Half the GC Column, Three Times Faster Analysis, Same Chromatogram!

Good things that happen when you go from a 30m x 0.25mm x 0.25µm GC column to a 15m x 0.25mm x 0.25µm GC column: 

  • You do NOT lose resolution by a factor of 2 by with the 15m column.
  • The sample loading capacity is about the same for the 15m column.
  • With GC-MS, you gain speed of analysis by a factor of about 3 with the 15m column.
  • With proper Method Translation, you get the same chromatogram with the 15m column.
  • The peaks are narrower and taller and better detected with the 15m column.
  • The cost of a 15m column is about half the cost of a 30m column.

See the chromatograms below.  Enough said…

Additional reading: 

Half the Column, Same Chromatogram. Trimming your GC Column and Maintaining Resolution.

Half the Column, Same Chromatogram: Maintain Resolution of BDE 49 and BDE 71 With Proper Method Translation After Trimming an Rtx®-1614 Column for Maintenance

30m to 15m Pest

4 Responses to “Half the GC Column, Three Times Faster Analysis, Same Chromatogram!”

  1. Dear Jack –

    Nice work. However, the peaks looks broader to me on the 15 meter column … Could you please add the y-axis on the chromatograms next time? …:-) And what about “unknowns” among the “knowns” in sample matrices. Does the 15 meter column work with real samples as well …?

    With kind regards –
    Lars Kurstein, Copenhagen

  2. Jack Cochran says:

    Hi Lars:

    It’s just an optical illusion of scale on the peaks looking broader on the 15m column. That’s why I put the FWHH information on both chromatograms. The peaks are twice as wide on the 30m column.

    The 15m columns are perfectly suited to “real world” targeted and non-targeted analyses. It’s not truly the “same chromatogram” as the 30m column, a bit of artistic license on my part there in the title, as the 30m does have more plates, so you might take a hit on spectral deconvolution when peaks get closer together on the 15m if you don’t have good acquisition speed. That said, if you do have the acquisition speed, like with TOFMS, you can define those narrow peaks properly and you only need about 4 spectra between peak apexes to get good spectral deconvolution, unless the peaks are isobars or have shared masses with a huge concentration differential.

    To sum up, it works, and we use the 15m x 0.25mm x 0.25micron columns often in our GC-TOFMS to quickly evaluate “real world” samples where we are checking a new cleanup procedure, a new cleanup sorbent, cartridge SPE breakthrough or loading experiments, whatever. It allows us to get 3x as many samples done in a day, very important for us.

    Thanks for reading and commenting,

    JC

  3. j de zeeuw says:

    One thing that we always need to consider, is that IF we start with a lower-resolution system, the Impact of ageing, contamination and activation will impact separations also faster. The world out there does not run only standards.
    That means that less samples can be run between maintenance intervals.

    The other challenge is: If 3x faster is implemented you have the speed advantage, but as column life time is determined by the nr of injections, it means that running 3x more samples in the same period, one need also to purchase at least 3x more columns.

    Add to this the impact of the ageing, I would not be surprised that you will use 4-5 times more columns in the same time period. One should be aware of that. But you always will have the speed advantage which should compensate for the extra column-costs.

  4. Jack Cochran says:

    Excellent comment, Jaap, and you fell into my trap, because this is a column that I trimmed down from 30.7m to 15.7m during a simulated “maintenance” experiment just to prove how long a column can work. Most customers throw away their columns way too early. I guess it’s in my nature to keep using things, as I am still driving my 2003 SUV!

    If you want to start with a short 15m column as in this example, presumably you are not just on the edge for critical separations, and you’re already using MS to get the 3x speed advantage versus a 30m setup, which provides “separation”, so then you’re looking for the throughput advantage, maybe to match up with a fast sample prep method.

    We don’t run only standards on this setup either. We very often use it for QuEChERS work, since QuEChERS is a fast sample preparation method. For quick evaluations of different modified methods, including cleanups, etc., as we are doing methods development, it’s unbeatable.

    JC

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