Dear all,

Sorry for this late answer, but as far as I remember, nobody pointed
out this possible source of bubbles in microfluidics where fluid is
driven by electroosmotic flow (or more generally in which high voltages
are used): the oxidation of water to form oxygen  bubbles. You can then
use a "sacrificial" electrochemical species such as hydroquinone that
will oxidize before water.
See Moini et al, Analytical Chemistry 1999, 71, 1658-1661


Hope this helps.

Kind regards

Niels Lion
Laboratory of Physical and Analytical Electrochemistry
(Prof. Hubert H. Girault)
Intitute of Chemical Sicences and Engineering
Swiss Federal Institute of Technology, Lausanne (EPFL)