Hydrogen as Carrier gas without using Quench gas QQQ

Hi,

a technician told me that I should turn the quenchgas off by using hydrogen as carrier gas.

I compeared the measurements and found out: He is right. S/N is better and there are more peaks.

I wondered why? By using Helium as carrier gas you should always use Helium as quench gas, too. Otherwise you`ll get not the best S/N:

https://www.agilent.com/cs/library/slidepresentation/Public/7000BeSeminar_Dec09.pdf

does somebody knows why?

An other question:

Why should you use a 6mm instead of 3mm extractor lens for using hydrogen as carrier gas?

Thank you

  • The helium quench gas in the collision cell is there to reduce the transmission of helium metastables formed in the ion source from progressing down to the detector and showing up as background signal. There are no metastables formed with hydrogen so no need for it to be used as quench gas.  

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    GCMS systems will always work better with helium due to chemistry and physics. The use of hydrogen requires changing some things in Agilent GCMS systems and the way systems are used.  The physics inside of a GCMS ion source are much more complicated than in any of the typical GC detectors.  The small size and high speed of hydrogen molecules inside the ionization chamber and analyzer manifold under vacuum operate very differently than when using helium. The pumping capacity is ~60% of that running hydrogen.  Hydrogen is very chemically active and that activity will affect some compounds differently than others.  While most spectra remain the same, there are always exceptions. Users should check the reference spectra for important targets to make sure they have not changed.  It is also necessary to verify target/qualifier ratios.  Some compounds may even disappear at low levels. It can cause chemical activation of surfaces inside of the MS, even of inert metal surfaces.  It is not a 1:1 direct swap -- the system WILL perform differently running hydrogen carrier gas.

    • Pumping speed for H2 is ~60% of He, so the allowable maximum flows into the MS are much lower. Be careful during pulsed splitless as the pulse pressure may possibly cause too much flow into the MS.

    • Inlet pressure should always be >= 5psi, no matter the carrier gas. That’s a serious limitation if the operator tries to run the same column and flows using H2 as they do with He.   
      • One good way to achieve this is to use a 20m x 180uM column.
        • Helium:            30m x 250um x .25 column at 35°C oven and 1.2ml/min = 8.83 psi
        • Hydrogen:       30m x 250um x .25 column at 35°C oven and 1.2ml/min = 1.15 psi
        • Hydrogen:       20m x 180um x .25 column at 35°C oven and 0.75ml/min = 5.06 psi ….just above the minimum recommended inlet pressure.
      • The column flow should be reduced to between 0.4 and 0.75 ml/min to try to minimize the spectral tilt differences in scan.  Ionized H2 does CI so there may be some CI like appearance to spectra – more molecular ion.
      • Use pulsed injection, especially with small bore columns, to get the sample onto the column in a narrow band at the lower necessary column flows. 
      • Use the lowest inlet temp that works to reduce reactions with H2.  Consider using an MMI or PTV in cold splitless mode for fragile compounds.
      • Avoid using methylene chloride, in fact most chlorinated solvents, especially wet. – At higher inlet temps, like >280C, with H2 carrier gas - HCl is formed.  If it must be used, use the lowest inlet temp and maybe the optionally available deactivated S/SL or Multimode inlet weldment.
      • Use liners with a taper at bottom (like the Agilent Ultra Inert Splitless Single Taper or Splitless Double Taper)
      • H2 is not an inert gas, so check for inertness problems with your analytes.

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    Reducing the column flow and using the draw out/extractor lens with the larger hole helps to minimize the issues with hydrogen by letting it escape from the ionization chamber faster.  The 9-mm Draw out or Extractor is recommended for most applications with hydrogen carrier gas, as it provides the best overall performance, balancing sensitivity, peak shape, and source reactivity. The 6-mm lens can be used if greater sensitivity is required but it is best to start with the 9-mm first.

    ■ Inert  draw out 9mm: G3440-20022    ■ Inert draw out 6mm: G2589-20045    

    ■ Extractor 9mm: G3870-20449   ■  Extractor 6mm: G3870-20448

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  • a fun fact. Some hydrogen molecules are going faster than earth's escape velocity.  They can be going as fast as 16.2km/s and the escape velocity is 11.2km/s.

  • Wow!! Thank you very much for the very good and helpful answer

  • In the 7000D/7010B Operations manual Page 115:

    If you search that pdf manual, hydrogen is mentioned 124 times so some of the details might be overlooked. Using hydrogen has generated a lot of questions lately. 

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