Novel Liquid Phase Microextraction Methods And Its Application In The Analysis Of Fungicides Residues

Sample preparation is an essential step in the analysis of organic contaminant residues in food and environmental samples. The purpose of sample preparation is to separate and concentrate the target analytes from the complex sample matrix, thus reducing or eliminating the interferences of impurity in the sample to achieve the determination of analytes. In recent years, with the development of science and technology, people put forward higher requirements for the analytical accuracy. How to establish a simple and efficiency sample preparation methodologies have attracted much attention.Liquid-phase microextraction technique was developed on the basis of the traditional liquid extraction, which is a new sample pretreatment technology. LPME combined extraction, separation and concentration in one step. Meanwhile, LPME holds many advantages, such as low consumption of organic solvent, low cost. In addition, LPME provides an environmentally friendly technique. In this paper, three new liquid microextractions were developed for the determination of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water and juice samples followed by high performance liquid chromatography (HPLC). The main research contents were listed as follow:1. A DSME-SDBE with HPLC was developed for determination of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water and juice samples. In the proposed method, tridecane was selected as extractant, with magnetic stirring, tridecane mixed thoroughly with the sample solution. Stand for several minutes, phase separation was happened. Then, acetonitrile was carefully injected into the extracant membrane to form a stable droplet, back extraction was performed. Subsequently, single drop was taken into a microsyringe and injected into the HPLC system. In the process of single drop back extraction, the target was further extracted, so that the enrichment factor increased2-3folds. Under optimal conditions, EFs for three fungicides were in the range of201to236. The limits of detection for azoxystrobin, diethofencarb and pyrimethanil were0.09,0.18and0.24μg L-1, respectively. Reasonable relative recoveries were varied from84.4%to115.2%. The established method has successfully applied for the detection of fungicides in real samples.2. A DLLME-SDBE with HPLC was developed to the detection of azoxystrobin, diethofencarb and pyrimethanil in juice samples. Low density solvent (tridecane) was used as extractant and injected into the sample solution with acetone as disperser. A thin layer of the extractant formed on the top of the aqueous phase by centrifugation. Then, acetonitrile was carefully injected into the extracant membrane to form a stable droplet, back extraction was performed. Subsequently, single drop was taken into a microsyringe and injected into the HPLC system. Compared with dispersive liquid-liquid microextraction with solidification of floating organic droplet, the process of single drop back extraction instead of solidification of organic droplet, so that the enrichment factor increased2-4folds. Meanwhile, no need extractant ice bath, transfer and dissolution step, so the experimental operation is simpler. Under optimal conditions, EFs for three fungicides were in the range of180-316. The limits of detection for azoxystrobin, diethofencarb and pyrimethanil were0.36,0.15and0.45μg L-1, respectively. Reasonable relative recoveries were varied from86.6%to116.7%. This technique was eventually applied for the determination of three fungicides residues in juice samples.3. A low-density solvent air-assisted liquid-liquid microextraction with HPLC was developed for the determination of azoxystrobin, diethofencarb and pyrimethanil in water and juice samples. First, a narrow-neck glass tube was used to facilitate collection of the low-density solvent extraction. No use of disperser solvent. The mixture of extractant and sample solution is rapidly sucked into a5-mL glass syringe and then is injected into the narrow-neck glass tube and the procedure is repeated six times. A homogeneous solution was formed and then with the continuation injection of air by10-mL glass syringe, phase separation happened and the organic solvent was collected on the top of the solution. No centrifugation step was involved. Meanwhile, a shorter extraction time was obtained. Under optimal conditions, EFs for three fungicides were in the range of145to178. The limits of detection for azoxystrobin, diethofencarb and pyrimethanil were0.08,0.16and0.25μ L-1, respectively. Reasonable relative recoveries were varied from78.9%to108.0%. This method demonstrated to be fast, cheap, and successfully applied to the detection of trace fungicides in water and juice samples.