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TitraLab
®
Direct ISE
measurement
method -
definition
Measurement method using a selective electrode (ISE) of the ion you
want to determine the concentration.
In a Direct ISE measurement method, you must calibrate the ISE
electrode using 1 to 9 standard solutions of known concentration.
Refer to "Electrode calibration (ISE)", page
If a calibration with 3 to 9 standards is carried out, E
determined by non linear regression using the following equation:
0
E = E
• E = potential measured in the sample,
0
• E
= electrode standard potential,
• S
= electrode response slope (sensitivity) at 25°C,
25
• T = temperature of the solution in K,
• T
= 298.16 K,
25
• C = concentration of sample,
• C
= detection limit concentration. It is the "experimental detection
0
limit of the electrode regarding the species under study " .
If a 1-point calibration is performed, only E
takes the S
sensitivity from the last calibration done or takes the the-
25
oretical value which depends on the ion valency (for example:
-59.16 mV for a positive monovalent ion). C
If a 2-point calibration is performed, E
the same equation as above but with C
perform a 2-point calibration in the linear response zone of the ISE
electrodre.
log (C)
Refer to "Direct ISE measurement method - notes", page
TitraLab 870 Reference Manual
+ S
x T/T
(-log (C+C
25
25
0
and S
= 0. It is recommended to
0
C
0
-7
-6
-5
-4
-3
109.
0
, S and C
)) where:
0
0
is calculated. The TIM870
is equal to 0.
0
are calculated using
25
E (mV)
0
E
90
60
30
0
-30
-90
-120
-150
-180
-2
-1
96.
are
0
Page 95
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