Topics - Displacement
The term displacement, when used in the chromatographic sense, described the process where one solute interacts more strongly with an active surface than another and so removes it (displaces it) and occupies its original active sites. Displacement
is one of the three basic methods of chromatographic development. As a sample mixture enters an adsorption column, the first available adsorption sites will immediately be occupied by the most strongly interactive solute. As the sample band continues its movement down the column, the next available sites will be occupied by the next most interactive solute. In this way, all the components will array themselves along the column in order of their decreasing interactivity with the adsorbent. The separation is developed by introducing another substance (called the displacer) that interacts more strongly with the adsorbent than any of the solutes. On coming in contact with the solute most strongly held, it will displace this into the mobile phase and occupy the sites. The strongly active solute will then displace the next solute and occupy the sites with which it was interacting. Thus, the displacer forces the adsorbed solutes along the column each solute displacing the one in front until they are eluted in the same order in which they were adsorbed. Displacement chromatography has the great disadvantage that it can not elute solutes discretely and each solute will always be contaminated by its neighbors.