| Derivatization of analytes is typically required before chromatographic analysisin order to obtain desirable chromatographic performances or improve the stability ofthe analytes and detectability of the method. Nevertheless, these derivatizationprocesss typically require reaction time from30min up to several hours at elevatedtemperature. In contrast, microwave protocols have demonstrated to be able to reducethe time required for derivatization to a few minutes, and can thus very effectivelyshorten the overall analysis time. The microwave assisted derivatization should beespecially suitable to the high-throughput analysis. In this thesis, microwave-assistedderivatization was applied to the treatment of environmental and food samples.In Introduction, the principles, characteristics and applications ofmicrowave-assisted derivatization and liquid phase microextraction were reviewed.In Chapter2, a new microwave-assisted derivatization method was developed forrapid derivatization of13natural sex hormones in feeds. Sex hormones were isolatedfrom the sample matrix by ultrasonic extraction coupled with solid-phase extraction,derived under microwave irradiation, and then analyzed directly by gaschromatography-mass spectrometry (GC-MS) in selective ion monitoring (SIM) mode.The key parameters affecting derivatization efficiency, including microwaveirradiation time, microwave power, and reaction solvent were studied. Whenmicrowave power was360W and microwave irradiation time was3min,13naturalsex hormones were simultaneously derived using heptafluorobutyric acid anhydride(HFBA) as derivatization reagent. This method was applied to the determination of13 natural sex hormones in different feed samples, and the obtained results werecompared with those obtained by the traditional thermal derivatization. The recoveriesfrom58.1to111%were obtained at sex hormone concentrations of10.00-300.00mg/kg with RSDs≤12.0%. The results showed that the present method was rapid,simple and efficient, and can be applied to the determination of13natural sexhormones in different feed samples.In Chapter3, the hollow fiber-based stirring sorptive bar liquid-liquidmicroextraction was applied to the extraction of hormones, including17-α-ethinylestradiol,17-α-estradiol, estriol,17-β-estradiol, estrone,17-α-hydroxyprogesterone, medroxyprogesterone, progesterone and norethisteroneacetate, in milk. The present method has the advantages of both hollow fiber-liquidphase microextraction and stirring bar sorptive extraction. The stirring sorptive barwas used as both the stirring bar of microextraction, and adsorber of the analytes,which can make extraction, clean-up and concentration be carried out in one step.When the extraction was completed, the stirring sorptive bar was easy isolated fromthe extraction system with the magnet. Several experimental parameters, such as thetype of extraction solvent, the number of hollow stirring sorptive bar, extraction time,stirring speed, ionic strength, and desorption conditions were investigated andoptimized. The analytes in the extract were derived and determined by gaschromatography mass spectrometry. The present method was applied to the analysisof milk samples, and the recoveries of analytes were in the range of93.6-104.6%withthe relative standard deviations ranging from1.6%to6.2%(n=5). The results showedthat the present method was a rapid, convenient and feasible method for thedetermination of hormones in milk samples.In Chapter4, the ionic liquid-based microwave-assisted dispersive liquid-liquidmicroextraction and derivatization was applied for the pretreatment of sixsulfonamides (SAs) prior to the determination by high-performance liquidchromatography (HPLC). By adding methanol (disperser), fluorescamine(derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction,derivatization, and preconcentration were continuously performed. Severalexperimental parameters, such as the type and volume of extraction solvent, the typeand volume of disperser, amount of derivatization reagent, microwave power,microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was240W, the analytescould be derived and extracted simultaneously within90s. The present method wasapplied to the analysis of some real samples, the recoveries of analytes in river water,honey, milk, and pig plasma samples were in the range of95.0-110.8%,95.4-106.3%,95.0-108.3%, and95.7-107.7%, respectively. The relative standard deviations variedbetween1.5%and7.3%(n=5). The results showed that the present method was arapid, convenient and feasible method for the determination of SAs in liquid samples.In Chapter5, a simple method based on simultaneous microwave-assistedderivatization and ionic liquid-based dispersive liquid-liquid microextraction isproposed for the derivatization, extraction and concentration of formaldehyde inbeverage samples prior to the determination by HPLC. Formaldehyde was in situderivatized with2,4-dinitrophenylhydrazine (DNPH) and simultaneously extractedand concentrated by using microwave-assisted derivatization and IL-based DLLME ina single step. Several experimental parameters, including type and volume ofextraction solvent, type and volume of disperser, microwave power and irradiationtime, volume of DNPH, pH of sample solution, and ionic strength were evaluated.When the microwave power was120W, formaldehyde could be derived and extractedsimultaneously only within90s. Under optimal experimental conditions, goodlinearity was observed in the range of0.50-50.00μg/L with the correlation coefficientof0.9965, and the limit of detection was0.12μg/L. The present method was appliedto the analysis of different beverage samples, and the recoveries of formaldehydeobtained were in the range of84.9-95.1%with the relative standard deviations lowerthan8.4%. The results showed that the present method was a rapid, convenient andfeasible method for the determination of formaldehyde in beverage samples.In Chapter6, a green and simple method, ionic liquid-based microwave-assistedsurfactant-improved dispersive liquid-liquid microextraction and derivatization wasdeveloped for the extraction and derivatization of aminoglycosides in milk samples.Nonionic surfactant Triton X-100and ionic liquid1-hexyl-3-methylimidazoliumhexafluorophosphate were used as the disperser and extraction solvent, respectively.Extraction, concentration, and derivatization of aminoglycosides were carried out in asingle step. Several experimental parameters, including type and volume of extractionsolvent, type and concentration of surfactant, microwave power and irradiation time,concentration of derivatization reagent, and pH value and volume of buffer wereinvestigated and optimized. Under the optimum experimental conditions, the linearities for determining the analytes were in the range0.40-10.00μg/L fortobramycin,1.00-25.00μg/L for neomycin, and2.00-50.00μg/L for gentamicin, withthe correlation coefficients ranging from0.9991to0.9998. The LODs for the analyteswere between0.11and0.50μg/L. The present method was applied to the analysis ofdifferent milk samples, and the recoveries of aminoglycosides obtained were in therange96.4-105.4%with the RSDs lower than5.5%. The results showed that thepresent method was a rapid, convenient, and environmentally friendly method for thedetermination of aminoglycosides in milk samples. |
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