Dispersive Liquid Phase Microextraction With Innovative Dispersive Solvent For Pesticide Residue Analysis In Juice And Fruit

Dispersive liquid liquid microextraction (DLLME) is a popular mode of liquid phase microextraction (LPME) techniques, which is mainly used for the determination of the target analytes in aqueous matrix. In the method, with the existence of dispersive solvent, the extraction solvent is rapidly dispersed into the aqueous sample phase as fine droplets, which markedly increases the contact surface between phases and reduces the extraction time with the increasing enrichment factors. However, compared with the volume of the extraction solvent, the volume of organic dispersive solvent, such as methanol or acetonitrile, is relatively high (in the mL level). It could lead to a decrease in the partition coefficient of analytes in the extraction solvent for the solubility of the analytes increased in the sample solution. In this study, based on previous work, some innovative approaches about dispersive solvent in DLLME were carried out as follows:Using the chlorinated solvent as extraction solvent, the methods called surfactant assisted emulsification microextraction (SAEME) and air assisted liquid liquid microextraction (AALLME) were developed, with the free of organic diepersive solvent. In SAEME, the surfactant is used as emulsifier to enhance the dispersion of the water-immiscible phase into the aqueous phase by reducing the interfacial tension between the two phases. Combining with gas chromatography (GC), it was used to analyse7fungicide residues (procymidone, picoxystrobin, myclobutani, trifloxystrobin, epoxiconazole, difenoconazole, azoxystrobin) in apple juice and pear juice samples. Limits of detection (LOD) of the method were in the range of0.01-0.4μg L-1; In AALLME, the extraction solvent was rapidly dispersed into the aqueous samples by pulling in and pushing out the mixture of aqueous sample solution and extraction solvent with a syringe several times, in which no dispersive solvent was used. Combining with GC, it was used to determinate7fungicides (procymidone, picoxystrobin, myclobutani, trifloxystrobin, epoxiconazole, difenoconazole, azoxystrobin) and11organophosphorus pesticide residues (dichlorvos, phorate, diazinon, disulfoton, dimethoate, pirimiphos-methyl, fenitrothion, fenthion, quinalphos, phenthoate, methidathion) in apple juice and pear juice samples and the LOD were in the range of0.01-0.3μg L-1and0.02-0.6μg L-1, respectively.Using the extraction solvent of non-chlorine solvents with density lower than water and appropriate melting point near room temperature, two novel DLLME based on the solidification of a floating organic droplet were developed, in which the extractant layer on top of the aqueous sample could easily collected by solidifying it at low temperature. The first one was ultrasound-assisted surfactant-enhanced emulsification microextraction technique based on the solidification of a floating organic droplet (UASEME-SFO). It was validated for simultaneous determination of6fungicide residues (pyrimethanil, fludioxonil, procymidone, cyprodinil, kresoxim-methyl, pyraclostrobin) in apple juice and pear juice samples. The LOD of the method were0.4-1.4μg L-1. The second was air-assisted liquid-liquid microextraction technique based on the solidification of a floating organic droplet (AALLME-SFO). It was validated for the analysis of7fungicides (procymidone, picoxystrobin, myclobutani, trifloxystrobin, epoxiconazole, difenoconazole, azoxystrobin) in apple juice and pear juice samples. The LOD of the method were0.02-0.25μg-1.Using the environment-friendly ionic liquid as extraction solvent, three dispersive solvent-free methods were developed with the help of surfactant and air assistance. The first was vortex-assisted surfactant-enhanced emulsification microextraction based on ionic liquid (IL-VASEME) method, which was validated for the determination of4funficide residues (pyrimethanil, fludioxonil, cyprodinil, pyraclostrobin) in apple juice and grape juice samples. The LOD were0.6-2.0μg L-1. The second was manual shaking-ultrasound assisted-surfactant enhanced emulsification microextraction (IL-MS-UASEME) method, validated for the determination of3funficide residues (pyrimethanil, fludioxonil, cyprodinil) in apple juice and grape juice samples. The LOD were0.4-1.6μg L-1. The third one was a novel AALLME based on ionic liquid (IL-AALLME) method, which was a validated for the determination of5funficide residues (pyrimethanil, fludioxonil, azoxystrobin, cyprodinil, pyraclostrobin) in apple juice, pear juice and grape juice samples. The LOD were0.4-1.8μg L-1.DLLME method was extended to the grape sample, rather than aqueous sample. The acetonitrile extractant in QuEChERS (acronym of quick, easy, cheap, effective, rugged, and safe) method could be the dispersive solvent in DLLME based on the solidification of a floating organic droplet (DLLME-SFO). The combination of DLLME and QuEChERS was developed for the determination of6fungicide residues (pyrimethanil, fludioxonil, procymidone, iprodione, cyprodinil, kresoxim-methyl) in grape samples. The LOD were0.2-2mg kg-1.To sum up,7novel dispersive liquid phase microextraction techniques were developed which dispersed the extraction solvent with the help of surfactant-enhanced emulsification or air assistance. These methods were simple to operate, decreased or even avoided the use of high toxic extraction solvent and dispersive solvent in conventional DLLME, DLLME-SFO and IL-DLLME. In addition, the application of DLLME-SFO in solid grape matrix was also explored.