Jessica,
As discussed yesterday, we use this same set up and battled for over 12 months to get the assay working. We eventually found it was the mobile phase, and an inability to recycle it (we never found out why). When we don't recycle we get very stable retention times throughout the run. recycling produced huge drift within the run. We can still re-use the mobile phase a second and even third time, just not recyle during a run! its bizarre and Chromsystems said it must be something specific to our instrumentation. no one I have spoken to has been able to come up with an answer. We do now run urine mets in small batches weekly and it works very well with this set-up. Our EQA has been very good so far. The ECD should be fine if it has been serviced. Just keep the reference electrode fully topped up with saturated KCl to keep the background low. I have sent you our detector settings that work for us.
We do see interference in the internal standard sometimes as John pointed out, but all in all it works very well.
Good luck!
Lisa
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