Optimizing thermal desorption paramters

[MMJ88]

Hi there,
I'm working a Gerstel TDSA2 connected to an Agilent 7890 with a microECD detector. I'm looking at Chloroform, 1,1,1-Trichloroethane, and Carbon Tetrachloride. We are collecting on Gerstel Carbotrap 300 tubes. I have been working on optimizing the method on the GC, to good effect. However, I know very little about the thermal desorption. I'm not sure the parameters are the best. I suspect I'm not getting the compounds on the column as quickly/cleanly as possible, and such the peaks may be wider. My current parameters are as follows:
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Initial:

Initial Temp: 50C (Actual 65C)*
Delay Time: 0.20 min
Initial Time: 1.00 min

Ramp:
60C/min to 275C, hold 5 min

Settings:
Transfer Temp: 275C (Actual 275C)
Vent Time: 1.00 min

Desorption Mode: Solvent Vent
Sample Mode: Sample Remove

I don't know what the gas flow is. The physical controller hooked up to the Gerstel stuff says "Adsorption flow: 21 ml/min", but the software says "Adsorption flow: 50 ml/min".

I'm splitting the flow at my inlet at about 20:1. We look at low levels of chloroform (which is not the best ECD-sensitive compound), so it necessitates the lower split ratio.
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*What does this mean? Why is the "Actual" temp different?


Does anyone have experience in this area? I would appreciate some pointers on what I should try. I don't particularly understand the relationship between all the parameters. I'm having a hard time finding anything online, and I don't have any useful material from the manufacturer.

Thanks.

[Alexandre]

TD analysis is complex. You have 2 instruments that have to be synchronized to work the way you need. Actually ECD is the best for CHCl3.

First – achieve good chromatography of manual 1 mL injection of air with CHCl3. You need static dilution bottle/s to prepare air standard/s.
Then when you fully satisfied with split, sensitivity and chromatography connect Gerstel. Check real flows with flow meter. Start with manufacturers recommended conditions. Spike tubes with std in MeOH that will give you comparable concentrations to 1-mL manual injections.
Good luck.

[remaou]

Hi MMJ,
What is the temperature of your injector during the desportion (cryocooling) ? If the pics of your compounds have not a nice shape, it may be because they are not focused in the inlet as well as they should (?).