Roche Cedex Bio User Manual

Roche Diagnostics
C-32
Operator’s Manual · Version 3.4
8 Data analysis methods Cedex Bio analyzer
ISE measurements
Test principle
An Ion-Selective Electrode (ISE) makes use of the unique properties of certain
membrane materials to develop an electrical potential (electromotive force, EMF) for
the measurements of ions in solution. The electrode has a selective membrane in
contact with both the test solution and an internal filling solution. The internal filling
solution contains the test ion at a fixed concentration. Because of the particular
nature of the membrane, the test ions will closely associate with the membrane on
each side. The membrane EMF is determined by difference in concentration of the
test ion in the test solution and the internal filling solution. The EMF for a specific
ion in solution develops according to the Nernst equation.
Nernst equation
Electrolyte activity is measured by determining the potential difference between the
measurement and reference electrodes. The relationship between the potential
difference and the ionic activity is given by the Nernst equation.
If the ionic strength of the calibrating solution chosen is equal to that of the sample,
the electrode system can be calibrated with acceptable accuracy in terms of the ionic
concentration instead of the activity.
The potential measured is directly related to the concentration.
Calculation of Sol 1 factor
Potential difference between the measurement and reference
electrodes.
Standard potential of the electrode assembly. (Depends on the
construction of the electrode.)
Electrode slope (Nernst Factor).
Ionic activity of the electrolyte being measured.
EE
0
Sa
i
log⋅+=
E
E
0
S
a
i
Slope in mV/dec
Known concentration of ISE Solution 1.
Electrode potential of ISE Solution 1 in mV.
Electrode potential of the ISE calibrator in mV.
Known concentration of ISE Solution 1.
Calculated concentration of ISE Solution 1.
ISE Solution 1 factor.
C
sol1 calc
C
sol1
10
E
sol1-1
E
ISEcal-1
–
S
---------------------------------------- -
C
sol1
10
E
sol1-2
E
ISEcal-2
–
S
---------------------------------------- -
⋅+⋅
2
---------------------------------------------------------------------------------------------------------------------------------------
=
Sol1Factor
C
sol1 targ
C
sol1 calc
-------------------- -
=
S
C
sol1
E
sol1
E
ISE cal
C
sol1 targ
C
sol1 calc
Sol1Factor

Roche Cedex Bio Specifications

General

Brand	Roche
Model	Cedex Bio
Category	Measuring Instruments
Language	English