Water stable metal-organic framework packed microcolumn for online sorptive extraction and direct analysis of naproxen and its metabolite from urine sample

The metal-organic framework MIL-101 was fabricated in a polyetheretherketone (PEEK) tube as micro-trapping device, and applied to sorptive extraction of naproxen and its metabolite in urine samples. The remarkable water stability of the MIL-101 characterizes the material as being different from other moisture sensitive metal-organic framework. It is therefore suitable for extraction of pharmaceuticals from biological fluids. The adsorption isotherms in aqueous solution showed that the adsorption of naproxen on MIL-101 is endothermic. Additionally, MIL-101 exhibited higher extraction capacity to naproxen than that of C18-bonded silica and multi-walled nanotube. A specially designed in-tube sorptive extraction (ITSE) device endows the extraction process with the characteristic of rapidness, convenience, and easy of conjunction with high performance liquid chromatography (HPLC). Finally the MIL-101 based ITSE method coupled with HPLC and fluorescence detection was applied to analysis of naproxen and 6-O-desmethylnaproxen in urine samples. Parameters that influence the online extraction procedure, including pH of the sample solution, flow rate of extraction, sample volume, desorption solvents and time were investigated. The method is proved to be highly sensitive with the linear range of 0.05–6.0 μg L−1 and the limits of detection of 0.034 and 0.011 μg L−1 for naproxen and 6-O-desmethylnaproxen, respectively. The recoveries in urine samples were 85.3–98.3% for naproxen and 94.0–97.3% for 6-O-desmethylnaproxen with intra- and inter-day RSDs of 2.7–5.2% and 7.1–8.1%, respectively. Urine samples could be directly subjected to analysis without any additional sample pretreatment. The proposed method was demonstrated an efficient, flexible and versatile extraction tool which is ideally suitable for online conjunction with chromatographic methods.