Preparation of a novel hollow-shaped carboxyl-functionalized microporous organic network for efficient solid-phase extraction of indoleamines from fruit juice samples.

Accurate quantification of indoleamines such as melatonin in complex food matrices is crucial for identifying rich dietary sources and developing potential adjuvant therapies. In this study, a novel hollow-structured, hydrophilic carboxyl-functionalized microporous organic network (H-MON-2COOH) was designed and synthesized via a sacrificial-template approach for the efficient solid-phase extraction (SPE) and determination of three typical indoleamines in fruit juice samples. The material exhibits a high surface area, excellent stability, and robust mechanical strength, along with abundant interaction sites enabling π-π stacking, hydrogen bonding, and electrostatic interactions for indoleamines. These properties collectively facilitate highly selective and sensitive analysis, demonstrated by wide linear ranges (0.9-1000 μg L-1), low limits of detection (0.3-0.8 μg L-1), high enhancement factors (94.7-96.2), satisfactory precision (RSDs < 6.5 %), excellent reusability (> 50 cycles), and outstanding chemical stability. The hollow architecture significantly improves mass transfer, leading to rapid adsorption equilibrium. Compared to commercial adsorbents including C18, activated carbon, and HLB, H-MON-2COOH showed superior extraction recovery. This study underscores the promising application of functionalized hollow MONs in sample pretreatment and food analysis.