Adapting Method from Helium to Nitrogen

[Kenneth J. Welch]

Capillary GC methods are developed in the US and then used by laboratories in US and elsewhere. The US labs use helium so the methods typically specify helium. The non-US labs often don't have access to helium and hydrogen may be discouraged by policy. Nitrogen seems to be in regular use for capillary GC for the non-US cooperating laboratories. Most labs use the same pressure and linear velocity as specified for helium. The u-opt value for helium considerably above the u-opt for nitrogen. In our case, esolution is not usually an important criterion. However, does anyone have a "rule of thumb" for the % reduction in resolution or % change in number of theoretical plates?

[chromatographer1]

I would think that any estimation would be exactly that, an estimation. And what counts is certainly 'what is'. Whether it is one half or one third, does it really matter? The capacity of nitrogen to hold an analyte in the gaseous state versus helium is an important factor in your analyses, of course. And if this degradation of performance is really so important, then the management should use hydrogen. Really, the 'old wives tales' about hydrogen use is really not applicable in today's instruments. Twice the performance as helium and a lot cheaper too. Any well ventilated lab should have no concerns using hydrogen, especially if the cylinders can be kept outside and the gas piped into the lab.

Someone should have a serious chat and educate your administration.

OK, I am off my soap box now for the rest of the day.

best wishes,

Rod

[Peter Apps]

This is a hardy perrenial - run a search on the forum archives and you will find reams of "discussion". In crude outline; the maximum resolution that you can get out of a system (presuming that it is the usual 20 - 50 m 0.25 - 530 mm i.d. column etc) is closely similar for all the carrier gasses. What differs is the time that it takes to get the separation done, which is in inverse proportion to the gas flow rate. In other words you can run 4 times as fast with hydrogen as you can with nitrogen, or put another way one GC can do the work of four.

Using hydrogen as carrier gas is no more dangerous than using it as FID or NPD fuel. Of course you cannot use it in an MS, but then nitrogen would probably give you pumping and source pressure problems as well.

Peter

[MikeD]

As a matter of interest, what countries are we talking about that don't have access to purified helium?

[kamlesh.vaishanav]

Hey, I m telling about the physical nature of nitrogen is different in many ways to the Helium, e.g. 1. In density 2. In inertness.

These things also effects on carrier gas and analyt intractions, retention time of the analyte and even peak shape, limit of detection and area of the peak. so all parameters should be taken in considerations then finalize the gas.