Carryover Peaks - problem Please help

Discussions about GC and other "gas phase" separation techniques.

3 posts Page 1 of 1
Hi guys!


I am currently trying to do a calibration of my compounds in HS GC. The problem which I am having is that I always have some carry over peaks appearing from the previous samples.

Now, the problem is that if I would like to do a calibration for quantitative measurement of let's say, one compound in the ranges of 50 000 ppm to 100 ppm, and would like to run the different concentrations one after another, because of the carry over, I would potentiality have bad calibration because the carry over peak will add on the peak which is really measuring.

What I have found in the literature, is that to prevent contamination and remove the residual compound vapor from the previous headspace extraction process in the first headspace GC analysis, fresh helium purging must be performed after each analysis.

Now the question finally, how to do this purging?


Just to say, I am completely new to this analytical technique so I would not know how to even do this in the HS GC that I am using. Please help.

I already have the method developed:

Gas chromatograph conditions (HP 6890)
Column: Capillary column SGE BP20 (Polar phase)
Length: 25m
Thickness: 1m
Internal diameter: 0.53mm
External diameter: 0.68mm
Detector: FID FID Temperature: 250ºC
Injection: Automatic
Software: ChemStation.
Carrier gas: Helium
Injector temperature: 200ºC
Inlet pressure: 4.31 Column flow: 7mL/min (constant).

Temperature profile: 35ºC (during 6 min); ramp until 80ºC at 10ºC/min (kept constant during 2 min); ramp to 120ºC at 40ºC/min (constant for 2 min).

HP 7694 E auto sampler

Vial temperature: 130ºC
Sample loop temperature: 170ºC
Transfer line temperature: 180ºC
GC cycle time: 28 min
Vial equilibration time: 15 min
Pressurization time: 0.13 min (17.8 psi)
Sample loop filling time: 0.02 min
Loop equilibration time: 0.05 min
Injection time: 1min
What is your column max? Could something be left on the column from previous injection? Ramping higher or longer to see if anything comes off. 120 seems low. I would think youd want this over your vial temp of 130, at least.

You could have contamination in the headspace flow path, or GC inlet.

Headspace flow path should always be purging with He by default. GC depends on your inlet type. Is it EPC S/SL or PCM? S/SL will have different options for purging times.
Thanks a lot for your interest in my topic.

The problem was the accumulation of the residual compounds in the cold spots at the inlet together with dirty vials from the supplier. With new liner, septum, cleaning and new box of vials the problem disappeared!
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