Dear Jeroen,
consider uncovered by gold chromium layer (or what else are you using as
diffusion
barrier ) underneath or / and at electrode edges and thus corrosion, esp. at low
frequencies. HCl and NaOH can be generated locally. Erosion also could be caused
by ultrasonics...
(e.g.   Hagedorn, R., Korlach, J. and Fuhr, G. (1998) Amperometric pH
regulation.
Flexible tool for rapid and precise temporal control over the pH of an
electrolyte
solution. Electrophoresis 9, 180-186.)

Best wishes
S. Fiedler
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
 Dr. Stefan Fiedler
 Fraunhofer - Institut fuer
 Zuverlaessigkeit u. Mikrointegration
 Gustav-Meyer-Allee 25
 D-13355 Berlin
 Germany

 Telefon +49 (0) 30/46403-217
 Telefax +49 (0) 30/46403-271
 e-mail  fiedler@izm.fhg.de
 http://www.izm.fhg.de

Jeroen Nieuwenhuis wrote:

> Dear all,
>
> I am trying to measure the impedance of a 1% NaCl solution using 50 um x 150
> um gold electrodes (thickness 0.6 um) in a microchannel and the electrodes
> dissolve in about 40 minutes(!).
>
> I used very pure NaCl and distilled water to make the solution. I use a
> sine-wave generator to make a 50 mV AC voltage (offset oV) and I measure the
> current using an transimpedance-amplifier with a 100k resistor. Nor the source
> nor the read-out electronics seems to generate a DC value current.
>
> Does anybody have a suggestion what is going on? To the best of my knowledge
> nothing should happen when the AC voltage used is less than about a volt.
>
> Regards,
> Jeroen Nieuwenhuis
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