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Planning to use a PLOT column with a mass spec? You may wish to review this first.

10 June 2022
By
  • Alan Sensue
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Please note that (generally speaking) Restek does not recommend using any particle-containing GC column when using a mass spectrometer as the detector.  Particles will likely make their way into the detector/pumps even with a particle trap installed.  However, if you do plan to use a PLOT column with a mass spec, you should consider the suggestions below to minimize the number of particles which may make their way into your detector.

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Suggestions

  1. Use a different detector if you can. I suggest reviewing this blog post if you plan to analyze gases (or small compounds) with a mass spec.  When NOT to use (GC) Mass Spec (restek.com)
  2. If a mass spec must be used, use a 0.25mmID PLOT column. These smaller internal diameter columns are preferred, not only because they limit the carrier gas flow into the detector, but also because they contain fewer particles which will lead to less mass spec contamination (and less frequent source cleanings).
  3. Instead of using a particle trap kit (which is fine for non-mass spec detectors), connect a 15-meter Rxi-1ms column like Restek # 13335 to the outlet of the PLOT column to minimize the pressure fluctuations which can cause particles to dislodge from the PLOT column when the vacuum pumps are turned on or off.
    Rxi-1ms Columns (fused silica) (restek.com)
  4. Only use a glass connector to connect the PLOT column to the particle trap column.  A glass connector like 22159 seems to work well for our customers.  Never use a connector which uses (compression) ferrules.
    Defined PressFit Connectors (restek.com)
  5. Only use 100% graphite ferrules at the injection port.

Additional notes

  1. Porous polymer PLOT columns will produce very high bleed levels at higher temperatures compared to mass spec grade columns like a Rxi-5ms. Therefore, it is highly recommended not to exceed 150°C for the Q-Bond, and 125°C for all other porous polymer PLOT columns (QS, S and U-Bond).  The suggested temperature limit for Alumina PLOT columns is 200°C (except for the Rt-Alumina Bond/MAPD, which is 250°C) and for the Molecular Sieve 5A, is 300°  These temperature limit recommendations are the maximum temperatures for the injection port, GC oven, and mass spec transfer line when using these columns with a mass spec.  Temperature limits are higher with other detectors when column bleed is not as much of an issue.
  2. Never perform on-column injections using a PLOT column as the syringe needle will dislodge particles.
  3. Keep moisture and carbon dioxide from entering Alumina and Molecular Sieve 5A PLOT columns as these compounds will degrade the column’s performance. Refer to the PLOT Column Instruction Sheet for column drying/regeneration tips.

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