I am using a coulometric electrochemical cell (ESA 5011) at E1 -150mV, E2 +200mV. When I inject on a dopamine standard made in mobile phase or water I get a normal looking chromatogram with a standard looking void and then elution of peak at 4 minutes. However, when I inject a biological sample (dialysate) or standard made in artificial CSF (basically NaCl, KCl, CaCl2, glucose) I get a very strong negative deflection that only returns to baseline within 6 minutes if I autozero.

Is there a way i can modify the electrochemistry (change the potentials on E1 or E2?) to prevent the trace going off scale like this?

thanks for any help
nick