Applications of direct conductimetric measurements

Direct measurement of conductivity is potentially a very sensitive procedure for measuring ionic concentrations, but it must be used with caution since any charged species present in a solution will contribute to the total conductance. 

Conductimetric measurements can also be used to ascertain the end-point in many titrations, but such use is limited to comparatively simple systems in which there are no excessive amounts of reagents present. Thus, many oxidation titrations which require the presence of relatively large amounts of acid are not suited to conductimetric titration. Conductimetric titrations have been largely superseded by potentiometric procedures (see Chapter 15), but there are occasions when the conductimetric method can be advantageous.14 

Purity of water. The purity of distilled or de-ionised water is commonly checked by conductimetric measurements. The conductivity of pure water is about 5 x 10-8Q-1 cm-1, and the smallest trace of ionic impurity leads to a large increase in conductivity. Conductimetric monitoring is employed in laboratories to check the operation of ion exchange units producing de-ionised water, and finds similar industrial application where processes requiring the use of very pure water (e.g. manufacture of semiconductors) are carried on. 

There are important industrial applications, such as the control of boiler feed water and of boiler blow-down in large steam-generating plants to check the 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

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