What is meant by the term "salting out" in the liquid-liquid extraction procedure?
The term "salting out" in the context of liquid-liquid extraction refers to a technique used to separate compounds based on their solubility in a solvent. It involves the addition of a high concentration of a salt into the solution to decrease the solubility of certain compounds.
To understand salting out in liquid-liquid extraction, we first need to know the concept of solubility. Solubility refers to how well a solute (substance being dissolved) can dissolve in a solvent (substance doing the dissolving). Different compounds have different solubilities in specific solvents.
In liquid-liquid extraction, two immiscible liquids (liquids that do not dissolve in each other) are used to separate compounds. The target compound is usually dissolved in an organic phase, while the unwanted impurities or interfering compounds are present in an aqueous phase.
To enhance the separation, a high concentration of salt, such as sodium chloride (NaCl), is added to the solution. When the salt dissolves, it breaks into ions (Na+ and Cl-) that occupy space in the solution, reducing the available space for the organic compounds to dissolve. This decrease in solubility of the organic compound causes it to separate from the aqueous phase and move into the organic phase.
The salt effectively "salts out" the organic compound from the aqueous phase, making it easier to extract it using liquid-liquid extraction. The phase separation can be achieved by centrifugation or decantation, allowing the two phases to separate based on their densities.
In summary, salting out in liquid-liquid extraction involves adding a concentrated salt solution to decrease the solubility of the target compound in the aqueous phase, causing it to separate and redistribute itself into the organic phase for easier extraction.