HS-GC-FID: Issues with Ethanol

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

3 posts Page 1 of 1
I'm trying to develop a method for ethanol via headspace. I am using Restek standard Residual Solvents #1 (34105) for the curve. My instrument is Agilent 6890 GC-FID with CTC PAL COMBI autosampler for headspace.

I ran residual solvent curve at high concentration (1500ug to 150ug off instrument), there was no linearity. I then ran a curve using liquid injection, the curve was almost perfect. So there's something going on with my headspace. From looking at the curve, it looks like there's some kind of saturation at higher concentrations.

I then ran a 3-point curve with lower concentrations (240 to 60). Way better linearity, but still not great. I’m also noticing that at higher concentrations, the ethanol peak is way smaller than it’s surrounding compounds. At lower concentrations, the ethanol peak is higher in comparison to the surrounding compounds.

I don’t believe this is detector saturation, but something else is going on because: The peak shape is showing no signs of saturation (peak fronting or flat tops). Also, running at a higher split ratio does not seem to help. So my question is, why is this happening?

Here are my current run conditions:



Inlet:

Temp: 150

Split: 50:1
4mm Straight Topaz Liner

Column:

Constant flow at 2.0 ml/min

Hydrogen gas

Oven:

33, hold for 6

15 80 0

55 250 1



Detector: 320



Headspace (CTC PAL):

Injection Volume: 500uL
Incubation temp: 80

Incubation Time: 1800

Syringe Temp: 110

Injection Speed: 500

I couldn't attach my pictures, but I also posted this on the Agilent forum with pics
https://community.agilent.com/technical ... -happening
What are you diluting the Restek standards in? I see it is shipped in DMA - are you using DMA to make dilutions also?
What is the ethanol dissolved in ?, and what samples do you intend to use the method on?
Peter Apps
3 posts Page 1 of 1

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