# Recent Advances in Applications of Ionic Liquids in Miniaturized Microextraction Techniques
## 1 Introduction
The chemical and physical properties of ILs, such as polarity, hydrophobicity, viscosity, depend on the anionic and cationic constituents giving them the characterization, \"designer solvents\" [11; 12; 13; 14; 15]. Among the approximate 10\({}^{18}\) anion-cation combinations that can synthesize ionic liquids, there is a great majority of combinations that have toxic effects on water, environment, bacteria, plants, fish and human [16]. In a recent quantitative structure-property/activity relationship study of [PERSON] et al., a database for the toxicity of ILs has been established [17]. The authors conclude that the toxicity of ILs is related to the number of oxygen atoms that are present in the molecule. Also, the anion [NTf\({}_{2}\)]\({}^{-}\) influences the level of toxicity of ILs. However, the relationship of the toxicity and the length of the alkyl side chains is not always proportional. Therefore, it is crucial researchers get advice from relevant databases before synthesis and use of ILs either for industrial or laboratory use. Furthermore, there are guides not only for the selection of ionic liquids but for the solvents generally. One of the most useful tools for solvent selection has been proposed by scientists of Pfizer and it is presented in Table 1[18]. ILs are not always \"green\" solvents. Some of them are made from toxic ions and they are not biodegradable, despite their promiscuous physicochemical properties. Of course, not all the organic solvents that are used in the laboratories are toxic and harmful for the environment, but some of them can be replaced by other types of solvents with lower environmental impact. This review summarizes the recent advances in application of ionic liquids in miniaturized liquid and solid phase extraction techniques as extractants, intermediate solvents, mediators, and desorption solvents. As it is shown in Figure 2, the amount of published studies associated with ionic liquids has grown rapidly within the last decade. Some of the most important sample preparation techniques covered include solid-phase microextraction (SPME), dispersive liquid-liquid microextraction (DLLME), single-drop microextraction (SDME), stir bar sorptive extraction (SBSE), stir cake sorptive extraction (SCSE). Figure 1: Structures of common cations and anions of ionic liquids. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Preferred** & **Usable** & **Undesirable** \\ \hline Water & Cyclohexane & Pentane \\ Acetone Ethanol & Heptane & Hexane(s) \\
2-Propanol & Toluene & Di-isopropyl ether \\
1-Propanol & Methylcyclohexane & Diethyl ether \\ Ethyl acetate & Methyl t-butyl ether & Dichloromethane \\ Isopropyl acetate & Isooctane & Dichloroethane \\ Methanol & Acetonitrile & Chloroform \\ Methyl ethyl ketone & 2-MethylITHF & Dimethyl formamide \\
1-Butanol & Tetrahydrofuran & N-Methylpyrrolidone \\ t-Butanol & Xylenes & Pyridine \\ Ils (nontoxic combinations of ions) & Dimethyl sulfoxide & Dimethyl acetate \\  & Acetic acid & Dixoxane \\  & Ethylene glycol & Dimethoxyethane \\  & Benzene & \\  & Carbon tetrachloride & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Solvent selection guide.