Introduction - Determination of Anions in Natural and Treated Waters - page 24

1.1.6.2 Potentiometry
This technique has been applied to the determination of iodide and free cyanide in non
saline waters and nitrate in aqueous precipitation.
1.1.6.3 Chronopotentiometry
This technique has been applied to the determination of chloride in seawater.
1.1.6.4 Amperometry
This technique has been applied to the determination of nitrate and nitrite in non saline
waters and nitrite in trade effluents.
1.1.6.5 Anodic stripping voltammetry
This technique has been applied to the determination of selenite, hypochlorite, chlorite
and phosphate in non saline waters, and polysulphide, sulphate and thiosulphate in waste
waters.
1.1.6.6 Cathodic stripping voltammetry
This technique has been applied to the determination of iodate, iodide, nitrite and
chloride in non saline waters and iodide and nitrate in seawater and sulphide in waste
waters.
1.1.7 Ion selective electrodes
Ion selective electrode technology is based on the simple measuring principle consisting
of a reference electrode and a suitable sensing or indicator electrode sample solution (for
the ion being dipped) dipped in the sample solution and connected by a sensitive
voltameter. The sensing electrode responds to a difference between the composition of
the solution inside and outside the electrode and requires a reference electrode to
complete the circuit.
T he Nerst equation, E = E 0 + S log C , which gives the relationship between the activity
or concentration (C) contains two terms which are constant for a particular electrode.
These are E 0 (a term based on the potentials which remain constant for a particular
sensing/reference electrode pair) and the slope S (which is a function of the sign and
valency of the ion being sensed and the temperature). In direct potentiometry, it has to be
assumed that the electrode response follows the Nernst equation in the sample matrix and
in the range of measurement. E 0 and slope are determined by measuring the electrode
potential in two standard solutions of known composition and the activity of the ion in
the unknown sample is then calculated from the electrode potential measured in the
sample.
Reference electrodes of interest to the water chemist are of two types—single function