Hanna Instruments ph 301 User Manual
91
90
Typical Electrode Life
Ambient Temperature 1- 3 years
90 °C Less than 4 months
120°C Less than 1 month
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 significant
depends upon the composition of the glass.
This interference is the alkaline error and
causes the pH to be underestimated. Hanna's
glass formulations have the indicated char-
acteristics.
with readings in alkaline solutions; the pH at
which the interference starts to be significant
depends upon the composition of the glass.
This interference is the alkaline error and
causes the pH to be underestimated. Hanna's
glass formulations have the indicated char-
acteristics.
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
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
0.14
0.20
0.10
0.18
0.29
0.40
TEMPERATURE-RESISTANCE CORRE-
LATION 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 for the reading to stabilize if the resis-
tance is higher. In addition, the response
time will suffer to a greater degree at tem-
depends on the temperature. The lower the
temperature, the higher the resistance. It takes
longer for the reading to stabilize if the resis-
tance is higher. In addition, the response
time will suffer to a greater degree at tem-
-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
peratures 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 hours.
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 hours.
For these reasons high humidity environ-
ments, short circuits and static discharges
are detrimental for a stable pH reading.
ments, short circuits and static discharges
are detrimental for a stable pH reading.
The life of a pH electrode also depends on
temperature. If constantly used at high tem-
peratures, electrode life is drastically reduced.
temperature. If constantly used at high tem-
peratures, electrode life is drastically reduced.
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