# Recent Advances in Applications of Ionic Liquids in Miniaturized Microextraction Techniques
## 2 Ionic Liquids in Miniaturized Microextraction Techniques  
### Solid-Phase Microextraction (SPME)  
Solid-phase microextraction (SPME) is a widely known sample preparation technique, combining sampling and pre-concentration, due to its quickness and cost-effectiveness with absence of organic solvents. Since its establishment by [PERSON] and co-workers it has been performed combined with several types of commercial sorbent coatings, such as polydimethylsiloxane (PDMS), polyacrylamide, carboxen, PDMS-carboxen or divinylbenzene (DVB) depending on the analyte [19; 20]. In a recent study of [PERSON] and [PERSON], a porous polymeric ionic liquid, poly(1-vinyl-3-(4-vinyl-benzyl)imidazolium chloride), was synthesized and used as a sorbent coating for SPME for the analysis of polar organic acids [21]. The results showed that the fiber was more sensitive and practical for the extraction of polar compounds in comparison with the commercial fibers. Ionic liquids compromise another effective type of sorbent coating that can be coupled with SPME technique in two different modes, headspace (HS-SPME) and direct immersion (DI-SPME). In the first mode, the sorbent coating is exposed to the headspace of the sample where the target analyte is present, while in the second the SPME-fiber is pushed out of the hollow needle and immersed into the sample directly. Following the sorption of the analyte in both cases, the fiber is drawn into the needle, the needle is withdrawn from the sample vial and transferred to the injection port of an analytical instrument, where desorption of the analyte takes place and the analysis is carried out [4; 22]. A benzyl-functionalized crosslinked polymeric ionic liquid (PIL) was developed by [PERSON] et al. and successfully used as a sorbent coating in headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography with flame-ionization detection for the determination of seven volatile polycyclic aromatic hydrocarbons (PAHs) in environmental water samples [23]. The VBHDIM-NTf\({}_{2}\) IL monomer and (DVBIM)\({}_{2}\)C\({}_{12}\)-2 NTf\({}_{2}\) IL cross-linker were used for the synthesis of the crosslinked PIL-based sorbent coating. Figure 3 represents the schematic illustration of HS-SPME procedure using the benzyl-PIL fiber for the extraction of PAHs. Compared to the commercial PDMS fiber coating for the PAHs, the crosslinked PIL fiber showed higher log K\({}_{\mathrm{fs}}\) due to the presence of benzyl moieties within the IL monomer and IL crosslinker of the PIL sorbent coating indicating its superior affinity, higher sensitivity with low LODs, ranged from 0.01 to 0.04 \(\upmu\)g L\({}^{-1}\) for the PIL-benzyl fiber and from 0.01 to 0.07 \(\upmu\)g L\({}^{-1}\) for the PDMS fiber. The linearity, the RSD values and the relative recovery values were more satisfactory for the PIL-benzyl fiber than the PDMS fiber. The presence of benzyl moieties  
Figure 2: Number of published scientific papers worldwide per year (from 2009 to 2018) on the applications of ionic liquids in sample preparation techniques (based on Scopus and ScienceDirect). in the PIL coating material enhances \(\pi\)-\(\pi\) interactions between the target compounds (PAHs), which are composed of aromatic rings, and the sorbent coating. In-tube SPME is an improved mode of SPME sample preparation technique introduced by [PERSON] in 1997, where the coupling of SPME with HPLC is achieved more conveniently. [PERSON] et al. developed a fiber-in-tube solid phase microextraction device with copper support modified via chemical bonding with ionic liquids. Especially, one copper tube was filled with eleven copper wires functionalized with ionic liquids and it was combined online with a high-performance liquid chromatography system to strengthen extraction capacity and eliminate dead volume, building an online in-tube SPME-HPLC system. In this framework, an in-tube SPME-HPLC method for the determination of estrogens in water samples was developed with high enrichment factors and satisfactory sensitivity (LODs: 0.02-0.05 g L\({}^{-1}\)).