Will use of nitrogen as a carrier gas, in place of helium affect retention times, peak shapes, or response factors?

Will use of nitrogen as a carrier gas, in place of helium affect retention times, peak shapes, or response factors?

I'm going to answer my own question here. I found a good reference on-line: http://www.gasesmag.com/articles.php?pid=70

I notice some significant retention time differences from an ASTM method (it specifies He, contant flow, I'm using N2, constant flow, as carrier). I'll need to adjust my flow rate.

Nitrogen isn't as "good" a carrier as he/H2 but if you have lots more resolution than you need then you don't need the best carrier, it's money for nothing.

Yep my instruments were set up that way too. I have a 5890 IIa with an FID and a 6890 with an FPD. It was before my time from an era when He was cheaper.

I am probably going to replumb it to use N2 as well. I have an N2 cylander and regulator nearby but it is only used for blowing down samples currently. I am in the process of setting up the 5890 to run amino acids using alkylchloroformate devivitization.

My 5890 has small black regulators inside the instrument side compartment but no guages. There is a separate line and input for FID makup and injector inlet. I use a flowmeter with adapter on the FID chimney to set flows. It should be just some replumbing and do I need a gas purifier for the N2?.

Nitrogen isn't as "good" a carrier as he/H2 but if you have lots more resolution than you need then you don't need the best carrier, it's money for nothing.

I have to disagree slightly - the maximum resolution that you can get with nitrogen is as good as with helium or hydrogen, but becuase you need a slower linear flow rate to get that resolution with nitrogen the separation takes longer (nearly four times as long with nitrogen as with hydrogen). Also there is a broader "sweet spot" on the van Deemter curves for the two Hs, which allows columns to be run with fater than "optimum" flows to get separations done even quicker.

So nitrogen is just as good a carrier, but it does its job a lot slower.

Peter

I stand corrected, have just looked up the curves and Peter is of course right. Don't tell anyone, our helium profits will slump...

do I need a gas purifier for the N2?

An emphatic yes! You should always use purifiers for all of the gases for your instrument.

I stand corrected, have just looked up the curves and Peter is of course right. Don't tell anyone, our helium profits will slump...

Not as long as time is money they won't !

Peter

So , can someone comment on the benefits of using He vs N2 as carrier gas nowdays with today's prices, and in regards to sensitivity and noise?