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Ethylene glycol RT shift issue

Question asked by wendywen on Jun 8, 2017
Latest reply on Sep 19, 2017 by wendywen

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

 

NOTE:

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.

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