Abstract:

Sulfonamide antibiotics（SAs） are artificially synthesized antibiotics， which have been widely used in the medical industry and animal husbandry because of their broad antibacterial property. Unfortunately， SAs can be metabolized by humans or animals and enter the environment through surface runoff， posing threats to environmental ecology and human health. Therefore， it is crucial to develop simple， rapid， highly efficient， and sensitive analytical methods for detecting SAs in water. Sample pretreatment is important for the extraction and enrichment of pollutants from environmental water. Magnetic solid-phase extraction（MSPE） is a new sample pretreatment method， which uses magnetic materials as adsorbents dispersed in solution， and rapid separation can be achieved by the aid of external magnets. Because of its advantages of short enrichment time， less organic solvent consumption， and easy separation of adsorbents， MSPE has attracted much attention. The key to MSPE is the preparation of highly selective magnetic adsorbents. Covalent organic frameworks（COFs） have the advantages of large surface， chemical and thermal stability， tunable porous structure， low density and easy functionalization. Therefore， a sample pretreatment method combining MSPE and COF for the analysis of SAs in complex matrices is very promising. The contents of SAs in environmental water are low， ultra performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS） has high sensitivity and accuracy. In this paper， the magnetic COF material Fe₃O₄@TpDT was prepared by in-situ synthesis method， which was used as an MSPE adsorbent for the adsorption and enrichment of eight SAs in environmental waters. Based on the π-π conjugation， hydrogen bonding， electrostatic interaction and molecular size effect between Fe₃O₄@TpDT and SAs， in combination with UPLC-MS/MS， this study established a new method for the determination of eight SAs in environmental water samples. The successful synthesis of Fe₃O₄@TpDT was confirmed using scanning electron microscopy（SEM）， Fourier transform infrared spectroscopy（FT-IR）， X-ray diffraction（XRD）， surface area analyzer and X-ray photoelectron spectroscopy（XPS） spectrum. To obtain the optimal extraction efficiency， the extraction conditions（dosage of material， pH of water sample， extraction time） and elution conditions（type and volume of elution solvent， elution time） were systematically investigated. The optimization results show that the Fe₃O₄@TpDT adsorbent can completely adsorb the target compounds within 6 min. After elution with 1 mL of methanol for 2 min， the target compounds can be fully desorbed. The target compound were separated on an ACQUITY UPLC BEH C18 column（100 mm×2.1 mm， 1.7 μm） and gradient elution was carried out with methanol-0.1% formic acid solution as the mobile phase. Multiple reaction monitoring（MRM） was conducted in the positive electrospray ionization mode and the ion source temperature and ion source voltage were set to 500 ℃ and 5 kV， respectively. Under the optimal extraction conditions， the enrichment factors（EFs） of Fe₃O₄@TpDT for eight SAs were 39‒48. The methodological verification results indicated that the eight SAs had good linear relationships（correlation coefficients（r²）≥0.992 6）， and the limits of detection（LODs） and quantification（LOQs） were 0.80‒3.44 ng/L and 2.66‒11.47 ng/L， respectively. The spiked recovery tests were conducted at three spiked levels（50， 500 and 800 ng/L） in blank water samples（tap water plant effluent）. The recoveries of the eight SAs were 73.0%‒112.9%， and the intra- and inter-day precisions were 4.4%‒12.5% and 8.7%‒19.2%， respectively. Finally， this method was successfully applied to the determination of eight SAs in environmental water samples（tap water plant effluent， reservoir water and seawater）. The results showed that no SAs were detected in tap water plant effluent， three SAs were detected in the reservoir water， and one SA was detected in the seawater. At three spiked levels（50， 500 and 800 ng/L）， the recoveries of eight SAs in reservoir water and seawater were 55.0%‒100.9%， and the relative standard deviations（RSDs） were 1.3%‒14.0%. This method is simple to operate， has a short extraction time， and has good accuracy and precision， providing technical support for the enrichment detection of SAs in environmental water samples.

Key words: covalent organic framework materials, magnetic solid-phase extraction（MSPE）, ultra performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）, sulfonamide antibiotics（SAs）, environmental water