black column at detector?

[Nbullard]

We have been running a method where the column will turn black or looks dirty- not completely black- at the detector end. I thought that usually the front end of the columns got dirty and don't know how to explain this. It's an ECD detector at 300C. I was thinking 300 wasn't hot enough to cause coking in the column but I really don't know. Anyone have any suggestions on what to check?

I'm also not sure if it's a GC issue or sample prep/extraction. This is for EPA method 508.

[rb6banjo]

I don't work with ECD's but is it possible that the column is up into the detector too far? With Agilent flames, installation involves running the column up into the detector as far as it will go, and then just barely backing it off so it doesn't touch the metal. I've had those sit at 300 °C for 2 years at a time and not show any charring.

[Nbullard]

Thanks. That may be the issue. I found this explaining how to install the column. https://www.agilent.com/cs/library/Supp ... F03045.pdf

1. We are using straight liners on a micro ECD which it says not to
2. We were doing the 70 mm from bottom of column nut which is only for small id on indented liner, and it says to just extend 1 mm on straight liners.

So I think extending the column too far may be it.