What Are Those Forces During SPE?

Non-Polar Interaction, the interaction between a non-polar functional group on a target compound and a non-polar sorbent, which is better reflected in a polar solvent environment, especially in a water environment. Also known as hydrophobic interactions, such as the interaction between phthalate compounds and C18 in aqueous environments.

Polar interaction, the interaction between the polar functional group on the target compound and the polar functional group on the adsorbent. Polar interactions include Hydrogen Bonding, Dipole/Dipole, Induced Dipole/Dipole, π-π (Pi-Pi) and many other interaction forces. This force can be better reflected in a weakly polar or non-polar solvent environment.

Ion Interaction refers to an attraction force (known as Coulomb force) between target compounds with a positive/negative charge and absorbents with the opposite charge.

Secondary Interaction, for reversed-phase silica bonds and adsorbents, the residual silanol groups on the surface of the particles will interact polarly with polar compounds, and some of the silanol groups will undergo ionic interaction with basic compounds after dissociation.

These forces are secondary to non-polar interactions and therefore are referred to as secondary interactions. Secondary interactions are undesirable for reversed phase silica sorbents and can usually be eliminated by the End capping technique;