I have a GC with a peak pair I'm interested in separating but are not getting resolved cleanly at the moment. Any tips on what temperature programming tweaks might help me?

The problem pair elutes at about 3.3 mins. The temp program was 120 C for 2 min followed by a 8 C/min ramp to 180 C & a final hold of 5 min.

Changing the column, detector or carrier gas is not an option. I want to just get the best I can by temp. programming optimization.

I've tried isothermal runs at 120 & 100 C but not much help. The peaks still come unseparated.

Since it is just this two peaks that interest me mostly, theoretically a ramp is superfluous isn't it? Just figuring out the right isothermal run ought to give me the separation of interest?


The column is an OV-351 packed col. 2 m long and 1/8" in diameter. N2 carrier gas with FID. The molecules are:

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  • 2
    $\begingroup$ Can you give any more details about the column/setup you're using, and the molecules you're trying to separate? $\endgroup$
    – NotEvans.
    Commented Oct 9, 2016 at 15:11
  • 1
    $\begingroup$ Try diluting your compounds. $\endgroup$ Commented Oct 10, 2016 at 3:48
  • $\begingroup$ You could also try derivatisation $\endgroup$ Commented Oct 10, 2016 at 3:49
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    $\begingroup$ If time is not an issue. Go for an isotherm at low temperature. $\endgroup$ Commented Oct 10, 2016 at 3:58
  • $\begingroup$ @QuantumCAPUCCINO Yep, time's not an issue. I'll try isothermals at 70 / 80 / 90 / 100 C. What Temp. would you try? Any others? Even lower? $\endgroup$ Commented Oct 10, 2016 at 8:37

1 Answer 1


I just thought that the rearrangement might be occurring during the analysis I.e. The thermal ramp, implying a lower temperature would be better for you. The bp of each compound is too close to separate purely in that way.


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