posted on 2023-12-22, 01:05authored byTatsunori Kishimoto, Kentaro Doi
Glass nanopores are
known to provide proton selectivity in ionic
current conditions in which silanol groups that fill glass surfaces
support proton conduction along the surfaces in aqueous solutions.
Negatively charged glass surfaces furthermore exclude anions from
the glass nanopores. Therefore, glass electrodes are often used for
the probes of pH sensors. We focused on the ion selectivity and ionic
current rectification of glass nanopores. In this study, we propose
triple-barreled glass microelectrodes that enable us to measure proton
concentrations at local points with spatial resolution of the tip
diameter. The glass microelectrodes consist of three capillaries for
the working, counter, and reference electrodes filled with electrolyte
and pH buffer solutions. A pH 1.68 buffer and KCl solution as a supporting
electrolyte are maintained in a glass capillary for the counter electrode,
and KCl solutions are in the working and reference electrodes. In
galvanostatic current conditions, potential differences are measured
in sample solutions. The potential difference is caused by the proton
concentration gradient and proton-selective conduction, which is known
as electrodiffusioosmosis. The ionic current is rectified due
to the proton selectivity of the glass capillary, and as a result,
the conductivity reflects the relative difference of pH values, ranging
from 1.68 to 10.01 units. The temperature dependence of pH values
is also investigated in the range from 303 to 333 K. The proposed
glass microelectrodes achieve a pH resolution of 1.39 V/pH, which
is much higher than the Nernst limit.