Impact Of Stirring; Impact Of Coexistent Ions - Horiba Scientific 6560S-10C Instruction Manual

If the temperature of the sample solution in measurement differs from the
temperature of the standard solution in calibration, perform calibration
again.
When the electrode is moved to a place that has a different temperature,
wait until the temperature of the electrode becomes same as the
temperature of that place before using the electrode.


Impact of stirring

The impacts on the measurement of the electromotive force by stirring the
sample solution are, for example, slow response, inability to measure the
low concentration solution, and the change of the electrode potential.
It is best to control the stirring speed so that the stir bar will rotate 3 or 4
turns per second.
If swirling occurs on the surface, the stirring speed is too fast. Reduce the
speed to a level where swirling does not occur.


Impact of coexistent ions

Although ion selective electrodes have good selectivity with respect to the
ions to be measured, they may react to the other ions.
The ions which interfere the measurement of the concentration of the ions
to be measured are called "interfering ion". Therefore, when using the ion
electrode method, it is important to know the effects of coexistent ions and
take measures to avoid them.
The impact that coexistent ions will have on electromotive force
measurements with the ion electrode method can be predicted from the
extent to which they react with the structure material of the ion selective
membrane. For example, in the case of solid membrane electrodes,
coexistent ions that may form compounds with poor solubility or may form
complex salts with the structure material of the ion selective membrane are
likely to have a significant impact, whereas in the case of liquid membrane
electrodes, coexistent ions that may form an ion association with the
components of the ion selective membrane are highly likely to have an
impact.
65