Finally, some increased sample loading capacity for PAHs! Part 4: 30m x 0.32mm x 0.50µm Rxi-5ms

This may be the last post in my series on sample loading capacity for PAHs on Rxi-5ms GC columns.

Sample loading capacity for PAHs on a 30m x 0.25mm x 0.25µm Rxi-5ms GC column

Does a thicker film GC column increase sample loading capacity for PAHs? 30m x 0.25mm x 0.50µm Rxi-5ms

Sample loading capacity for PAHs, part 3: 30m x 0.32mm x 0.25µm Rxi-5ms

I finally got an obvious increase in sample loading capacity for PAHs by going to a 30m x 0.32mm x 0.50µm Rxi-5ms:  bigger bore x thicker film.  I say “obvious” because now I can see it by the peak shapes in the chromatograms (essentially answering Jaap’s question – “What do chromatograms tell us?”).  I think in the interest of not being long-winded, I’ll let the chromatograms tell the story and summarize the series below.  As previously, the EZGC™ Method Translator was used to provide the GC conditions when going from the 30m x 0.32mm x 0.25µm Rxi-5ms to the 30m x 0.32mm x 0.25µm Rxi-5ms.

  1. PAHs, especially larger ones like benzo[b]fluoranthene (5 rings) up to benzo[ghi]perylene (6 rings), and higher, easily overload 0.25mm x 0.25µm and even 0.25mm x 0.50µm 5% phenyl-type columns like the Rxi-5ms (and Rxi-5Sil MS) and corrupt overall peak capacity, separation efficiency, qualitative identification (particularly due to coelutions of isobaric species), and quantitative accuracy.
  2. If extra sample loading capacity (above ~10 ng each on column?) for PAHs is very important, a 30m x 0.32mm x 0.50µm column offers a balance between sample loading capacity and efficiency of separation, at the expense of increased run time versus 0.25mm columns.  (Note that the efficient flow rate for the 0.32 x 0.50µm column is going to be around 1.8 ml/min helium, so a mass spectrometer must be capable of pumping this flow.)
  3. Sample loading capacity estimates in ng on column may be lower than is typically stated and needs additional investigation with other compounds.

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