## 3 Analytical Procedures Using Microextraction Techniques for the Liquid Phase  
Classical liquid-liquid extraction (LLE) is one of the oldest techniques of enrichment and isolation in analytical chemistry and is still used in numerous analytical procedures [4]. However, while using the tedious and time-consuming LLE technique, large quantities of expensive and dangerous organic solvents are used. As a result, the latest research trends include miniaturisation of the traditional liquid-liquid extraction system, which is mostly aimed at decreasing the volumetric ratio of the acceptor-to-donor phase. Table 1 presents information on the stages of development and improvement of the microextraction technique to the liquid phase. At present, the LPME technique is used both for removing interferets, enriching analytes present in samples, and for the simplification of the composition of their matrix. The method of classification of various approaches in liquid-phase microextraction is presented in Figure 2.  
Figure 1: Diagram depicting the course of various procedures for determining organomercury and organotin compounds using microextraction techniques at the stage of preparing samples for analysis. Based on [PERSON] _et al_. [5]. Liquid-phase microextraction, in which the extraction solvent has the form of one drop, is called single-drop microextraction. In this technique, the use of an organic solvent is minimised to one drop (1-8 \(\upmu\)L), which makes it exceptionally environmentally friendly [7; 8; 9]. The SDME method can be used for liquid and gaseous samples. This method is an appropriate strategy for enriching the matrix composition before detection and is regarded as the basic LLME technique, which is successfully used for the extraction of organomercury and organotin compounds, e.g., from water samples [10; 11]. A single solvent or a mixture of solvents can be used for extraction to obtain higher selectivity. For metal ion extraction, chelating reagents dissolved in an organic solvent are used [12]. \begin{table}
\begin{tabular}{|l|l|} \hline
**Year** & **Methodological Solution** \\ \hline
**1995** & First single-drop-based extraction systems \\ \hline
**1996** & First drop-in-drop system \\ \hline
**1997** & Liquid stage microextraction in a dynamic system \\  & The use of microsyringe for supporting the drop \\ \hline
**1999** & Liquid-phase microextraction using fibre (LPME) \\ \hline
**2001** & Headspace Solid-Phase Microextraction (HS-SDME) \\ \hline
**2003** & Using ionic liquids as the extracting agent \\ \hline
**2005** & Using water as a solvent in liquid-phase microextraction \\ \hline
**2006** & Liquid-phase microextraction using ultrasound as a factor supporting the extraction process \\ \hline
**2007** & Liquid-phase microextraction using microwave radiation as a factor supporting the extraction process \\  & Automation of the single-drop microextraction process \\ \hline
**2008** & Combining microextraction to the liquid phase with flame atomic absorption spectroscopy \\ \hline
**2009** & Liquid-phase microextraction using an ionic liquid combined with dispensing a sample to the \\  & column using a thermal desorption device \\ \hline \end{tabular}
\end{table} 
Table 1: Stages of the development and improvement of the LPME technique [6]. Figure 2: Classification of various approaches in liquid-phase microextraction. In the case of the SDME technique, it is the ability to keep a solvent drop at the end of the needle, which is immersed in the analysed sample (DI) or is placed on the headspace phase of the sample (HS). Figure 3 presents this solution in the form of a diagram. Xenobiotics are divided between the sample and the organic phase based on passive diffusion [13,14]. In the case of the DI-SDME techniques, two liquid phases are in direct contact between each other, and the transfer of analytes from the water solution to the extraction drop lasts until thermodynamic balance is achieved or the extraction is stopped [11].