| Microwave-assisted extraction （MAE） as a fast and efficient extraction technology hasbeen widely applied in food analysis, pharmaceutical analysis, and environmental analysis.Compared with static MAE mode, dynamic MAE （DMAE） has more advantages, it canaccelerate the transfer rate of analytes from sample matrix into extraction solvent.Moreover, the degradation of analytes could be avoided when increasing microwaveirradiation time in DMAE, since the analytes could be transferred out of the extractionvessel as soon as they were extracted. The DMAE is also suitable for on-line coupling withothers sample pretreatment techniques, thus sample pretreatment time was reduced andanalysis efficiency was effectively improved.In this thesis, a high-throughput DMAE technique was developed. The extractionsolvent for the15–20samples was delivered only by a vacuum pump instead of thehigh-pressure pump and peristaltic pump which are used in traditional DMAE to deliverextraction solvent, thus the costing of the device was reduced dramatically and manualhandling was simpler. This technique was coupled with related sample pretreatmenttechniques for analysis of harmful substances in food and environmental sample. The maincontents and results of this thesis are as followed:1. A method was developed based on on-line coupling of DMAE to solid-phaseextraction （SPE）, and was used for the determination of nicotine in mushroom sample. Nicotine was first extracted from the mushroom samples with water as extraction solutionunder the action of microwave energy, and then directly introduced into the SPE columnwhich was packed with cation-exchange resins. Subsequently, the nicotine trapped on theresins was eluted with methanol–ammonia （95:5, v/v） and determined by high-performanceliquid chromatography. Compared with traditional DMAE, the sample throughput andmicrowave energy utilization were improved by the proposed method, up to20samplescould be treated simultaneously in9min, and the extraction, separation and enrichment ofnicotine were completed in a single step. The limit of detection of nicotine obtained is5.6μg kg-1in fresh mushroom sample. The recovery of nicotine in mushroom samples is in therange of87.4–104.0%.2. An analytical method of DMAE combined with solidification of floating organicdrop （SFO） was developed for determining the five triazine herbicides in cereals. Theapproach combines the advantages of DMAE and SFO technique, and up to15samples canbe treated simultaneously in16min. Firstly, triazine herbicides were extracted with1mLof methanol containing90μL of1-dodecanol and following with10mL of water under theaction of microwave energy. After that,1.5g sodium chloride was added into the obtainedextract, and the mixture was centrifuged and cooled. The1-dodecanol drop whichcontained the target analytes was solidified and transferred for analysis by HPLC-UV.Limits of detection of the five triazines obtained were in the range of1.1–1.5ng g-1.Relative standard deviations of intra-and inter-day tests ranging from5%to7%wereobtained. The method was successfully applied to the analysis of ten cereals and therecoveries of the triazines for the spiked samples were in the range of80–102%.3. A sample pretreatment method was proposed for determination of steroid hormonesin fish tissues by coupling dynamic microwave-assisted extraction with salting-outliquid-liquid extraction. The steroid hormones in fish tissues were successively extractedwith5mL acetonitrile and about6mL water under the action of microwave energy.Subsequently, the extract was separated into an acetonitrile phase and an aqueous phasewith ammonium acetate. The acetonitrile phase containing the target analytes wasconcentrated and determined by LC-MS/MS. The limits of detection for the steroidhormones were in the range of0.030.15ng g-1. This method was successfully applied to analyze seven kinds of fish tissues, and the recoveries of the steroid hormones for thespiked samples were in the range of75.3±4.9%to95.4±6.2%. Compared with thetraditional method, the proposed method could reduce the consumption of the organicsolvent, shorten the sample preparation time, and increase the sample throughput.4. A green method was proposed for determination of ten sulfonamides （SAs） in soilsby dynamic microwave-assisted micellar extraction. The method used non-ionic surfactantTriton X-114as the extraction medium to extract the SAs from soil samples. Then sodiumchloride was added into the extract and the mixture was equilibrated. The analytes in thesurfactant-rich phase were concentrated with the help of centrifugation and directlyanalyzed by HPLC-UV. None of potentially hazardous organic solvents was used in thewhole sample preparation procedure, and the preparation time of15samples was about18min. The limits of detection for the SAs were in the range of0.420.68ng g-1. The relativestandard deviations of intra-and inter-day tests ranging from3.7%to5.9%and from4.3%to6.6%are obtained, respectively. Under the optimum conditions, the recoveries of tenSAs by analyzing five spiked soil samples were between69.7%and94.2%. The ageingeffect of spiked soil samples on the SAs recoveries was examined by the proposed method,and the results demonstrate that eight SAs could persist in five soils for three months.According to the classical theory of chemical kinetics, the relationship among extractiontemperature, extraction time and recoveries of SAs was studied. The reaction order, rateconstant and activation energy that parameter of kinetics were obtained based onexperimental analysis, which could express the rate of reaction system. The activationenergy of MAE for SAs was higher than water bath extraction, which shows that MAEreduces the energy required for extraction. |
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