| Sample preparation is one of the most important and crucial steps in analyticalprocess for the determination of some contaminants in food samples. It is not only toisolate the target compounds from the samples, thus reducing or eliminating theinterferences originally present in the sample, but also simultaneously to concentrate theanalytes to facilitate their determinations at low levels. Since conventional extractiontechniques are laborious and time-consuming. Therefore, it is necessary to develope somenew sample preparation techniques, which are simple, rapid, effective, and low pollution.Magnetic solid phase extraction and micro-solid phase extraction methods have undergonea rapid development and applications prospect in environmental, food and biologicalaspects. Graphene (G) has been widely applied in many fields due to its uniquecharacterisics such as large surface area, good chemical stability, strong hydrophobicity,easy chemical modification, etc.In this dissertation, two analytical methods were developed for the sensitivedetermination of some polutants by both magnetic solid phase extraction and micro-solidphase extraction techniques with graphene as adsorbent, coupled with gaschromatography-mass spectrometry (GC-MS). This dissertation is mainly concerned withthe following aspects:1. In this paper, a graphene-based magnetic nanocomposites (G-Fe3O4) wassynthesized and used as adsorbent for the extraction of some triazole fungicides incucumber and cabbage samples prior to GC-MS detection. Various experimentalparameters affecting the extraction efficiencies, such as the amount of G-Fe3O4, extractiontime, pH and salt concentration of the sample solution, and desorption conditions wereinvestigated. Under the optimized experimental conditions, the enrichment factors (EF) ofthe method for the analytes were in the range from461to697. The limits of detection (S/N=3) of the method for the analytes were between0.01and0.05ng/g. The recoveries of themethod for the seven triazoles were in the range from85.0%to108.2%with relativestandard deviations (RSDs) between3.4%and10.6%.2. A graphene-based magnetic nanocomposite (Fe3O4@SiO2-G) was synthesized andused as the adsorbent for the extraction of fourteen pesticides in tomato and rape samples prior to their GC-MS detection. Various experimental parameters affecting the extractionefficiencies, such as the amount of the Fe3O4@SiO2-G, extraction time, the pH and saltconcentration of the sample solution and desorption conditions were investigated. Underthe optimized experimental conditions, the limits of detection (S/N=3) of the method forthe compounds were between0.005and0.030ng/g for the vegetable samples. Goodreproducibilities were obtained with the RSDs below12.5%(n=5). The recoveries of themethod were in the range between83.2%and110.3%.3. A simple and novel hydrophilic polyamide membrane protected micro-solid phaseextraction method using graphene oxide as sorbent was developed for the enrichment ofparabens from bottled water and vinegars prior to GC-MS detection. Various experimentalparameters affecting the extraction efficiencies, such as the type and amount ofnanomaterial sorbents, extraction time, stirring rate, salt addition, sample solution pH anddesorption conditions, were investigated. Under the optimized experimental conditions, thelimits of detection (S/N=3) of the method were in the range of0.005-0.010ng/mL forwater samples and0.01-0.05ng/mL for vinegar samples, respectively. The recoveries ofthe method at spiking levels of5.0and70.0ng/mL were between84.6%and106.4%withthe relative standard deviations varying from4.2%to9.5%. The results indicated that theproposed method is a practical approach for the determination of parabens residues in realsamples. |
