## 4 Conclusions  
Thin-film microextraction blades coated with silica particles containing polar end-capping groups provided the best extraction efficacy out of all evaluated types of octadecyl-bonded particles. This type of coating is also characterized by the strongest correlations between the efficacy of the extraction process and hydrophobicity of the analytes, despite not having the highest density of hydrophobic octadecyl ligands. For example, while the hydrophobicity parameter (\(H\)) of Synerg\({}^{\text{\tiny{TM}}}\) Hydro-RP particles containing polar end-capping groups is higher than the \(H\) parameter of an average octadecyl particle (according to the hydrophobic-subtraction model [43; 44]), the \(H\) of these particles is lower than the \(H\) of NUCLEODUR\({}^{\circledR}\) C\({}_{18}\) Htec particles [44]. This was not reflected by the results of this study, where the less hydrophobic polar end-capped particles provided better extraction efficacy of the hydrophobic analytes. This suggests that the extraction of small molecules from aqueous samples with the conventional TMS end-capped octadecyl-bonded particles differs from the theoretical expectations. Moreover, in the hydrophobic-subtraction model, polar end-capping groups closely resemble TMS groups [45]; thus, this difference in end-capping type does not provide a satisfactory explanation for the correlations observed with the tested particles. Therefore, one may hypothesize that the extraction yields of TMS end-capped particles are below the theoretical optimal performance due to immersion in a water-based matrix, with which they are not compatible. Such a situation could not occur with water-compatible polar end-capped particles that retained their original characteristics throughout extraction. This reasoning seems to elucidate the benefits of using fully water-compatible stationary phases for extraction from aqueous samples, and was reflected by the results of this study. Additional investigation is required to assess whether water-compatible polar end-capping can improve extraction efficacy with ligands other than the octadecyl groups that were evaluated in this study. Some examples of stationary phases that are relatively popular in liquid chromatography and susceptible to so-called stationary phase collapse include octyl (C\({}_{8}\)) and phenyl-hexyl. These chemistries could significantly benefit from the incorporation of polar end-capping groups. However, if that were confirmed, then a significant breakthrough in solid phase microextraction could be achieved by preserving all original ligand traits, which may result in improved extraction efficacy. This process may then broaden the range of successfully used liquid chromatography-compatible coatings for future SPME devices and promote methods' use as a green alternative for sample preparation enabling low organic solvent consumption without compromising the extraction yield. The following are available online, Table S1. Coefficients of determination (R\({}^{2}\)) determined during calibration runs in different desorption solvents; Table S2. Number of results in each category for every stationary phase--desorption solvent combination; Table S3. Extraction efficacies [%] for each stationary phase--desorption solvent combination. ; Table S4. Essential physicochemical properties of the analysed substances. ; Table S5. List of reference standards in alphabetical order. ; Table S6. Monitored precursor--product ion(s) transitions. Conceptualization, L.S. ; methodology, L.S., D.K. and K.G. ; validation, L.S. ; formal analysis, L.S. and D.K. ; investigation, L.S. ; resources, K.G. ; data curation, L.S. and D.K. ; writing--original draft preparation, L.S. and D.K. ; writing--review and editing, L.S., D.K. and K.G. ; visualization, L.S. and D.K. ; supervision, L.S. and K.G. ; project administration, L.S., D.K. and K.G. ; funding acquisition, K.G. All authors contributed equally. All authors have read and agreed to the published version of the manuscript.