## 2 Sample Extraction
### Dispersive Liquid-Liquid Microextraction  
In the last decade, the use of liquid-liquid extraction (LLE) has been limited as much as possible due to its increased environmental impact compared to SPE and SPME [88]. However, these last-mentioned techniques require dedicated tools and, in some cases, involve a pre-treatment step. Because of that, and for all those applications where LLE is the best sample preparation or cannot be replaced, this technique evolved towards the miniaturization and minimization of volumes. The best-in-class alternative to LLE was proposed in 2006 and is dispersive liquid-liquid microextraction (DLLME) [89]. In this protocol, a few mL of sample are treated using a reduced amount of organic non-polar extracting solvent and assisted by a higher volume of organic polar dispersive solvent. The extracting solvent is dispersed in small droplets into the sample using mechanical action or ultra-sound (UA-DLLME) to maximize area/volume ratio and mass transfer. In this step, the role of the dispersive solvent, together with the ethanol present in the matrix, is crucial to allowing analytes to move from the aqueous phase into the organic phase. Another relevant advantage of DLLME is its concentration factor, which enhances method performance.  
A further improvement, vortex-assisted LLME (VALLME), was published in 2010 [90]. It requires only basic laboratory equipment and is cost-effective in terms of time and economy [91]. The sample and the organic phase are mixed into an emulsion by vortexing. Because the solvent phase is broken into small droplets, the interfacial area is increased significantly. Based on this, the efficiency of mass transfer increases while the interfacial transfer coefficient remains constant [92]. In the final step of VALLME sample preparation, the emulsion is destabilized by centrifugation using high gravitational acceleration to obtain the separated organic and aqueous phases [93]. Because it involves the dispersion and aggregation of the extractant, its miscibility with the sample phase, and the mass transfer of the analyte between the phases, more investigations are still required to clearly describe the mechanism of this process. Due to this lack of mechanistic understanding, sample preparation parameters should be empirically defined. However, the final state of this in-solution sampling is a simple equilibrium, two-phase system. The concentration of an analyte in the sorbent phase only depends on the volume of the two phases and the distribution coefficient. VALLME has been successfully applied to the VOC analysis of beer and wine. However, basic knowledge of these processes is still lacking, limiting their application. In recent years, other forms of DLLME have progressed. Air-assisted liquid-liquid microextraction (AALLME) using a syringe for sucking and injecting the mixture of the organic phase the and aqueous sample does not require the assistance of dispersant solvents and therefore consumes fewer organic extractants [94]. Switchable hydrophilic solvents expand our understanding of liquid-liquid extraction [95]. It is named switchable polar solvent (SPS) or switchable hydrophilic solvent (SHS) and is controlled by carbon dioxide (CO\({}_{2}\)). The solvent can adjust the polarity, selectively extracting polar and non-polar substances. All these methods belonging to DLLME are becoming increasingly popular, and new developments, applications, and improvements are expected in the future.