Siemens Rapidlab 1200 - Page 49

Rapidlab 1200 Operator’s Guide: System Overview and Intended Use 1-29
02087462 Rev. V
During analysis, a membrane potential develops as a result of the interaction of
the analyte (ion) at the membrane. The membrane potential is related to the
amount of substance being measured in the sample. The half-cell potential in the
sensor consists of the inner reference element potential plus the membrane
potential.
Figure 1-28 Electrode Elements
The equation for calculating electrochemical cell potential can be expanded to
include the inner reference element and the membrane potential of the ISE.
E
cell
= (E
ref elmt
+ E
memb
) - (E
ref
+ E
lj
)
where
E
cell
= electrochemical cell potential
E
ref elmt
= potential of the ISE inner reference element
E
memb
= potential of the ISE membrane
E
ref
= reference electrode half-cell potential
E
lj
= liquid junction potential
1 Voltmeter
2 Potassium chloride solution
3 Inner element of the reference electrode
4 Liquid junction potential develops
5 Ion-selective membrane
6 ISE inner reference element
7 A fixed electrolyte solution