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Nitrogen Carrier Gas for GC – Is it Feasible? – Is it Practical?

30 Apr 2012

Jaap de Zeeuw and I discussed nitrogen carrier gas for GC today, its potential benefits, its drawbacks, and how it might be used “successfully” in more laboratories given the finite supply of helium and helium’s higher costs than nitrogen or hydrogen.  As sometimes happens, we don’t always agree on the finer points, so maybe we can get our blog readers to comment, too.    

I start with a slide I have for my GC training course that indicates some general points about helium, hydrogen, and nitrogen carrier gases, followed by a dimensionless van Deemter plot that demonstrates the performance of those carrier gases in a graphical way.  We want minimum H for the highest efficiency (the best chromatographic separation), which makes nitrogen the most efficient gas, but we also want the highest average linear velocity for the carrier gas while not sacrificing efficiency, which gives the edge to hydrogen.  The other thing we’d like, but has become less critical given that we can operate in constant flow or constant linear velocity mode these days due to electronic flow control, is a relatively flat van Deemter curve.  This allows us to stray outside of the optimum linear velocity and not lose too much of the separation, important, especially if we’re going with a higher linear velocity for faster analyses.  Hydrogen has the edge in this criterion.

Next, I show three organochlorine pesticides separations for helium, hydrogen, and nitrogen on a 20m x 0.18mm x 0.18µm Rtx-CLPesticides column where the carrier gas linear velocities and oven programming rates are close to optimum for maximizing peak capacity.  The peaks from left to right are: heptachlor epoxide, trans-chlordane, endosulfan I, DDE (4,4’), dieldrin, endrin, DDD (4,4’), endosulfan II, DDT (4,4’), endrin aldehyde.  Generally speaking, our expectations are met where we see a faster analysis for hydrogen versus helium, and a much slower analysis for nitrogen.  However, we do get a better separation for endosulfan I and DDE when using nitrogen.  Surprised?

Finally, I had blogged on this subject a few years back (title is below) and showed that even with nitrogen carrier gas you don’t always have to settle for slow analyses, as long as you have a highly selective GC column like the Rtx-CLPesticides.

"Donald Duck voices silent and birthday balloons fall everywhere as helium disappears..."

carrier gases

velocity curve