TTHM analysis on ECD- new to this method

[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!

[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?

[dblux_]

Start with setting split ratio 5:1 in the inlet and as Steve said list complete method parameters incl. carrier flow.

[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.

[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

[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.

[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.

[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.