Methods Based on the Change in Bulk Concentration

An obvious way to determine the amount of a substance adsorbed on the surface is to measure the resulting change in its bulk concentration. This is equivalent to measuring adsorption from the gas phase by determining the decrease in partial pressure of the relevant gas. 

The sensitivity of such methods depends on the ratio between the volume of the solution and the surface area of the electrode. A typical electrochemical cell has about 10 cm of solution per cm of surface area. In view of the very small amounts of material needed to form a monolayer, there is a need to increase the sensitivity of this type of measurement, by using a high-surface-area electrode and low concentration in solution. The surface-to-volume ratio can also be increased by using porous electrodes or by rolling up an electrode in a minimum volume of solution. Care must be taken, however, to ensure that potential control and uniformity are maintained in this type of measurement, remembering that the extent of electrosorption is potential dependent. 

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