Spherical cellulose/chitosan aerogel–supported MOF-199 for the magnetic solid-phase extraction of benzodiazepines from urine

Metal–organic frameworks (MOFs) are promising materials for sample pretreatment. The performance improvement of powdered MOFs is hindered by their aggregation and difficult recovery. To overcome these issues, a biodegradable lightweight spherical aerogel was used as a support for the in situ growth of copper-based MOFs (MOF-199). Furthermore, Fe₃O₄ nanoparticles were incorporated into the aerogel to achieve magnetic properties. Thus, hybrid aerogel spheres containing MOF-199 supported on magnetic oxidized cellulose nanofiber/carboxymethyl chitosan (MOF-199@mag-CNF/CMC) were fabricated. The effects of Fe₃O₄ loading amount and organic-ligand concentration on the properties (spherical geometry and mechanical strength) of the hybrid aerogel spheres were studied. Their potential application in the extraction of benzodiazepines (BZPs) from urine samples prior to liquid chromatography–mass spectrometry was evaluated. The highly dispersed MOF-199 crystals on the spherical aerogel effectively overcame the inherent structural shrinkage of the bare aerogel spheres; thus, the MOF-199@mag-CNF/CMC aerogel spheres were robust and could withstand repeated use for at least eight consecutive extraction cycles. Further, MOF-199@mag-CNF/CMC exhibited improved BZP extraction efficiency, which was 2.5–11.6 times higher than that of bare Cu²⁺@mag-CNF/CMC aerogel spheres, primarily due to additional π–π interaction and H-bonding as well as improved specific surface area. Parameters influencing the extraction and desorption processes were also comprehensively investigated. Under optimal conditions, this method provided a wide linear range of 0.1–10 µg/L (R² > 0.995) and good precision (2.8–6.7% for intra-day; 1.9–7.8 % for inter-day). The limits of detection and quantification ranged from 0.02 to 0.11 µg/L and from 0.06 to 0.33 µg/L, respectively. The recoveries for the urine samples spiked with three concentrations of BZPs ranged from 73.9 % to 114.1 %. The proposed method is simple, sensitive and eco-friendly and can be used for the determination of BZPs from urine for clinical and forensic examinations.