Abstract:

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a class of synthetic drugs that do not contain glucocorticoids. NSAIDs are widely used for their analgesic, antipyretic, and anti-inflammatory effects. Due to their low adsorption coefficients and recalcitrance to biodegradation, NSAIDs readily enter environmental water through sewage discharge and exist stably for long periods. The long-term presence of trace amounts of NSAIDs in environmental water has adverse health effects on humans and animals. Therefore, it is important to establish an appropriately sensitive and reliable method for the determination of NSAIDs in environmental water, where their concentrations are low. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is highly selective and sensitive, and so is especially suitable for detection of NSAIDs. Solid phase extraction is one of the most commonly used pretreatment methods. The extraction efficiency depends mainly on the adsorbents used. Metal-organic framework (MOF) aerogel SPE materials combine the attributes of highly selective adsorption property and high affinity. Moreover, the monolithic structure of the MOF aerogel composite simplifies the solid-liquid separation process. In this work, a novel MOF/chitosan (CS) composite designated Co-UiO-67(bpy)/CS, was prepared as the adsorbent material to enrich ketoprofen (KPF), naproxen (NPX), flurbiprofen (FPN), diclofenac (DCF), and ibuprofen (IBF) in water. This facilitated the detection of these compounds by UPLC-MS/MS. Co-UiO-67(bpy) was synthesized by a solvothermal method by mixing zirconium chloride, cobalt chloride, and the organic ligand 2,2-bipyridine-5,5 dicarboxylic acid. A CS suspension was used to prepared the hydrogel, which was freeze-dried to obtain the Co-UiO-67(bpy)/CS aerogel. The prepared material was characterized by Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Co-UiO-67 (bpy) was embedded into chitosan. A layered porous MOF composite aerogel was observed. The extraction efficiency of the five NSAIDs was investigated and optimized by assessing type of extraction material, MOF amount, extraction time, sample pH, ionic strength, formic acid concentration in eluent, elution time, and elution volume. The optimized results showed that the target compounds could be completely adsorbed within 5 min. In the UPLC-MS/MS experiment, NSAIDs were analyzed in the negative ionization multiple radiation monitoring (MRM) mode. Gradient elution was carried out with 0.01% formic acid aqueous solution and methanol as the mobile phases. The analytical method was established in the optimized extraction conditions. The five NSAIDs displayed good linearity with linear correlation coefficients greater than 0.9937. The limits of detection (LODs) and limits of quantification (LOQs) of this developed method were 0.32-2.06 ng/L and 1.05-6.78 ng/L, respectively. Satisfactory recoveries of the five analytes were achieved within 74.5%-114.1% at three spiked concentrations of 40, 250, and 1500 ng/L, as well as good precision with relative standard deviations of 1.3%-12.3% (intra-day) and 1.3%-11.5% (inter-day). The method was then used to test real-world water samples. Trace amounts of ketoprofen and flurbiprofen were detected in municipal wastewater (14.52 ng/L and 10.05 ng/L, respectively). The method exhibited good sensitivity, accuracy, and precision, and the operation process was convenient. The present study thus presents a novel method for the detection of the trace NSAIDs in environmental waters.

Key words: ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), dispersive solid phase extraction (DSPE), metal-organic frameworks (MOFs), composite aerogel, nonsteroidal anti-inflammatory drugs (NSAIDs), environmental waters