Chromatography Forum

I'm running an Agilent 6890 GC with an ECD detector for pesticide testing, and it just started being very inconsistent with the response readings for some pesticide compounds. I even ran a new calibration curve, and I put my ICV to rerun a couple of times to make sure it was consistent, but it was all over the place, sometimes high sometimes low, and never consistent.

The GC basically went from running a calibration that would be good for months at a time, to running a calibration every time the liner was changed.

This has been going on for a few weeks, but before I could just run a new calibration then my samples and it would be fine for that entire run, but now it seems like even that wont work. I have some new columns on the way, so hopefully that will fix the issue, but I was wondering if anyone on here has any further insight as to what could possibly be causing this problem.

Any help/advice would be appreciated. Thanks for your time.

Assuming it's not a packed column, have you tried trimming it? Lopping off ~half a meter at the detector end (or both ends if you have dirty samples) will often work wonders for peak shape. If your peak shape is good, start checking the injector for problems, leaks, clogs, bad septum, etc.

What kind of matrix are your samples in? As DR said above, the best place to start is with simple column maintenance and see how you get on from there.

DR wrote:
Assuming it's not a packed column, have you tried trimming it? Lopping off ~half a meter at the detector end (or both ends if you have dirty samples) will often work wonders for peak shape. If your peak shape is good, start checking the injector for problems, leaks, clogs, bad septum, etc.

Peak shape looks good, its just the area count/peak size that is inconsistent. We haven't trimmed the column, but it looks like a new one came in over the weekend so we're going to put in a brand new one.

AaronAIT wrote:
What kind of matrix are your samples in? As DR said above, the best place to start is with simple column maintenance and see how you get on from there.

We run our samples in hexane. Yeah, we're putting in a new column. Hopefully that resolves the issue.

This is far more likely to be an inlet problem than anything to do with the column - if the column is bad it stays bad from run to run. What is your inlet maintenance schedule - when last did you change septum and liner ? Have you checked for leaks ? Are you sure that the autoinjector is working properly ?

Peter

Peter Apps wrote:
This is far more likely to be an inlet problem than anything to do with the column - if the column is bad it stays bad from run to run. What is your inlet maintenance schedule - when last did you change septum and liner ? Have you checked for leaks ? Are you sure that the autoinjector is working properly ?

Peter

Problem has been solved! It was indeed an inlet leak! Some loose connections were found, and in trying to fix the leak the weldment ended up breaking so that had to be replaced as well. Hopefully this behavior description helps someone else in the future if they come across this post.