Studies On The Application Of Magnetic Solid-phase Extraction In Analyzing Environmental Samples

In the tradditional environmental sample pretreatments, solid-phase extraction (SPE) is a most commonly used technique which can be employed to extract and clean-up analytes. However, SPE is relative laborious and time-consuming, since it requies the column-passing procedure, especially for large volume samples. Recently, magentic materials in analytical field have received increasing attention. Magnetic materials as adsorbents have several advantages in comparison with traditional non-magnetic adsorbents in the application of sample pretreatment. Firstly, the magnetic adsorbents still keep their unique adsorption characteristics. Secondly, the separation process can be performed directly in crude samples containing suspended solid material without additional centrifugation or filtration, which makes separation easier and faster.Magnetic solid-phase extraction (MSPE) as a new SPE technique, it combines the advantages of magnetic materials and tradditional SPE. MSPE can escape the time-consuming column-passing procedures, which has the advantages of high extraction yield, high concentration factor, short analysis time, low analysis cost and so on.In this study, the application of MSPE in the analysis of antibiotics residue in environmental samples was investigated. The main contents are as follows:1. Alumina-coated magnetite nanoparticles (Fe3O4 /Al2O3 NPs) were synthesized successfully throughout chemical coprecipitation method and alkoxide hydrolysis precipitation method. They were activated under 500℃and were applied to the analysis of sulfonamides (SAs) in different soil samples based on magnetic solid-phase extraction (MSPE). The extraction and concentration process was carried out in a single step by mixing the extraction solvent acetonitrile, magnetic adsorbents and soil sample under ultrasonic action. Then, the adsorbents were isolated from the complicated matrix easily with an external magnetic field. The SAs desorbed from the adsorbents were determined by liquid chromatography-tandem mass spectrometry. Compared with other methods reported in literatures, the extraction and clean-up steps could be fulfilled synchronously in the MSPE method and magnetic adsorbents can be completely isolated from matrix in a short amount of time (less than 1 min) by a strong magnet, which simplified the operation procedure and reduced the analysis time. Under the optimum conditions, the recoveries of SDZ, SMR, SMX, SMM, SMD and SDM by analyzing the five spiked soil samples were between 71% and 93% except for SQX (42%-60%). This may be due to the stronger hydrophobic property of SQX. Detection limits of SAs were between 0.37 and 6.74 ng g-1. It was also found that the"aging"effect of SAs contaminated soil could cause the recoveries to decrease. This reason may be due to the intense adsorption of soil or the degradation / transformation of the SAs。2. Alumina-coated magnetite nanoparticles (Fe3 O4 /Al2O3 NPs) modified by the surfactant sodium dodecyl sulfate (SDS) in acidic solution has been successfully synthesized and applied for extraction of trimethoprim (TMP) from environmental water samples based on mixed hemimicelles solid-phase extraction (MHSPE). The SDS-coated Fe3 O4 /Al 2 O3 NPs adsorbents were isolated under an adscititious field. The analyte of TMP desorbed was determined by liquid chromatography. Due to the high surface area of these new adsorbents and the excellent adsorption capacity after surface modification by SDS, satisfactory concentration factor of 1000 using this method to extract 500 mL of environmental water samples can be achieved with only 0.1 g Fe3 O4 /Al 2 O3 NPs and 80 mg SDS. This method was applied to some real environmental water samples and a certain amount of TMP was found in Hospital primary sewage effluent. The recoveries of TMP by analyzing spiked water samples were between 67% and 86%, and the relative standard deviation (RSD) ranged from 2 to 6%. Detection and quantification limits of the proposed method were 0.09 and 0.24μg L-1, respectively. Compared with conventional SPE methods, the advantages of this new Fe 3 O4 /Al 2 O3 NPs MHSPE method include easy preparation and regeneration of sorbents, short times of sample pretreatment, high extraction yields, easy elution, and high breakthrough volumes.3. The magnetic mixed hemimicelles solid-phase extraction (MMHSPE), based on the adsorption of cation surfactant octadecyltrimethylammonium bromide (OTMABr) onto magnetite nanoparticles (Fe3 O4 NPs) to form mixed hemimicelles, was proposed for the preconcentration of several sulfonamides (SAs) compounds including sulfamethoxazole (SMX), sulfamethoxydiazine (SMD), sulfadimethoxine (SDM) and sulfaquinoxaline (SQX) from environmental water samples. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of OTMABr-coated Fe3 O4 NPs with an adscititious magnet. SAs were eluted from OTMABr-coated Fe3 O4 NPs with 6 mL methanol assisted by ultrasonic. The elution was determined by liquid chromatography after concentration by N2. Mixed hemimicelles formed on the surface of Fe3 O4 NPs by OTMABr showed great adsorptive tendency towards analytes. The OTMABr-coated Fe 3 O4 NPs adsorbents were easy to be prepared, low cost and environmentally friendly. A concentration factor of 1000 was achieved by the extraction of 500 mL of environmental water samples using MMHSPE. Detection limits obtained for SMX, SMD, SDM and SQX were 0.026, 0.024, 0.033 and 0.030μg L-1, respectively. Good recoveries (70–102%) with low relative standard deviations (1–6%) were achieved in analyzing spiked water samples. Low concentration of SQX was found in hospital primary and final sewage effluent sample.The common ground among the three experiments is that they combine the advantages of magnetic materials and SPE/MHSPE. The magnetic adsorbents can adsorbe analytes without sacrificing their unique magnetization characteristics. The extraction and clean-up steps are gather in integral whole. The method simplifies operation procedures, reduces analysis time, improve determination sensitivities. Therefore, it will have great potential and application valve in analytical chemistry field.