Ionode IJ pH V5.1 - Manual (Page 32)

Ionode IJ Instruction Manual 32
way pH does not characterize the buffering
capacity.
5.1.1. Output
ORP values are determined by measuring the
potential difference between an inert sensing
half-cell and a reference half-cell as in pH. The
sensing half-cell acts as a platform for electron
transfer to or from the sample. The sensor does
not undergo oxidation or reduction. It is typically
platinum. Gold (Model IJAu) and Silver (Model
IJAg) sensors can also be used. The former is
substantially inert, whereas the latter responds
to silver and halide ions, and can be used for
silver
titrations. The standard hydrogen
electrode (SHE) is the reference from which all
formal redox potentials are determined and has
been assigned an arbitrary half cell potential of
0.0 mV. However, it is fragile and impractical for
routine laboratory use. Therefore, Ag/AgCl and
saturated calomel (SCE) reference electrodes
are used. Earlier literature often used SCE. The
use of SCE is now rare because it contains
mercury. The voltages of the different reference
electrodes can be interrelated (see
Table 6 ).
The IJ64 uses an Ag/AgC/saturated KCl
reference electrode.