ghost peak at LC

[id4hplc]

I ran monoamine detection with HPLC-ECD.
I continuously saw monoamine peaks when I loaded buffer only (without any monoamine powder to setup the standard quantification). The HPLC water, Ringer sand mobile phase do not show any peaks. However, When I load stock and dilution buffer only, I see the monoamine peaks at the correct time points. I really don't understand why the monoamine peaks appear at the chromatogram even I did not load microdialysate or monoamine powders.

Would you give any clues to solve this problem?
Thanks

[tom jupille]

The first thing that comes to my mind is contamination (e.g. from dust floating around the lab). If this were my problem, I would try making up the buffers in a different lab at least once.