The extraction process

Regardless of the conditions and the technique used, the profile of the extracted quantity is always the same according to the progress of extraction (see graph):

  1. At first, the compound to be extracted is solubilized by the extractant – the extracted quantity increases quickly with the extraction duration
  2. Then a plateau is observed – the extraction process is controlled by diffusion (and sometimes by desorption in the case of certain solid matrices).

Reaching the plateau does not necessarily mean that the compound has been entirely extracted. On the other hand, it is important to understand the shape of the curve for an intended application and to choose an appropriate extraction duration.

graph of the extraction, with the progress of the extraction on the abscissa, and the quantity extracted on the ordinate. The curve is increasing and linear in the first phase. In this phase the extraction is controlled by the solubilization. Then follows a transition phase, where the speed of extraction decreases. Finally, the curve is again linear in a third phase, where the extraction is controlled by diffusion (as well as desorption?).
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