## 1 Introduction  
Plants synthesize and secrete many different volatile organic compounds (VOCs). Biologically active substances that are produced by plants are phytochemicals; however, they are not ubiquitous and are the product of specialized metabolism, narrowed down to specific families and species of plants. A feature that distinguishes plant material is the wealth of compounds that are very diverse in terms of physicochemical properties that occur in a very wide range of concentrations. The sample preparation step is important for the reliability of the results of the determined compounds. The extraction of biologically active compounds depends on many factors, including extraction methods, the type of raw material, and extraction solvent. The selectivity of extraction, the number of analytes in the sample, and the ecological aspects are also of key importance [1]. Specialized metabolites may have a wide variety of polarities, solubility, volatility, thermal stability, and the presence of different functional groups. They are often found in low concentrations in the raw material; therefore, there is no universal and simple method to isolate them. Obtaining VOCs is a difficult process, as they make up a small fraction of the plant's raw material. Various extraction methods are used. The most common method of extracting essential oil from a plant is hydrodistillation (HD). Most often, it is carried out with a glass apparatus of the Clevenger or Deryng type. Both devices are recommended pharmacopoeia devices for determining the content of essential oils. The first is described by the _European Pharmacopoeia_ (VI) and the latter according to the _Polish Pharmacopoeia_ (VII) [2]. The efficiency of HD is a fairly complex issue. The general disadvantage of distillation methods is that it is difficult to quantitatively determine the essential oil of small amounts of plants, as the yields are typically low [3]. In the publications that have appeared thus far, various methods of extracting VOCs present in liverworts have been used [4; 5; 6]. The most common extraction methods for liverworts were headspace solid-phase microextraction (HS-SPME) and solid-liquid extraction (SLE) with solvents of different polarities [6]. In this study, SLE was performed with the use of three different solvents: n-hexane, diethyl ether, and methylene chloride. A Likens-Nickerson distillation was also performed for the extraction of VOCs, in which n-pentane was used to collect the extract. Another method of VOC extraction used was HD in a Clevenger apparatus. In this method, n-hexane was used to collect an extract. High temperature, exposure to air, and hot water or hot steam during long distillation times break down many of the unstable aromatic terpenoids. Due to the small plant samples that can usually be collected, these methods are not used very often. Therefore, comparing the ingredients obtained by the HD process as well as those from solvent extracts is essential to recognize whether they are natural products or compounds formed during the extraction [6]. The percentage of essential oil in the plant substance is often not high, which requires additional work to increase it or select other extraction methods, for example, microwave-assisted extraction (MAE) [7]. HS-SPME [5; 7; 8; 9; 10; 11; 12] and conventional methods, such as SLE, can also be used to extract VOCs [9; 10; 11]. Modern extraction methods are certainly more efficient and environmentally friendly as very little or no solvents are used [13; 14; 15]. Polar solvents, such as methanol, ethanol, or ethyl acetate, are used to extract hydrophilic compounds. For the extraction of more lipophilic compounds, dichloromethane or a 1:1 mixture of dichloromethane/methanol is used. In some cases, hexane extraction is used to remove chlorophyll [16; 17]. Appropriate extraction measures must be taken to ensure that potentially specialized metabolites are not lost, distorted, or destroyed during the preparation of a plant sample extract [16; 18].