Ethylene glycol RT shift issue

I am using GC6890 /MS5973 and COmbi PAL headspace to analyze ETHYLENE GLYCOL and other solvents. But always got RT shifts with concentration increase.

anybody could shine any lights for me to find the bug?


Here is detail infor:


Ethylene Glycol Peak RT shift issue


concentration of ethylene glycol = 2.5 ug/ul, pipette the following amount to 10 mL headspace vial for each calibrator


Calibrator 1, Ethylene Glycol Peak RT = 8.35 min, Amount = 0.8 uL

   Calibrator 2, Ethylene Glycol Peak RT = 8.38 min, Amount = 1.5 uL

   Calibrator 3, Ethylene Glycol Peak RT = 8.47 min, Amount = 2.5 uL

Calibrator 4, Ethylene Glycol Peak RT = 8.92 min, Amount = 5 uL

    Calibrator 5, Ethylene Glycol Peak RT = 9.22 min, Amount = 10 uL



1)other solvents RT are always consistent without any shifts

2)The calibrators were prepared by spiking pure analytes into triacetin.

3) 250 uL headspace gas was injected by CTC Combi PAL.

4) The peak width becomes wider with increasing concentration, peaks is showing tailing for calibrator 4 and 5

5) Peak area is linear for first three calibrators, then suddenly drop for calibrator 4, then back for calibrator 5.

6) RT for same calibrator (repeated injection) are consistent without any shift

7) All above obServed information could be duplicated by running another batch of 5 calibrators. We repeated several times, always got same results like above.

8) Inlet liner is Agilent ultra inert PN 5190-2293

9) GC conditions: Inlet 250 C, split 10:1, flow 4.0 ml/min, oven 35C hold 1.5 min then to 300 C at 30C/min

MS interface 280 C, Scan 15-125 amu.

  • Hi Wendy,


    I assume you use a wax-column for the EG?

    With increasing sample load you get, as you mention, wider peaks, and also more asymmetrical peaks.

    The RT is determined as the apex of the chromatographic peak, at that determination will shift with increased asymmetri. It is a well known "feature".

    Possible solutions could be to reduce the sample load or to increase column capacity so that the peaks don't overload. This will help the peaks stay symmetrical with more constant retention times.


    If identification/localization of the peak with the quantitation software is the problem, try to increase the expected retention time window - that is if your separation allows unequivocal identification within a wider RT-window of course.


    Hope this helps.


    Best regards,


  • Karina


    Really appreciated your kind reply!


    But it is not overloading issue as we generally experienced. 




    Sent from my iPhone

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