Application Of Graphene And Fe₃O₄ Mixed Hemimicelles Solid-phase Extraction In Sample Preparation

Sample pretreatment is the key step in the process of sample analysis, so choosing the appropriate pretreatment method can improve the sensitivity and reduce the matrix effect, thus obtaining more accurate results. Due to its low cost and high extraction efficiency, solid-phase extraction is a kind of widely used sample pretreatment method, especially when dealing with liquid sample, the extraction and purification can be simultaneously performed, without phase separation steps.Traditional solid-phase extraction is poorly selective and time-consuming, which needs a lot of harmful organic solvent. This experiment will combine emerging nanomaterials with solid phase extraction, aiming to establish a kind of simple, fast and environmentally friendly sample pretreatment method. This thesis is divided into three parts and the main conclusions and original aspects are listed as follows :Chapter 1: This chapter simply summarized some commonly used sample pretreatment methods and introduced several emerging nanomaterials adsorbents and their application in solid phase extraction in recent years. The main thought and design idea are presented.Chapter 2: Lab-synthesized graphene as sorbent material was packed into a 1000 μL pipette tip for the extraction of five carbamate pesticides（pirimicarb, baygon, isoprocarb,baycarb and diethofencarb） in juice samples, combined with ultra performance liquid chromatography-tandem mass spectrometry for the rapid determination. The whole process of miniaturized graphene-based pipette tip solid phase extraction was finished in 8 minutes, the amount of sorbents was just 4 mg and the volume of eluent was 1.5 m L. The experimental parameters which may affect the results were optimized. Under the optimized conditions,good linear relationship（R2>0.999） and lower limits of detection（0.0022-0.033 ng/m L） were achieved. The relative standard deviation（RSD） of the reproducibility experiment was below4.12 %. The recoveries at three spiking levels ranged from 80.9 % to 124.6 %. Compared with other adsorbents including PRS, GCB, and C18, graphene with good extraction efficiencies of five carbamates was superior to other sorbents. The proposed method is simple, fast, less toxic,and highly selective.Chapter 3: Under the alkaline condition, lab-produced mesoporous Fe₃O₄ nanoparticles adsorbed cetyltrimethylammonium bromide（CTAB） to form mixed hemimicelles solid phase extraction system. Then the system was used to extract bisphenol A（BPA） and diethylstilbestrol（DES） from bulky bottled mineral water and combined with high performance liquid chromatography for the determination of the analytes. The experiment went like this: 50 mg magnetic nanomaterials dispersed into 250 m L water sample for 2minutes to achieve the maximum adsorption, then separated with an Nd–Fe–B strong magnet,and finally eluted with 1 m L methanol（containing 1 % acetic acid）. The eluant can be directly injected into liquid chromatography for analysis. All the extraction process was finished in 10 minutes. Main factors including the amount of CTAB, p H, extraction time and desorption conditions were optimized. Under selected conditions, the relative standard deviation（RSD）of the reproducibility experiment was below 4.28 %, the recoveries ranged from 80.90 % to124.60 %, and the enrichment factors of BPA and DES were 251 and 207, respectively. The proposed method is time-saving, environmentally friendly and suitable for the extraction of bulky sample. Moreover, to the best of our knowledge, it’s the first time to use magnetic mixed hemimicelles solid phase extraction for the extraction of DES.