36
The temperature limit for the
HI 1230B
and
HI 1618D
is from 0 to 80 °C
with optimum measurements between 20 and 40 °C. 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 to 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.
The
HI 1618D
and
HI 1230B
are specified for a pH range of 0 to 13 pH.
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.
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
1.0 Mol L
-1
Na
+
0.1 Mol L
-1
Na
+
Sodium Ion Correction for the Glass at 20
-
25
º
C (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
