## 3 Application of MOFs as Sorbents in Selected Techniques of Preparing Liquid Samples for Analysis
### Dispersive Solid-Phase Extraction (D-SPE) and Micro-Solid-Phase Extraction (\(\mu\)-Spe)
Analyzing articles on the use of MOF in dispersion techniques for the preparation of liquid samples for chromatographic analysis, it is easy to observe the considerable popularity of MOFs, hiding under the acronym MIL--Materials from Institut Lavoisier, for example: MIL-125(Ti) [69], MIL-101(Cr) [70], MIL-100(Fe) [71], and MIL-53(Al) [72]. The second most commonly used MOF is UiO-66 [73] and UiO-67 [74]. Authors use those not only for water samples but also food products like meat [74], honey [71], oils [70], for synthetic urine [75], and human plasma [76]. The most commonly determined analytes are non-steroidal anti-inflammatory drugs [77], steroid hormones [78], mercury [76], herbicides [79], and progesterone [75]. The authors of this work [69] took an interesting approach to using MOF in the D-SPE technique. The authors used composite material as a disc, made by combining MIL-125(Ti) and In\({}_{2}\)S\({}_{3}\) (Figure 11). The compound with indium wasused to enhance the adsorption efficiency of aromatic analytes from water samples. The solvothermal method carried out both the synthesis of MIL-125(Ti) and binding it to the In\({}_{2}\)S\({}_{3}\). The material thus developed was used to determine sixteen selected nitro-polycyclic aromatic hydrocarbons in aqueous samples. The developed analytical method, combined with the GC-NCI-MS/MS technique, allowed the detection of the tested compounds with LOD at the level of 2.9 to 83.0 ng/L, with RSDs <10% and recoveries for individual analytes, ranging from 71.3 to 112.2%. To determine selected tetracyclines in honey samples using the D-SPE technique, can be used a mixture of three MOFs: MIL-101(Cr): MIL-100(Fe): MIL-53(Al) in a ratio of 7:1:2 (Figure 12) [71]. The MOF mixture was placed directly in diluted honey samples, the samples were subjected to shaking and ultrasound. The procedure combined with HPLC-MS/MS, allowed obtaining a limit of detection in the range of 0.073-0.435 ng/g, for up to four types of honey samples, with recoveries for analytes ranging from 88.1 to 126.2%. Progesterone is one of the hormones that plays an important role during pregnancy in mammals and in the growth and development of animals. Conventional analytical methods for the detection of this compound include GC-MS and HPLC-MS. The authors of this paper [75] presented an easy-to-perform procedure for determining progesterone in aqueous and synthetic urine samples using the D-\(\mu\)-SPE technique using MIL-101(Cr)-NH\({}_{2}\) as sorption material. Under optimized conditions, a wide linear range was obtained, from 0.5-500 ng/mL, with a relative standard deviation ranging from 2.4 to 8.4%. The recovery of the analyte ranged from 92.0 to 117.8% at three concentration levels (5, 25, and 100 ng/mL). These studies demonstrated an easy-to-apply approach to hormone analysis by combining the advantages of mass spectrometry and MOFs. In one of theworks [77], authors created a composite material--a cryogel for the first time by combining the MOF  
Figure 11: Synthetic protocol developed by [PERSON] et al. for the core-shell In\({}_{2}\)S\({}_{3}\)@MOF nanocomposite [69]. Figure 12: d-SPE procedure for the extraction of selected TCs (tetracyclines) from honey samples using MOFs as sorbents [71]. series with poly(vinyl alcohol, PVA). The MOF used are MIL-101(Cr), MIL-100(Fe), ZIF-8, MOF-199 and MIL-53(Al). The manufactured composite materials were combined with HPLC-MS/MS to detect four non-steroidal anti-inflammatory drugs in environmental water samples. The sorption properties of MIL-101(Cr)/PVA cryogel exceeded those of MIL-101(Cr) alone. Under optimal conditions, analytes were determined with LOD at the level of 0.007 to 0.037 \(\upmu\)g/L, and recoveries of the tested analytes ranged from 78.44 to 105.70% with a relative standard deviation ranging from 1.33 to 9.85%. The possibility of using MOFs as sorbents was investigated to determine the content of four selected androgens and progestogens in aqueous samples. MIL-101(Cr), MIL-100(Fe), MIL-53(Al.) and UiO-66 were used.