Temperature correlation, 0 mol l, 1 mol l – Hanna Instruments HI 4521 User Manual
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107
TEMPERATURE CORRELATION
TEMPERATURE CORRELATION
TEMPERATURE CORRELATION
TEMPERATURE CORRELATION
TEMPERATURE CORRELATION
FOR
FOR
FOR
FOR
FOR pppppH SENSITIVE GLASS
H SENSITIVE GLASS
H SENSITIVE GLASS
H SENSITIVE GLASS
H SENSITIVE GLASS
Typical Electrode Life
Ambient Temperature
1 – 3 years
90 ºC (194 ºF)
Less than 4 months
120 ºC (248 ºF)
Less than 1 month
Alkaline Error
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 called alkaline error and
causes the pH to be underestimated. Hanna’s glass formulations have the indicated characteristics.
1.0 Mol L
-1
Na
+
0.1 Mol L
-1
Na
+
Sodium Ion Correction for the Glass at 20-25 ºC (68-77 ºF)
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
The resistance of glass electrodes partially depends on the temperature. The lower the temperature, the higher the
resistance. It takes more 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 25 ºC (77 ºF).
Since the resistance of the pH electrode is in the range of 50 – 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.