| Dopamine (DA) is a well known neurotransmitter in the central nervous system, which affects a wide range of behaviors and functions, including cognition, motor activity, emotion, memory, neuroendocrine regulation, and selective attention. The quantification of DA in biological samples occupies an important position in clinical diagnosis and pathological mechanism research of neuropsychiatric diseases. Due to the low concentration level of DA existing in complicated biological sample, the separation and detection of trace DA have been an important issue.Stir bar sorptive extraction (SBSE) is a novel sample pretreatment technique which has been quickly developed in recent years. It possesses higher extraction capacity and self-stirring characteristic which can avoid competitive adsorption from additional stirrer. However, SBSE is suffering restriction for further development and applyment due to the limited types of commercial available coatings of stir bar. Molecularly imprinted stir bar sorptive extraction (MI-SBSE) combines the advantages of molecularly imprinted polymer (MIP) and those of SBSE, which can improve the selectivity and recognition of stir bar for the target. So, the stir bar coated with MIP can eliminate the interruptions of complex matrix in biological samples and has great development prospects.In this study, the stir bars coated with molecularly imprinted polymer (MIP-SBs) were prepared for the separation and detection of trace DA in human urine. The process of the study was described as follows.1. Preparation of MIP-SBsThe polymerization reaction was carried out by mixing189mg of DA,0.34mL of MAA,1.95mL of EGDMA,0.05mL of TRIM,35mg of AIBN,2.8ml of methanol and0.7mL of water in60for24h, the experiment conditions such as selection of solution, functional monomer, cross-linker and the amounts and ratio of reactants were optimized.And the conditions of extraction and desorption such as solvent, time, pH were also investigated. Then, the scanning electron microscopic image and Fourier transform infrared spectra of the coatings confirmed that the preparation of MIP-SBs was successful.2. Investigation on the performance of MIP-SBThe performance of MIP-SBs includes the extraction capacity, selectivity, solvent tolerance and durability. The adsorption capacities were calculated to be20.29nmol and5.06nmol for MIP-SB and non-imprinted polymer stir bar (NIP-SB), respectively. The adsorption capacity of MIP-SB was about4times over that of NIP-SB. The MIP-SBs showed better selectivity than NIP-SBs when used to extract DA from the mixture of DA and its three analogues. The recovery of DA with MIP-SBs was higher than its three analogues. Besides, the coatings of MIP-SBs in several organic solvents remained good surface quality.3. The application of MIP-SBsAn analytical method to determine DA in urine sample was established by combining MI-SBSE with HPLC-fluorescence detector. The linear range of dopamine concentration was0.378-18.9ng/mL with correlation coefficient of0.9995, and the limit of detection was about0.0189ng/mL (S/N=3), the limit of quantification was about0.0945ng/mL (S/N=10). The intra-day and inter-day relative standard deviations (RSDs) of the method were in a range of3.42%to8.61%, and all the recoveries of DA were higher than80%.The method built was applied to analyze DA in human urine. The amounts of DA in two healthy volunteers were1.19and1.07ng/mL, respectively. The recoveries of dopamine in spiked urine samples at three different levels were in a range of92.3%to106.8%, and the RSDs were all within13.2%(n=3).
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