| Microwave-assisted extraction (MAE) has been widely used for the samplepretreatment of food, pharmaceutical and environmental samples, for its shortextraction time, high extraction efficiency and small amount of sample. DynamicMAE (DMAE), compared with static MAE mode, has more advantages. Thedegradation of thermolabile substances in the process of extraction could be avoidedby using DMAE, since the extracts could be timely transferred out of the extractionvessel, and the microwave irradiation time of thermolabile substances could bereduced. In addition, the DMAE can be easily on-line coupled with other samplepretreatment techniques and detection methods, the extraction, clean-up,concentration and determination of samples can be accomplished at one time, andsample pretreatment time was reduced and analysis efficiency was improved.In this paper, the application of high-throughput DMAE technique for theextraction of food and Chinese herbs samples has been studied. The technique wascoupled with other sample pretreatment techniques for rapid extraction, clean-up andconcentration of pesticide residue in food and efficacious components in Chineseherbs, such as solid-phase extraction and salting-out liquid-liquid extraction. Themain contents are as follows:1. A DMAE apparatus was presented for the extraction of flavonoids fromPlatycladus orientalis (L.) Franco. The optimized extraction conditions were asfollowed: extraction solvent,60%aqueous methanol; extraction time,8min; microwave power,350W; extraction solvent flow-rate,1.0mL min-1. The extractsobtained under the optimized extraction conditions were determined byhigh-performance liquid chromatography (HPLC) with an ultraviolet detector (UVD).The detection limits obtained was0.03μg mL-1. The relative standard deviations were3.1%-5.3%. Meanwhile, the method has been compared with pressurizedmicrowave-assisted extraction (PMAE), ultrasonic extraction (UE), heat refluxextraction (RE) and Soxhlet extraction (SOX). The results showed that the extractionyield of quercitrin obtained by HTDMAE was higher than that obtained by UE, REand SOX. Although the extraction yield obtained by HTDMAE and PMAE weresimilar, but HTDMAE was proceeding without increasing and descending pressureand the extraction time had been reduced dramatically.2. The DMAE coupled with solid-phase extraction was developed for extractionand clean-up of six triazine herbicides in rice, and LC-MS/MS was employed forquantitative analysis. The SPE column was packed with strong cation exchange (SCX)resin. The parameters which could affect the extraction effect were investigated. Theoptimized extraction conditions were as followed: extraction solvent,80%aqueousmethanol; microwave forward power,600W; extraction time,10min; extractionsolvent flow-rate,1.0mL min-1. The optimized SPE conditions were as followed:sulfonation time of SCX resin,40min; amount of resin packed into the SPE column,60mg; elution solvent,3.5mL methanol-ammonia (95:5, v/v); elution solventflow-rate,1.0mL min-1. The limit of detection for six triazine herbicides were in therange of0.10-0.31ng g-1. The recoveries of six triazine herbicides were in the rangeof82%-108%. The extraction, clean-up and enrichment of triazine herbicides could becompleted in a single step by the proposed method, and the sample preparation wasfaster and simpler.3. The DMAE coupled with salting-out liquid-liquid extraction was developed forextraction, clean-up and concentration of six triazine herbicides in tomatos. At first,the triazine herbicides in tomato samples were extracted by HTDMAE. Subsequently,the extract was cleaned-up and concentrated by salting-out liquid-liquid extraction,Finally, the extract was evaporated to dryness under a stream of N2and injected into the LC-MS/MS system for analysis. All the parameters which could affect theextraction effect were investigated. The optimized extraction conditions were asfollowed: extraction solvent,70%aqueous acetonitrile; microwave power,350W;extraction time,7min; extraction solvent flow-rate,1.0mL/min; pH value of theextract,8; salting-out reagent,2.0g ammonium acetate. The limits of detection for sixtriazine herbicides were0.08-0.33ng g-1. The recoveries of six triazine herbicides forthe spiked samples were in the range of80%-95%. This method has been successfullyapplied to rapid detection of triazine herbicides from tomatoes, the result wassatisfactory. |
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