nitrogen gas purity

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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What is the general requirement for LCMS nitrogen gas purity? is 95% above sufficient for lcms? Will O2 oxidize instrument?

See typical requirements for Agilent LCMS on page 18 in document below: ... 0Guide.pdf


Tomasz Kubowicz
let me add a couple of comments:

-MS vendors usually recommend very high N2 purity even though they know that no nitrogen generator can reach such values at working flow rates (500-1200 l/h). The higher the flow, the lower the purity.
-Certain instruments use zero (dry) air instead of N2 for nebulizing and drying gases in the source, e.g. the QTRAP from AB Sciex.

So in the end, purity should not really be a concern. Any nitrogen generator designed for LC-MS should do the job. The question is rather about the robustness, maintenance costs, quality of the service etc.
jiangds06 wrote:
Will O2 oxidize instrument?

Depends on the temperature of the internal components. If you have heated quads then it could be possible, but most are not heated above 100C. Most GC/MS instruments with heated sources allow venting once the source is below 100c which is where they consider it safe from oxidization.
The past is there to guide us into the future, not to dwell in.
Peak Scientific published an interesting little study on this, showing that some oxygen in the nitrogen had little to no effect on the ionization and detection of compounds. Since they provide high purity N2 systems I found it illuminating.

Gaetan correctly points out that no system provide >99.5% N2 at high flow rates. I have actually checked ours (Peak Scientific NM30LA) and at high flow rates it runs around 96-97% N2. I have a Waters Quattro Micro and we have tested it on compressed, dried air and it works about as well as N2. I like my N2 generator; it generates really nice, dry, clean N2, so I have stuck with it but I didn't see any appreciable difference between N2 and air.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
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