Effective extraction of trace cytokinins in plants based on a carboxyl functionalized microporous organic network

Cytokinin (CK) is a type of hormone that exists widely in plants and plays a significant role in promoting cell proliferation and division. Developing a rapid and sensitive method for the detection of trace CKs remains challenging. Microporous organic networks (MONs) are novel materials widely used in sample preparation owing to their excellent extraction performance. Therefore, a dispersive solid phase extraction method based on carboxylated microporous organic networks (MON-2COOH), combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the detection of four CKs was developed. Upon introducing a carboxyl group into pure MON, the MON-2COOH material had excellent stability, high porosity, and a good dispersion effect, and provided more interaction sites to achieve good adsorption of target compounds. Under the best conditions, the established dSPE-UPLC-MS/MS method had the advantages of low adsorbent dosage (2 mg), low detection limit (1.0-10.0 pg mL^-1) and good reproducibility (RSD ≤ 6.54%, n = 5). Synergistic extraction mechanisms involving π-π, hydrogen bonding and hydrophobic interactions were elucidated using both density functional theory calculations and experimental data. This work also confirmed the feasibility of functionalized MONs as satisfactory adsorbents for the enrichment of small organic compounds.