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Can I analyze NO, N2O and NO2 via GC?

29 Feb 2012

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This question pops up a number of times every year.  The joking answer my former colleague Dick Zwiep (when we both worked at Chrompack time) used to make was:  No and No-two!

The challenge is not the N2O, but the NO and NO2NO and NO2 are involved in several reactions/equilibria, that makes the quantification challenging.

N2O  (Nitrous Oxide) , also known as “laughing gas”, is quite easy to analyze via GC. One can do that on a porous polymer type phase, like the Rt Q-BOND, see fig.1.  The N2O elutes quite fast, meaning that a splitted injection is preferred. In this application a 0.25mm PLOT column was used as the detector was an MS. N2O is also often measured via ECD.

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Fig.1 Nitrous oxide elutes as a symmetrical peak from a Rt-Q-BOND porous polymer.

NO,  (Nitric Oxide), is more challenging to measure.  When exposed to oxygen, NO is converted into NO2 (Nitrogen Dioxide), which has a dark brown color.

2 NO + O2 → 2 NO2

This is also one of the challenges that is faced. NO will immediate react with O2. If O2 is absent, NO will elute from most columns, but it will show minimal retention. Even on a porous polymer it co-elutes with permanent gases.

It is retained on Molecular sieve type adsorbents and  can be measured, but peak shapes are usually not symmetrical, which challenges elution and detection  of low levels.

Some more models of chemical kinetics on NO/NO2 can be found here: http://www.chem.tamu.edu/rgroup/hughbanks/courses/102H/lecturenotes/class12-1.pdf

NO2, (Nitric dioxide), is most challenging to analyze via GC.   NO2 exists in equilibrium with dinitrogen tetroxide (N2O4):

2 NO2 <=>     N2O4

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Fig.2 Reactivity of porous polymers based on vinylbenzene, with NO2 makes quantitation difficult

Few applications are out there. Most obvious would be to use porous polymers for this, but the Nitric dioxide reacts with the porous polymer forming an ethylene peak, see fig.2,. This maybe a way to measure NO2 indirectly by converting the NO2 into ethylene in a hot inlet, however, the conversion is believed not to be quantitative.

For low level detection one can use MS, ECD, PDD ands also Cheluminescence detection. TCD is also possible, but only at high ppm levels

Author

  • Jaap de Zeeuw

    Jaap is a world-renowned chromatographer with over 40 years of experience, including 15 years with Restek and 27 years with Varian/Chrompack prior to joining Restek. Throughout his career, Jaap has focused the chromatographic challenges of industrial analysis. For his 1979 graduation from The Institute for Higher Education, where he specialized in chemistry, Jaap authored a paper titled "The Challenge of Coating Flexible Fused Silica Capillary Columns" and has since distinguished himself as an authority on the subject. Jaap has been directly involved with the creation of numerous chemically bonded columns, including the first bonded PEG column and the stabilized PLOT columns widely used in the petrochemical arena. He has also helped develop new techniques, such as fast GC-MS using vacuum GC technology (low-pressure GC or LPGC). Over his innovative career, he has filed several patents for his work. Based out of the Netherlands, Jaap is extensively published and regularly travels internationally to share his knowledge. After retiring from Restek, Jaap founded CreaVisions, where he works as a GC Consultant and teaches master classes on key GC topics as well as on creativity in science.

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