Hanna Instruments HI 9017 - Manual (Page 53)

53
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 TEMPERATURE-RESISTANCE CORRELATION TEMPERATURE-RESISTANCE CORRELATION TEMPERATURE-RESISTANCE CORRELATION TEMPERATURE-RESISTANCE CORRELATION
FOR HANNA FOR HANNA FOR HANNA FOR HANNA FOR HANNA pppppH SENSITIVE GLASS H SENSITIVE GLASS H SENSITIVE GLASS H SENSITIVE GLASS H 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 for 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