Mingzhu Hu

Utilization of a novel microwave-assisted homogeneous ionic liquid microextraction method for the determination of Sudan dyes in red wines.

A novel microwave-assisted homogeneous ionic liquid microextraction (MA-HILME) method was first developed for the extraction of Sudan dyes in red wines followed by detection using high-performance liquid chromatography. 1-dodecyl-3-methylimidazolium bromide ([C12MIM]Br) was used as extractant in a microwave-assisted extraction (MAE) procedure, and then transferred into hydrophobic solid-state ionic liquid after adding ammonium hexafluorophosphate ([NH4][PF6]). The separation between liquid state sample and solid state extractant can be realized easily. Several experimental parameters, including type and amount of extraction solvent, microwave power and irradiation time, amount of ion-exchange reagent ([NH4][PF6]), pH of sample solution, and ionic strength, were evaluated. Under the optimum experimental conditions, the linearity for the determining of the analytes was in the range of 0.5-100 μg L(-1), with the correlation coefficients ranging from 0.9995 to 0.9999. The limits of detection for Sudan I, Sudan II, Sudan III, and Sudan IV were 0.19, 0.18, 0.24, and 0.16 μg L(-1), respectively. When the present method was applied to the determination of Sudan dyes in red wines, satisfactory recoveries were obtained in the range of 78.5-106.8%, and relative standard deviations were lower than 9.7%.

Application of magnetic solvent bar liquid-phase microextraction for determination of organophosphorus pesticides in fruit juice samples by gas chromatography mass spectrometry.

A simple, rapid and sensitive sample pretreatment technique, magnetic solvent bar liquid-phase microextraction (MSB-LPME) was developed for extracting organophosphorus pesticides from fruit juice. The analytes were extracted from the sample to the organic solvent immobilized in the fiber. The magnetic solvent bar not only can be used to stir the samples but also extract the analytes. After extraction, the analyte-adsorbed magnetic solvent bar can be readily isolated from the sample solution by a magnet, which could greatly simplify the operation and reduce the whole pretreatment time. The bar was eluted with methanol. The elute was evaporated to dryness and residue was dissolved in hexane. Several experimental parameters were investigated and optimized, including type of extraction solvent, number of magnetic solvent bar, extraction temperature, extraction time, salt concentration, stirring speed, pH and desorption conditions. The recoveries were in the range of 81.3-104.6%, and good reproducibilities were obtained with relative standard deviation below 6.1%.

Dynamic microwave-assisted extraction combined with continuous-flow microextraction for determination of pesticides in vegetables

A simple, rapid, solventless and cost-effective dynamic microwave-assisted extraction (DMAE) combined with continuous-flow microextraction (CFME) system was firstly assembled and validated for extraction of eight organophosphorus pesticides in vegetables. The method combines the advantages of DMAE and CFME, and extends the application of the single drop microextraction to complex solid samples. The extraction, separation, and enrichment were performed in a single step, which could greatly simplify the operation and reduce the whole pretreatment time. In the developed method, analytes were first extracted from the vegetables using 3% NaCl solution as extraction solvent, then concentrated into microextraction solvent. After extraction, the microextraction solvent containing the enriched analyte was directly analyzed by GC-MS without any filtration or clean-up process. Several parameters affecting the extraction efficiency were investigated and optimized. Real vegetable samples were analyzed, satisfactory recoveries were obtained in the range of 80.7-106.7%, and relative standard deviations were lower than 8.7%.

Dynamic microwave-assisted extraction online coupled with single drop microextraction of organophosphorus pesticides in tea samples

A new method for the determination of seven organophosphorus pesticides was developed using dynamic microwave-assisted extraction online coupled with single drop microextraction prior to gas chromatographic mass spectrometry (GC-MS). The method combines the advantages of dynamic microwave-assisted extraction and single-drop microextraction, which could greatly simplify the operation and reduce the whole pretreatment time. In the developed method, tea samples were extracted with 25% ethanol aqueous solution and purified with acidic alumina at the same time, and then the analytes were concentrated into microextraction solvent. When the extraction was completed, the solvent microdrop containing the enriched analytes was retracted into the microsyringe and directly analyzed by GC-MS without any filtration or cleanup step. The method makes extraction, cleanup, separation, and enrichment to be carried out in one step. Several experimental parameters, including type of extraction solvent, type and amount of dispersant, type and volume of microextraction solvent, microwave power, extraction time, and flow rate of extraction solvent were investigated and optimized. Under optimal experimental conditions, good linearity was observed in the range of 2.00-500.00 μg kg(-1). The limits of detection and quantification were in the range of 0.4-1.7 μg kg(-1) and 1.1-5.6 μg kg(-1), respectively. The present method was applied to the analysis of tea samples, and the recoveries of analytes were in the range of 84.9-106.4% with the relative standard deviations ranging from 1.0 to 6.1%. The results showed that the present method was a rapid and feasible method for the determination of organophosphorus pesticides in tea samples.

