Hanna Instruments HI 8614N User Manual

Page 11

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.

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 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.

TEMPERATURE-RESISTANCE CORRELATION

FOR HANNA

FOR HANNA pppppH 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 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 °C (77 °F).

Typical Electrode Life

Ambient Temperature

1 – 3 years

90 ºC

Less than 4 months

120 ºC

Less than 1 month

TEMPERATURE CORRELATION

FOR

FOR pppppH SENSITIVE GLASS

H SENSITIVE GLASS

1.0 Mol L

-1

0.1 Mol L

-1

Sodium Ion Correction for the Glass at 20-25 ºC (68-77°F)
Concentration

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

This manual is related to the following products:

HI 8615N