2.3.5 Effect of Stirring
The effect of stirring is directly related to the mass transfer process in the solvent phase, which induces convection in the headspace. Therefore, equilibrium between the aqueous and vapor phases can be achieved more rapidly. The use of agitation in MAE accelerates the extraction by enhancing desorption and dissolution of active compounds bound to the sample matrix [ 50 ] . Through stirring, the drawbacks of the use of low solvent-to-solid ratio (S/F) can be minimized, together with the minimization of the mass transfer barrier created by the concentrated solute in a localized region resulting from insuf fi cient solvent [ 28 ] . In the work by Kovács et al. [ 51 ] it is possible to observe the difference between suspensions with and without stirring. The authors found that when the suspensions were agitated with magnetic stirrers the temperature reached its maximum value within a shorter time, and the temperature differences inside individual vessels were not signi fi cant.