User Guide

25
24
Typical Electrode Life
Ambient Temperature 1- 3 years
90 °C Less than 4 months
120°C Less than 1 month
High concentrations of sodium ions interfere
with readings in alkaline solutions; the pH at
which the interference starts to be signifi-
cant depends upon the composition of the
glass. This interference is the alkaline error
and causes the pH readings to be underesti-
mated. Hanna's glass formulations have the
indicated characteristics.
Alkaline Error
1.0 Mol L
-1
Na
+
0.1 Mol L
-1
Na
+
Sodium Ion Correction for the Glass
at 20-25°C
Concentration pH Error
13.00
13.50
14.00
12.50
13.00
13.50
14.00
0.10
0.14
0.20
0.10
0.18
0.29
0.40
TEMPERATURE-RESISTANCE
CORRELATION FOR HANNA
pH SENSITIVE GLASS
The resistance of glass electrodes partially
depends on the temperature. The lower the
temperature, the higher the resistance. It
takes longer time for the reading to stabilize
if the resistance is higher. In addition, the
response time will suffer to a greater degree
at temperatures below 10°C.
Since the resistance of the pH electrode is
in the range of 200 Mohm, the current across
the membrane is in the pico Ampere range.
Large currents can disturb the calibration of
the electrode for many hours.
For these reasons high humidity environ-
ments, short circuits and static dis-
charges are detrimental for a stable pH
reading.
The pH electrode's life also depends on the
temperature. If constantly used at high tem-
peratures, the electrode life is drastically
reduced.
-
20
-
20
-10
0 +10+20 +30+40 +50+60+70 +80+90
°
C
-10
-10
Ω
-10
-10
-10
-10
2x10
9
1x10
9
2x10
8
1x10
8
2x10
7
1x10
7