Chromatography Forum

Hi,

Can anyone help me with a breakdown problem? I am running pesticides on an Agilent 5890 GC with dual ECD's. I run a DDT/Endrin breakdown check. The DDT breakdown is very low. The endrin breakdown is between 30-60%. Our requirement is <15% breakdown. I've checked for leaks at the inlet, y-splitter, and the detectors and found none. I baked out the detectors at 375 degrees celsius overnight and this did not improve the breakdown. A different column was installed. The breakdown is still high. The injection port and everything I can think of was cleaned.

Has anyone had a similar problem? Or can anyone provide me some things to try?

I'd appreciate any help you can give.

Are you using deactivated liners and have you tried replacing it?

DDT is quite stable so a dirty liner would have much more impact of an impact on Endrin breakdown. This also goes for anything else in your system which could be dirty, although on an ECD I can't think of much you haven't checked other than the filters on the carrier gas line.

The liner was changed. The filters were not. I've ordered some new filters. I'll let you know how it goes.

This instrument runs PCB's also and does not require a degradation check, so I may just run those until the filters come in.

Thanks.

Have you replaced the bottom seal in the injector? Endrin breakdown can occur there. Use a gold-plated seal. Also, consider using a single gooseneck (at the bottom) type of liner, which minimizes sample contact with the bottom seal in the first place. Also, although it seems counterintuitive to add a potential source of activity to the liner, using a small DEACTIVATED piece of glass wool in the liner can help by again preventing injected sample from reaching the hot metal bottom seal where Endrin is often degraded.

josette-

Do you use guard columns? Make sure you're using the Siltek Presstight connectors.

I agree also with the use of Siltek deactivated liners; however, I prefer to use the Siltek treated baseplates instead of the gold baseplates.

I also clean out my injection port with acetone every couple of days.

Hope that helps.

cw

You might want to rinse your split vent line. I have found this sometimes improves inlet performance significantly.

Best regards.

Have you tried another source for your endrin? I was chasing a similar problem which turned out to be that my stock endrin solution had ea and ek in it!

Thanks for all your help! I'm really impressed with the amount of feedback I've received as it is the first time I posted on this forum.

The problem is now fixed. The injector weldment was completely cleaned with DCM, MeOH, and hexane. Endrin breakdown is now low.

Again, thanks to everyone that responded!