Chlorinated Pesticides Question on Agilent 8890


Our lab has an Agilent 7890 ECD that has been running chlorinated pesticides for several years.  We have a new 8890 and I'm tasked with getting it online.  After discovering we did not have deactivated metal inlets, and Endrin and pp DDT were being completely broken down into byproducts, we installed unimetal inlets and fixed that.

Now, the DB-5 column gives great decomposition results (<15%), but the DB-1701 column is overlapping a ghost peak on top of the pp DDD peak making all decomposition readings >25% even after a full maintenance with seals, liners, septa replaced and a full cleaning as per Agilent's online cleaning recommendations.  

This ghost peak is also present on the 7890's DB-1701 column, but it is downstream of pp DDD and does not overlap so its not an issue.

I have changed ramp temperatures and hold times in order to separate these two peaks, without much result.  Putting a 2 minute hold 30 degrees before the boiling point of pp DDD did moved the peak around within the larger overlapping peak but it did not separate them.  Whatever this ghost peak is, it seems to have the same physiochemical properties as pp DDT, since it travels with it in the column, no matter what condition I have changed in the ramp.

I've had multiple suggestions here, from changing the ramps (which I did) to changing to a completely different column than a 1701.  But I'd like to hear from someone whom has maybe had this experience and can offer other suggestions as to how to approach this problem.  

Our ramp is as follows:

Ramp    Rate   Value    Hold   RT

1             15       150        0     9.33

2              4         260     10     46.83

3              20       280        4     51

This puts me at about an hour per sample time, which is about where we need to be to get samples out the door.

Any suggestions you guys have are welcome!  Thanks for your help.

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