Influence of Ligand Functionalization of UiO-66-Based Metal-Organic Frameworks When Used as Sorbents in Dispersive Solid-Phase Analytical Microextraction for Different Aqueous Organic Pollutants

Abstract

Four metal-organic frameworks (MOFs), specifically UiO-66, UiO-66-NH2, UiO-66-NO2, and MIL-53(Al), were synthesized, characterized, and used as sorbents in a dispersive micro-solid phase extraction (D-µSPE) method for the determination of nine pollutants of different nature, including drugs, phenols, polycyclic aromatic hydrocarbons, and personal care products in environmental waters. The D-µSPE method, using these MOFs as sorbents and in combination with high-performance liquid chromatography (HPLC) and diode-array detection (DAD), was optimized. The optimization study pointed out to UiO-66-NO2 as the best MOF to use in the multi-component determination. Furthermore, the utilization of isoreticular MOFs based on UiO-66 with the same topology but different functional groups, and MIL-53(Al) to compare with, allowed us for the first time to evaluate the influence of such functionalization of the ligand with regards to the efficiency of the D-µSPE-HPLC-DAD method. Optimum conditions included: 20 mg of UiO-66-NO2 MOF in 20 mL of the aqueous sample, 3 min of agitation by vortex and 5 min of centrifugation, followed by the use of only 500 µL of acetonitrile as desorption solvent (once the MOF containing analytes was separated), 5 min of vortex and 5 min of centrifugation. The validation of the D-µSPE-HPLC-DAD method showed limits of detection down to 1.5 ng·L−1, average relative recoveries of 107% for a spiked level of 1.50 µg·L−1, and inter-day precision values with relative standard deviations lower than 14%, for the group of pollutants considered.

Mixed Functionalization of Organic Ligands in UiO-66: A Tool to Design Metal–Organic Frameworks for Tailored Microextraction

“…A step forward in ensuring the true expansion of MOFs as competitive materials for D-µSPE requires not only the assurance of a better performance than that resulting from commercial materials (exhaustive comparison and inter-laboratory validation) [5,10], but also deep evaluation of the main factors of MOFs justifying the improved analytical performance for target compounds [11,12]. Gaining an understanding of the process can serve as the basis of proper MOF design.…”

“…Lirio et al also pointed out the influence of the metal, particularly the radius of the metal [13]. Taima-Mancera et al showed the positive effects of incorporating polar functionalities in the organic ligand of the MOFs used in D-µSPE when intending to extract polar analytes of a small size [12], with this idea having been further expanded by Boontongto et al to other application studies for polar analytes [14].…”

“…Among Zr-based MOFs, UiO-66(Zr) and UiO-66-type MOFs have been studied the most, given their superior chemical and hydrothermal stability, together with their simple (and mild) preparation [23] and green aspects [24]. Therefore, they have appeared as sorbents in a number of recent D-µSPE studies [12,25,26,27].…”

Metal-Organic Frameworks in Green Analytical Chemistry

“…If we take into consideration the idea of avoiding the use of heavy metals when designing MOFs, it is clear that many MOFs included in Table 2 present non-toxic metallic ionic centers [54,65], such as Zn 2+ [93], Zr 4+ [82] or Al 3+ [54]. Regarding the synthetic solvents in MOFs preparations, most studies employ DMF [82,90,94], avoiding in this way toxic chlorinated ones, such as dichloromethane or chloroform. Furthermore, the DMF volumes required are usually low (around 30 mL for 15 mg of MOF).…”

“…In general, quite low amounts of MOF as sorbents are always needed [54,82,84] in all microextraction procedures listed, from 2 mg [80] to 60 mg [89]. Regarding extraction times, there are reported values around 3 min or even less [85] for µ-dSPE and some of its applications in the magnetic variant [89,91].…”