Baseline rise when switching from helium to nitrogen carrier

[pacerlaser]

Hello, I am currently trying to switch our 5890 GCs from using helium as a carrier gas for a FID to nitrogen. Everything has been good but I have noticed that there is a greater baseline rise when using nitrogen. I've tried lowering the carrier gas flow rate using a flow meter but no luck. Is it just the nature of nitrogen to cause a baseline rise? The columns I'm using are fairly new so I don't think its column bleed and the only thing I have changed is the gas from helium to nitrogen. Does anybody have any recommendations? Thanks in advance!

[thohry]

I think it's due to the quality of the carrier gas. Helium is often very high quality.

[AICMM]

Pacerlaser,

Can I propose you consider carrier switching? Depending upon the application, it is entirely possible to stay with helium during the analysis and switch to hydrogen or nitrogen for the idle times. It's very easy to implement as well.

I have posted my Pittcon poster on the topic on my web site. Click on the HERE button under What's New:

www.gcsrus.com/applications.htm

There are some applications that don't fit the bill but after you have had a peek you can contact me if you want further information.

Best regards,

AICMM

[pacerlaser]

I'm thinking the real problem lies in the fact that I don't have an EPC with the 5890 GCs. I am setting the flow rate when the GC is at its starting temperature but the baseline rises near the end of the analytical run. I'll try setting the flow rate when the GC is hot and see if that makes a difference. Thanks for the suggestions!

[James_Ball]

http://www.slideshare.net/jvercamm/the- ... 49#btnLast

There are some interesting ideas about using Nitrogen as carrier in that document.

Also, I believe that nitrogen makes FIDs more sensitive so when using nitrogen instead of helium you may be seeing more column bleed simply because the detector sensitivity is much higher.

[MichaelScottCalhoun]

I'm thinking the real problem lies in the fact that I don't have an EPC with the 5890 GCs. I am setting the flow rate when the GC is at its starting temperature but the baseline rises near the end of the analytical run. I'll try setting the flow rate when the GC is hot and see if that makes a difference. Thanks for the suggestions!

Where are you making your adjustments from ? Head pressure from source carrier or pcol needle valve ?

[Peter Apps]

If you have oxygen and moisture filters on your carrier gas supply then there is nothing about nitrogen that will cause an extra rise in baseline. Keep in mind though that even if both are the same purity in the cylinder the nature of the impurities is probably different, which might have an impact.

What are you using as make-up gas, and have you changed that as well ?.

Has the signal per unit mass of analyte increased since you changed carrier ?

Peter