THMs run thru ECD

[anamariboyes]

Hello everyone,

I am trying to develop a method to test for THMs in and ECD detector. I am having a hard time with some compounds co-eluting and was wondering if anyone has any tips to avoid this.
Thanks,
Anamari

[chemwomyn]

Hi there! If you are testing drinking water, take a look at EPA 551.1. This is a GC/ECD microextraction method for the testing of THMs and other DBPs in drinking water.

[anamariboyes]

Thanks chemwomyn,

I am basing my method on that specific EPA method but my retention times are not the same as the ones listed in the method and I am only looking for total THMs, not the full run like the method has developed.
I am using the same column they suggest (DB1) but my peaks start 20 minutes after theirs do (they start showing on minute 5), hence I think my heat ramps do not work well with the compounds at my settings.
For this reason I think peaks that should be separated are not because the temps are not right.

[AICMM]

anamariboyes,

1) When you say total THM's do you mean just the chloroform, DCBM, DBCM, and bromoform? Or do you mean as a lumped sum? Because, if the latter, you are asking for trouble.

2) 20 minutes for the first peak is WAY too long. Tell us a lot more about your column and your oven conditions, please, for us to be able to help you.

3) A db-1 is not where I would have started.

Best regards,

AICMM

[fsistere]

Hi

In my work i analyze THM's in drinking water. It's a rutine work.
I use a DB-624 or HP-624 column (30m x 0.32mm x 1.8um). They work good for volatile compounds.
Injection.- 250ºC; split 1:30
ECD.- 250ºC
Constant flow.- 1.8ml/min
Tª program.- 35º(1min). ramp 8ºC/min to 170º(0min). ramp 30º/min to 280º(2min).

I do a liq-liq extraction. You can do also headspace or Purge & trap.

[sbull]

Went through this same thing last year, developing a method from scratch using USEPA 551.1 as a starting point. I found I had to be very careful to maintain separation of bromodichloromethane from a potential co-eluter. I use a Perkin-Elmer Clarus 580 and Restek Rxi-1ms and Rtx-1301 columns. The run time is fairly long, almost 41 minutes. 20 minutes is definitely too long, just be sure to keep chloroform out of your solvent front and don't lose your surrogate on the back end. From my experience with drinking water, chloroform is usually the high offender before any of the other compounds. Good luck