## 3 Application of MOFs as Sorbents in Selected Techniques of Preparing Liquid Samples for Analysis
### Matrix Solid-Phase Dispersion (MSPD)  
One of the lesser-known sample preparation techniques is a matrix solid-phase dispersion (MSPD). The first mention of this technique dates back to 1989, when [PERSON] et al. described using it to isolate drug residues from tissues [121]. The concept of the technique itself is quite simple. It is designed for the analysis of solid and semi-solid samples. The sample and sorbent material are blended (for example, in a mortar) and then transferred into an empty SPE column or a syringe tube. The mixture of sorbent and sample is placed between two frits and then compressed (using a syringe-plunger) to avoid the formation of channels or air bubbles in the sorbent (Figure 18). The subsequent sample preparation steps are very similar to the typical SPE procedure. This technique ensures that the sample is completely broken down and dispersed into tiny particles, providing a better surface area for the subsequent sample extraction [122]. The sorbent used additionally acts as an abrasive for the sample during blending. Generally, a good compromise between a large surface area, good dispersion, and improved contact with the solvent is provided with the sorbents with a particle size of 40-100 \(\upmu\)m. However, sorbents with a smaller particle size have also been used, although this leads to prolonged solvent elution times and possible blockage of the columns [123]. Since then, the technique itself has evolved considerably and increased the possibility of using both a range of classical [123] and modern nanomaterials, such as molecular-sieve-based sorbents, mesoporous materials, MOFs, molecularly imprinted polymers, and any others [124]. Due to the nature of this technique (the need to fill an empty column with a blended mixture of sample and sorbent), it is best suited for the analysis of solid, semi-solid, and viscous samples, such as biota, animal samples, and plants, but also sewage sludge and soil. MSPD is mainly used to analyze organic contaminants in environmental samples, for example, pesticides, herbicides, and fungicides in soil samples or pharmaceutical and cosmetic residues in plant samples [124; 125]. [PERSON] et al., in their review article, described these problems and the most common applications of the MSPD technique, which are similar to the examples mentioned above [126]. The authors addressed the basic issues of MSPD but did not pay special attention to the applicability of modern sorbents, where this was mentioned in only one subsection. Another review article on MSPD does not focus directly on the technique itself but rather on the various ways to determine pharmaceuticals and cosmetics in sewage sludge, where MSPD is only one of several options for sample preparation [127]. Another review paper, written by [PERSON] et al., once again focuses not on the MSPD technique itself but on its application to determining pesticides in fat-containing foods [128]. Having said that, the works mentioned may be a perfect choice for more target-oriented users. To the best of our knowledge, there is no review article or at least a more comprehensive mention of the possibility of using MOFs as sorbents in MSPD. The most commonly used sorbents in the MSPD technique are classical sorbents such as C\({}_{8}\), C\({}_{18}\), or silica. They are characterized by high mechanical strength and versatility. On the other hand, MOFs exhibit a large specific surface area, and there is a possibility of adjusting their structure to increase the selectivity of the analysis. These advantages of MOFs, combined with molecularly imprinted polymer, were used by [PERSON] et al. for the pyrethroids residue  
Figure 18: Application of the MSPD technique—variant [author’s own elaboration]. extraction from wheat [129]. The authors synthesized the sorbent used in the study and then characterized it using a series of instrumental techniques. The research methodology was successfully applied to detect residues of three pyrethroids in six wheat samples.