## 5 Conclusions  
Many MOF materials are relatively unstable in an aqueous environment where they are hydrolyzed and subsequently degraded. The stability of MOFs in contact with water depends on many factors, one of which is the strength of the coordination bond connecting the organic ligand and the metallic node, while another is the steric obstacle that the ligand may pose to prevent water molecules from coming into contact with the reactive node. Currently, there are already several MOFs that show an increased resistance to water, and their sorption properties allow them to be used in various techniques for sample preparation for analysis. Among them, we can mention those belonging to the \"families\" ZIF--Zeolitic Imidazole Framework, Ui--University of Oslo, and MIL--Materials from Institut Lavoisier. These MOFs, due to their properties, are most often used by many researchers in their studies. One of the advantages of MOFs is the possibility of modifying them in a wide range, adapting their sorption properties to a specific application, and increasing sorption efficiency. Theoretically, it is possible to synthesize many types of MOFs, differing in the kind of ions or clusters of metals and organic connectors. In practice, only a few dozen MOFs are used. This is due to the difficulties encountered in the process of their synthesis or their price. Not every planned structure of MOF is possible to implement in practice, and the process of their synthesis itself depends on many factors, such as the type of solvent, type of substrates, concentration of substrates, presence of organic bases, type of counterions, temperature, mixing rate, etc. Because of these difficulties, in laboratory practice, few researchers deal with the matching of MOFs, either through directed synthesis or through the modification of the existing structure, in order to improve the sorption properties and to produce the sorbent thus obtained to a specific compound or group of compounds. The observed direction of development of these studies is usually based on the simple use of already available MOFs to investigate their general sorption properties (common organic pollutants present in the environment and possible modification of the sample preparation process for analysis). Although the modification of the structure of the MOF itself is an unpopular direction of work on their development, there is a clear tendency to create composite materials combining the advantages of MOFs with the advantages of other materials. The ingenuity of researchers in creating such composite materials is extremely high: cellulose aerogels, nanofibers, cotton, composites of the Fe3O4/TEOS/APTES type, graphene oxide, chitosan, and porous carbons. Often, the composite material created is aimed at adapting the material to be used in a specific sample preparation technique (MOF@Fe3O4 in MSPE). Varioustechniques are used to create new composite materials containing MOFs, giving the obtained materials a unique structure and properties, to eliminate the disadvantages of a given sample preparation technique, such as the use of electrospinning to get MOFs deposited on nanofibers, which eliminates the problem of high back pressure in the PT-SPE technique. Combining MOFs with another material could also positively affect their durability in the aquatic environment. Analyzing emerging scientific publications, it can be seen that another trend in using MOFs as sorbents for the analysis of liquid samples is the miniaturization and development of techniques such as D-SPE, \(\mu\)-SPE, MSPE, and PT-SPE. Due to the properties and high specific surface area of MOFs, it is possible to use these materials in micro-quantities without losses on the recovery and detection limit of the determined compounds. The use of smaller amounts of organic solvents and smaller amounts of sorbents translates into more significant savings for a given laboratory and is in line with the principles of green chemistry.