11
Reference
Filling Hole
Reference
Filling Hole
Sensitive
Wire
Reference
Wire
Reference
Junction
Glass
Bulb
Glass
Bulb
Reference
Junction
Reference
Junction
Reference
Junction
Platinum or
Gold tip
Platinum or
Gold tip
Reference
Wire
Reference
Wire
Sensitive
Wire
Glass Body
pH Electrode
Plastic Body
pH Electrode
Plastic Body
ORP Electrode
Glass Body
ORP Electrode
Reference
Wire
ELECTRODE CONDITIONING
AND MAINTENANCE
PREPARATION PROCEDURE
Remove the protective cap.
DO NOT BE ALARMED IF SALT DEPOSITS ARE PRESENT. This is normal
with electrodes and they will disappear when rinsed with water.
During transport tiny bubbles of air may form inside the glass bulb
affecting proper functioning of the electrode. These bubbles can be
removed by "shaking down" the electrode as you would do with a
glass thermometer.
If the bulb and/or junction is dry, soak the electrode in
HI 70300
storage solution for at least one hour.
Note:
To prevent damage to the electrode, remove the pH
electrode from the solution before turning the meter off.
If the meter is OFF, detach the electrode from the meter
before immersing the electrode in the storage solution.
14
Alkaline Error
TEMPERATURE CORRELATION FOR 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 environments, short circuits and
static discharges
are detrimental to a stable pH reading.
The pH electrode's life also depends on the temperature. If constantly
used at high temperatures, the electrode life is drastically reduced.
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 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 characteristics.
-20 -20
-10
0 +10+20 +30+40 +50+60+70 +80+90
° C
-10
-10
Ω
-10
-10
-10
-10
Ω
2x10
9
1x10
9
2x10
8
1x10
8
2x10
7
1x10
7
-20 -10 0
+
10
+
20
+
30
+
40
+
50
+
60
+
70
+
80
+
90
°C
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
