Can I use a non-MS column in my mass spectrometer?

Previously, I wrote about using a MS column for non-mass spec applications.  There are occasions when you come across a method or journal article where a non-MS column is used in a mass spectrometer.  People ponder if this is a good idea, and often contact Tech Support for guidance.  So, can I use a non-MS column in my mass spectrometer?

 

The simple answer to that question is you absolutely can.  There are times that based upon the target compounds, where the selectivity of one of these columns (ex: Rtx-1701, Rtx-20, etc.) may be required.  With that said, there are a few things to consider when installing these columns in a GC/MS.

 

With a capillary column in a GC/MS, you want to minimize any potential for column bleed.  Column bleed creates an elevated background, which decreases the signal to noise ratio.  If the signal to noise ratio is decreased, detection limits and quantitation limits become elevated.  Less bleed will also provide more reliable library matches and help minimize source maintenance.

 

To help minimize column bleed, start by using the thinnest film thickness that will provide the best separation for your assay.  The less film you have, the less bleed you may have.  Since you are using a MS, some coelution may be acceptable if quantitation ions are not common to both compounds.  A film thickness under 0.50 µm is ideal, but sometimes a thicker film is the solution.  Keep the transfer line temperature at least 20°C below the maximum temperature of the column.  Exposing the column to constant high temperatures in the transfer line will cause bleed.  Use the lowest possible oven temperature to elute/separate your compounds.  Again, try to avoid the column’s maximum temperature.  As a final note on bleed, remember that the potential for column bleed increases as polarity increases.  A polyethylene glycol (wax) column will exhibit higher bleed than its less polar (dimethyl polysiloxane) cousin, such as the Rtx-1.  But, always use the best column for your separation.  It’s all about the chromatography, so you may need to clean your source a little more frequently.

 

With a PLOT column, one needs to keep any particles generated out of the source and the instrument’s turbo pump (if equipped).  The best way to do that is with at least 5 meters of 0.18 mm or 0.25 mm internal diameter fused silica column.  This section of capillary column can act as a particle trap and can handle the pressure drop of the MS vacuum.  My colleague Jaap de Zeeuw wrote a blog post containing this information. I do want to emphasize that a good connection must be made.  This can be problematic for leaks.  Ideally, detectors, such as thermal conductivity (TCD), flame ionization (FID), or discharge ionization (DID) are better suited with PLOT columns due to the nature of the compounds being analyzed.

 

So, if you are contemplating a non-MS column for your GC/MS, review the considerations above and go for it.  By following the above guidelines and knowing what you are getting into, you will be able to obtain reliable chromatography on your GC/MS.  The tradeoffs can often times be worth the selectivity derived for one of these columns.  Thank you for reading and good luck with your analyses!

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