**3.2 Liquid-Solid (L/S) ratio**

Another important parameter to consider in the set-up of a MASE protocol is the ratio between the amount of sample and the volume of solvent. The latter should be enough to cover the sample during the entire process, especially when the matrix swells during the extraction process. Although in conventional extraction higher is the volume of solvent, higher is the yield of the extract, in MASE larger volume of solvent may result in more energy and time to heat the suspension and in a lower yield due to a non-uniform distribution and exposure to microwave. Usually, an L/S from 10:1 to 20:1 (mL/mg) is found to be the right ratio in many extractive processes reported in the literature [20].

Strictly correlated to the L/S ratio is the stirring rate since it affects the mass transfer process in MASE. However, the significance of this parameter is rarely explored. By stirring, the mass transfer barrier created by the concentrated compounds in a localized region due to insufficient solvent can also be minimized resulting in better extraction yield. In other words, agitation accelerates the

extraction speed by accelerating the desorption and dissolution of compounds bound to the sample matrix [17].
