MOFs with 2,6-naphthalene dicarboxylic acid as organic ligand for solid phase microextraction of aldehyde biomarkers in the exhalation of lung cancer patients

In this work, four metal-organic frameworks (MOFs) including DUT-4, DUT-8, IRMOF-8, and MIL-140B were synthesized using 2,6-naphthalene dicarboxylic acid as organic ligand and Al³⁺, Co²⁺, Zn²⁺, and Zr⁴⁺as metal centers, then coated on stainless steel wires as solid-phase microextraction (SPME) fiber coatings. Five aldehyde biomarkers (hexanal, heptanal, octanal, decanal, and nonanal) in exhaled breath of lung cancer patients were used as the target analytes, and extracted using four MOFs fiber coatings, followed by thermal desorption and quantitative analysis using GC–MS. The DUT-4 was found to be the most appropriate sorbent. The developed SPME-GC–MS method has large enrichment factors (877–1711), wide linear ranges (0.5–1000 μg L⁻¹), and low detection limits (0.056–0.138 μg L⁻¹). The relative standard deviation for six replicate cycles using one DUT-4 coated fiber were 2.0–7.7 % (intra-day) and 2.2–4.6 % (inter-day), respectively. The fiber-to-fiber reproducibility for three parallel prepared fibers was in the range of 3.7–13.7 % (RSD). The fabricated DUT-4 coated fiber can withstand at least 100 cycles of extraction/desorption/conditioning without significant loss of extraction efficiency and precision. The high enrichment factors of the DUT-4 coatings are attributed to the high specific surface area, unique porous structure, and abundant aluminum coordinated unsaturated metal sites of the DUT-4 material. Moreover, the 2,6-naphthalene dicarboxylic acid has two benzene rings with a 180° orientation, which not only increases the hydrophobicity of the MOFs material to avoid water molecules occupying adsorption sites and helps to form a rigid skeleton structure with a large number of functional adsorption sites on the surface, thereby improving the enrichment factor of target analytes. Ultimately, the developed DUT-4 coated SPME fibers was sucessfully used for the analysis of exhaled breath samples, and the recoveries for the spiked analytes were in the range of 89–105 %.