# Recent Advances in Applications of Ionic Liquids in Miniaturized Microextraction Techniques
## 2 Ionic Liquids in Miniaturized Microextraction Techniques
### Single-Drop Microextraction (SDME)  
Single-drop microextraction technique (SDME) was first introduced by [PERSON] and [PERSON] in 1995 as an alternative extraction process eliminating the problems of solvent evaporation, which exists in LLE and SPE, and the degradation of SPME fiber [36]. The basis of this technique is the distribution of the target compounds and a microdrop of solvent that is suspended in the tip of a microsyringe needle. It uses small volumes of organic solvents and simple equipment reducing the total cost of each individual application. SDME can be performed with direct immersion (DI-SDME) in the aqueous sample or in the headspace of the sample (HS-SDME). The main limitation of this technique is the fact that the stability of droplet is highly depended on the used solvent. Thus, solvents with low viscosity, high vapor pressure and low surface tension decrease the effectiveness of the extraction process. ILs could be used as an alternative to the common organic solvents used in SDME.  
[PERSON] et al. used the SDME technique for the extraction and concentration of flavor and fragrance substances in fruit juices [37]. A hydrophilic IL, 1-hexyl-3-methylimidazolium tetrafluoroborate, used successfully as an extraction solvent. The method was validated after the optimization of the main parameters, such as the volume of solvent microdrop, the extraction time, the enrichment time, the temperature, the pH of the sample solution, the height of the microdrop above the solution surface. The method demonstrates satisfactory sensitivity and accuracy with relative standard deviations lower than 9.1%.  
A headspace single-drop microextraction (HS-SDME) method for the determination of aromatic analytes by HPLC was developed by [PERSON] et al. using as solvents tetrachloromanganate ([MnCl\({}_{4}\)\({}^{2}\)-])-based magnetic ionic liquids [38]. A rod magnet was used to sustain the microdroplet of MIL during HS-SDME. High stability of the microdroplet under high temperature and long extraction times was achieved due to the magnetic susceptibility of the MILs. The method showed high sensitivity and precision for the target compounds, and satisfactory relative recoveries from an application in real sample.  
He and co-workers developed an ionic liquid-based headspace single drop microextraction combined with high-performance liquid chromatography (HS-SDME-HPLC) method for the determination of camphor and trans-anethole in licorice tablets [39]. The ionic liquid used as the extracting medium was 1-bityl-3-methylimidazole hexafluorophosphate. The method showed satisfactory stability and sensitivity after setting the volume of the IL microdrop to 12 \(\upmu\)L. The method is simple, rapid, selective, precise, accurate and linear for the target compounds. SDME technique has the advantage that allows the single step separation, purification and enrichment improving the signal-to-noise ratio and ensuring the accuracy of the method as there was no loss of volatile components. The method is expected to be widely performed for the preparation of volatile compounds of drugs with high boiling points.