Research Applications

Conductivity

e-corder with Chart software can monitor solution conductivity (which is related to the total ionic concentration) signals with a suitable electrode and meter.

We supply the:

And suitable electrodes:

Many other brands of conductivity cell and meters are also suitable for use with e-corder. The vast majority of 'conductivity cells' (the correct name for a 'conductivity electrode') comprise a pair of platinum plate electrodes coated with platinum black - do not try to 'clean' the electrodes to make them shiny! The platinum black coating (finely divided platinum) provides a catalytic surface for the rapid recombination of hydrogen and oxygen to reform water - otherwise formation of bubbles can occur because of the electrical currents flowing through the electrodes and these would contribute to inaccurate measurements.

An oscillating potential is placed on the electrodes and the resulting AC current measured, and from this the electrical resistance of the sample solution determined. Most meters have a fixed AC frequency but more expensive models may allow the user to adjust the frequency (usually between 50 - 2000 Hz) in order to optimise the signal to get quieter readings. The cell is first calibrated by measuring a solution of known composition (say a 0.1 mol/L potassium chloride solution) at a fixed temperature.

In traditional studies the 'Cell Constant' (k) of the electrode determined. The value of 'k' is affected by the surface area of, and the distance between, the pair of platinum plate electrodes. A pair of electrodes exactly 1 cm apart, each of area 1 cm2, would have k = 1. Larger electrodes and/or smaller separation would give a smaller k value, while conversely smaller electrodes and/or a larger separation would give a larger value. The exact k value is determined by measuring a calibration solution of known conductivity.

Electrodes with a k value of approximately 1 are usually the most useful for general laboratory work. Electrodes of k = 0.1 are more useful for working in solution of very low ionic concentration (such as highly purified water) while electrodes of k = 10 are more useful when very high ionic concentrations are encountered (such as with sea water).

When using e-corder it is merely necessary to enter the value of the calibration solution in the Chart software Units Conversion dialog. This will automatically calibrate the electrode without having to calculate 'k' as a separate entity.



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