DDT and Endrin breakdown?

[dalarie]

Hi
I was wondering if anyone has problems with endrin/ddt breakdown on Agilent 6890? I have had this problem for 2 years and cannot solve it. I have changed inlet body, tried new liners, changed gas lines lowered injection temperature from 275 to 250 and the only thing that works is using new liners. And that only lasts two days maximum before I have to perform maintenence again and I am running relatively clean samples. Sometimes endrin breaks down right after running standards.
My second source standard and lowest standard read perfect.

It is too expensive to use new liners every few days.

Does any one have any other suggestions?

Thanks for your help.

[chemwipe]

Dalarie-

You must be running pesticides, right?

My previous experience with running pesticides dictated changing the siltek liners every day. Yes, EVERY DAY. Unless you want to waste time with an endrin/DDT solution that keeps breaking down, change your liner, and change your inlet seal while you're at it. You might also want to consider trimming off 1 to 2 feet from the injector side of the column.

Are you running a calibration curve daily?

It is too expensive to use new liners every few days.

What kind of liners are you using? If ordering liners is too expensive, you can try what I used to do.

I used siltek liners and regenerated them by heating them (in a hood) in a solution of 5% DMDCS in toluene, otherwise known as Sylon-CT.

Hope that helps!

John

[dalarie]

Hi,

Thanks for your response. yes I run pesticides at very low concentrations (1.5 ppb) I change liners/trim column/change gold seal and scrub inlet every time I do maintenence.
I also have an extensive cleaning process that consists of boiling in nitric acid and using silanizing agent.
Yes, i usually have to re-calibrate every maintenence.

Oh well, its good to hear that I am not alone. I guess I will use new liners and report samples that don't have any hits.

thanks for your help
D

[Bigbear]

Scrubbing the inlet? Are you using the Agilent paper for reference?
If so note that they consider the inlet weldment to be a consumeable. You may have reached that point.
I do not scrub my inlet until changing liners has no affect.