Ionic-liquid-impregnated resin for the microwave-assisted solid–liquid extraction of triazine herbicides in honey

Microwave-assisted ionic-liquid-impregnated resin solid-liquid extraction was developed for the extraction of triazine herbicides, including cyanazine, metribuzin, desmetryn, secbumeton, terbumeton, terbuthylazine, dimethametryn, and dipropetryn in honey samples. The ionic-liquid-impregnated resin was prepared by immobilizing 1-hexyl-3-methylimidazolium hexafluorophosphate in the microspores of resin. The resin was used as the extraction adsorbent. The extraction and enrichment of analytes were performed in a single step. The extraction time can be shortened greatly with the help of microwave. The effects of experimental parameters including type of resin, type of ionic liquid, mass ratio of resin to ionic liquid, extraction time, amount of the impregnated resin, extraction temperature, salt concentration, and desorption conditions on the extraction efficiency, were investigated. A Box-Behnken design was applied to the selection of the experimental parameters. The recoveries were in the range of 80.1 to 103.4% and the relative standard deviations were lower than 6.8%. The present method was applied to the analysis of honey samples.

Microwave‐assisted liquid–liquid microextraction based on solidification of ionic liquid for the determination of sulfonamides in environmental water samples

An easy, quick, and green method, microwave-assisted liquid-liquid microextraction based on solidification of ionic liquid, was first developed and applied to the extraction of sulfonamides in environmental water samples. 1-Ethy-3-methylimidazolium hexafluorophosphate, which is a solid-state ionic liquid at room temperature, was used as extraction solvent in the present method. After microwave irradiation for 90 s, the solid-state ionic liquid was melted into liquid phase and used to finish the extraction of the analytes. The ionic liquid and sample matrix can be separated by freezing and centrifuging. Several experimental parameters, including amount of extraction solvent, microwave power and irradiation time, pH of sample solution, and ionic strength, were investigated and optimized. Under the optimum experimental conditions, good linearity was observed in the range of 2.00-400.00 μg/L with the correlation coefficients ranging from 0.9995 to 0.9999. The limits of detection for sulfathiazole, sulfachlorpyridazine, sulfamethoxazole, and sulfaphenazole were 0.39, 0.33, 0.62, and 0.85 μg/L, respectively. When the present method was applied to the analysis of environmental water samples, the recoveries of the analytes ranged from 75.09 to 115.78% and relative standard deviations were lower than 11.89%.

Integrated microwave processing system for the extraction of organophosphorus pesticides in fresh vegetables.

A simple and efficient integrated microwave processing system (IMPS) was firstly assembled and validated for the extraction of organophosphorus pesticides in fresh vegetables. Two processes under microwave irradiation, dynamic microwave-assisted extraction (DMAE) and microwave-accelerated solvent elution (MASE), were integrated for simplifying the pretreatment of the sample. Extraction, separation, enrichment and elution were finished in a simple step. The organophosphorus pesticides were extracted from the fresh vegetables into hexane with DMAE, and then the extract was directly introduced into the enrichment column packed with active carbon fiber (ACF). Subsequently, the organophosphorus pesticides trapped on the ACF were eluted with ethyl acetate under microwave irradiation. No further filtration or cleanup was required before analysis of the eluate by gas chromatography-mass spectrometry. Some experimental parameters affecting extraction efficiency were investigated and optimized, such as microwave output power, kind and volume of extraction solvent, extraction time, amount of sorbent, elution microwave power, kind and volume of elution solvent, elution solvent flow rate. Under the optimized conditions, the recoveries were in the range of 71.5-105.2%, and the relative standard deviations were lower than 11.6%. The experiment results prove that the present method is a simple and effective sample preparation method for the determination of pesticides in solid samples.

Microwave-assisted liquid–liquid microextraction based on solidification of floating organic droplet for the determination of triazines in honey samples

Microwave-assisted liquid–liquid microextraction based on solidification of floating organic droplet (MA-LLME-SFO) was first developed and applied to the extraction of triazines in honey samples. 1-Dodecanol, which is of low toxicity, low density and has an appropriate melting point near room temperature, was chosen as the extraction solvent. Furthermore, traditional organic dispersive solvents were avoided in this method with the aid of microwave irradiation. Several experimental parameters, including the type and volume of extraction solvent, microwave power and irradiation time, pH of the sample solution, ionic strength and centrifugation rate were investigated and optimized. The proposed method showed a good linearity within the range of 5.00–250.00 μg kg−1 with the correlation coefficients ranging from 0.9994 to 0.9998. The limits of detection for cyanazine, desmetryn, terbuthylazine and dimethametryn were 1.39, 0.95, 1.20, and 1.07 μg kg−1, respectively. The recoveries of the analytes ranged from 74.84 to 112.74% and the relative standard deviations were lower than 13.10%, when the present method was applied to the analysis of real samples.