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TTHM analysis on ECD- new to this method
Posted: Mon Nov 09, 2020 3:15 pm
by anamariboyes
Hi all.
I am trying to establish running TTHM's on my GC ECD.
I am new at this for this specific application.
I have a RXi-1ms column (30 m 0.32 mmID) and am following Standard Methods 6232.
I am having no luck with the oven profile 35C for 5 min, ramp 10C/min to 70C then 20C/min to 200C.
I am getting very fat peaks, almost look like sails!
Any help? I know I am missing the mark big time, I have little reference as to where to modify things.
Thanks!
Re: TTHM analysis on ECD- new to this method
Posted: Mon Nov 09, 2020 5:19 pm
by Steve Reimer
You may need to provide more information on your inlet conditions, etc.
Is this the column listed in the method? What is the film thickness?
Re: TTHM analysis on ECD- new to this method
Posted: Mon Nov 09, 2020 5:49 pm
by dblux_
Start with setting split ratio 5:1 in the inlet and as Steve said list complete method parameters incl. carrier flow.
Re: TTHM analysis on ECD- new to this method
Posted: Mon Nov 09, 2020 6:41 pm
by anamariboyes
Thank you for responding.
Column thickness is 1.0 um
No, this column is not listed in the method but has similar characteristics.
Injector conditions as follow:
Splitless
inlet 200C
split flow 50 mL/min
constant pressure @ 100kPa
I am using H2 as carrier/makeup
Makeup gas set to 15 mL/min
Detector temp 290C
I have been playing with oven ramps.
Looks like chloroform elutes at a low oven temerpature, around 35-40C.
I am getting fat ugly sail looking peak for chloroform and tricholroethane.
Re: TTHM analysis on ECD- new to this method
Posted: Mon Nov 09, 2020 9:22 pm
by dblux_
...
Injector conditions as follow:
Splitless
inlet 200C
split flow 50 mL/min
constant pressure @ 100kPa
If inlet is in splitless mode then why there is split flow ?
Try split mode 5:1.
I am using H2 as carrier/makeup
I always thought H2 can't be used as makeup gas in ECD. Should be N2 or Ar/Ch4
Besides you have constant pressure mode of flow and seems in your conditions carrier flow is 7.88 mL/min which is above optimal flow 2.2 to 3.2 mL/min
Re: TTHM analysis on ECD- new to this method
Posted: Tue Nov 10, 2020 5:17 pm
by James_Ball
Peaks like sails could indicate overloading of the column. I would also use constant flow mode if available instead of constant pressure.
What are the standard concentrations you are injecting?
We used to run these under method EPA501 using pentane extraction from 15ml sample. We used the Restek Rtx-502.2 column 0.53ID with 3um film, but that was 20 years ago, I would go with a 0.32 or 0.25 and split injections if doing it now.
Definitely want to use N2 makeup not H2 for ECD.
Re: TTHM analysis on ECD- new to this method
Posted: Fri Nov 20, 2020 9:48 am
by dblux_
Hi. Are you still there ? Ten days passed and no information whether your problem was solved or no.
BTW - have you implemented advices you gained exactly 6 years ago from forum ?
They were on GC/ECD determination of THM's as well.
Re: TTHM analysis on ECD- new to this method
Posted: Thu Dec 03, 2020 3:57 pm
by anamariboyes
Hello and thank you for your advice.
I do not run TTHM's regularly (obviously), it is a side work so when I come back to it, there are issues I am not foreseeing.
I have nobody else to branch out to.
I am currently pulled away, again from continuing my TTHM effort, so I have not re-visited.
Thank you for your support.