Using the Restek EZGC Method Translator to Assist in GC Column Trimming Maintenance

It is well known by people who analyze environmental and food safety matrices for semivolatile organic compounds like pesticides and PAHs that you occasionally have to trim the GC column to restore peak shapes degraded by nonvolatile matrix material that builds up on the inlet side of the column. What gets a bit murky is how you change the GC conditions after trimming to maintain the same elution orders for peaks of interest.  Consider using our new EZGC^TM Method Translator and Flow Calculator (MTFC).

In the example below, I’ve made three (exaggerated) trims on a GC column that had an original nominal length of 30m, our 30m x 0.25mm x 0.25µm Rxi-5ms, which resulted in a column length of 23.7m.  Using the MTFC, enter the Original column dimensions, and the original GC conditions.  Keeping the flow rate the same, enter the Translation column length, and simply watch MTFC spit out the updated oven program rate for you, which it will do when you have “Translate” selected under Results.  Note that the 30.7m and 23.7m chromatograms look almost identical, except that the 23.7m run is faster due to the increased oven program rate necessary to keep compounds eluting at the same temperature (the thing they need to do to avoid elution order flip-flops).

That faster run creates a bit of a problem, the need to update any Selected Ion Monitoring / Selected Reaction Monitoring windows and/or Calibration Table Expected Retention Times.  Again, MTFC to the rescue!  Just use the “Speed” factor in Results to calculate the expected retention times, as follows:

Predicted retention times for Translation = Actual Original retention times divided by “Speed”.

The table below indicates the calculation above works very well.  Now, just cut and paste the new retention times into the method and calibration areas and keep using that same column and save money.

If you want to follow along with this example, the Original Method and the Translation Method are:

--------------------------------------------------------------------------------------------------------------------------

30.7m x 0.25mm x 0.25µm Rxi-5ms, 1.4 mL/min constant flow He, GC-MS, split injection

Oven:  90°C (0.1 min), 8.5°C/min to 330°C

--------------------------------------------------------------------------------------------------------------------------

23.7m x 0.25mm x 0.25µm Rxi-5ms, 1.4 mL/min constant flow He, GC-MS, split injection

Oven:  90°C (0.1 min), 12.5°C/min to 330°C

-------------------------------------------------------------------------------------------------------------------------