Development of counter current salting-out homogenous liquid-liquid extraction for isolation and preconcentration of some pesticides from aqueous samples.

In this paper, a new version of salting-out homogenous liquid-liquid extraction based on counter current mode combined with dispersive liquid-liquid microextraction has been developed for the extraction and preconcentration of some pesticides from aqueous samples and their determination by gas chromatography-flame ionization detection. In order to perform the method, aqueous solution of the analytes containing acetonitrile and 1,2-dibromoethane is transferred into a narrow bore tube which is filled partially with NaCl. During passing the solution through the tube, fine droplets of the organic phase are produced at the interface of solution and salt which go up through the tube and form a separated layer on the aqueous phase. The collected organic phase is removed and injected into de-ionized water for more enrichment of the analytes. Under the optimum extraction conditions, the method shows broad linear ranges for the target analytes. Enrichment factors and limits of detection for the selected pesticides are obtained in the ranges of 3480-3800 and 0.1-5μgL(-1), respectively. Relative standard deviations are in the range of 2-7% (n=6, C=50 or 100μgL(-1), each analyte). Finally, some aqueous samples were successfully analyzed using the developed method.

Farajzadeh MA ，Feriduni B ，Afshar Mogaddam MR 《-》

Development of a new extraction method based on counter current salting-out homogenous liquid-liquid extraction followed by dispersive liquid-liquid microextraction: Application for the extraction and preconcentration of widely used pesticides from fruit

In this paper, a new extraction method based on counter current salting-out homogenous liquid-liquid extraction (CCSHLLE) followed by dispersive liquid-liquid microextraction (DLLME) has been developed for the extraction and preconcentration of widely used pesticides in fruit juice samples prior to their analysis by gas chromatography-flame ionization detection (GC-FID). In this method, initially, sodium chloride as a separation reagent is filled into a small column and a mixture of water (or fruit juice) and acetonitrile is passed through the column. By passing the mixture sodium chloride is dissolved and the fine droplets of acetonitrile are formed due to salting-out effect. The produced droplets go up through the remained mixture and collect as a separated layer. Then, the collected organic phase (acetonitrile) is removed with a syringe and mixed with 1,1,2,2-tetrachloroethane (extraction solvent at µL level). In the second step, for further enrichment of the analytes the above mixture is injected into 5 mL de-ionized water placed in a test tube with conical bottom in order to dissolve acetonitrile into water and to achieve a sedimented phase at µL-level volume containing the enriched analytes. Under the optimal extraction conditions (extraction solvent, 1.5 mL acetonitrile; pH, 7; flow rate, 0.5 mL min(-1); preconcentration solvent, 20 µL 1,1,2,2-tetrachloroethane; NaCl concentration; 5%, w/w; and centrifugation rate and time, 5000 rpm and 5 min, respectively), the extraction recoveries and enrichment factors ranged from 87% to 96% and 544 to 600, respectively. Repeatability of the proposed method, expressed as relative standard deviations, ranged from 2% to 6% for intra-day (n=6, C=250 or 500 µg L(-1)) and inter-days (n=4, C=250 or 500 µg L(-1)) precisions. Limits of detection are obtained between 2 and 12 µg L(-1). Finally, the proposed method is applied for the determination of the target pesticide residues in the juice samples.

Farajzadeh MA ，Feriduni B ，Mogaddam MR 《-》

Countercurrent Salting-out Homogenous Liquid-Liquid Extraction and Dispersive Liquid-Liquid Microextraction Based on the Solidification of Floating Organic Drop Followed by High-Performance Liquid Chromatography for the Isolation and Preconcentration of P

Pesticides are widely used to control pests and prevent diseases in crops, including cereals, vegetables, and fruits. Due to factors such as the persistence of pesticides, bioaccumulation, and potential toxicity, pesticide residue monitoring in foodstuffs is very important. In the current research, we proposed a novel approach using countercurrent salting-out homogenous liquid-liquid extraction combined with dispersive liquid-liquid microextraction based on the solidification of floating organic droplets (DLLME-SFO) for isolation and preconcentration of pesticides from aqueous samples for analysis by high-performance liquid chromatography-ultraviolet detection (HPLC-UV). In brief, sodium chloride was used as a separation reagent, in a small glass column, through which was passed a mixture of an aqueous solution of, for example, fruit juice and acetonitrile. In this process, the droplets rose through the column and a separated layer would be formed on the remained an aqueous phase. Following that, acetonitrile as the organic phase was mixed with 50.0 µL of 1-undecanol (extraction solvent). To further enrich the analytes, the mixture was injected into 5 mL of a 4% w/v sodium chloride solution and placed in a tube for the DLLME-SFO. Under optimal conditions, a dynamic linear range of 0.5-500 μg/L, extraction recovery of 65-85%, enrichment factors of 108-142, and limit of detection of 0.2-0.4 μg/L were obtained for the organophosphorus pesticides analysed. In addition, the repeatability and reproducibility from five replicate measurements of the pesticides (100 μg/L) were within the ranges of 3.5-5.1% and 4.5-6.3%, respectively . In this research, a new extraction method based on countercurrent salting out homogeneous liquid-liquid extraction combined with DLLME-SFO has been applied for the determination of pesticide residues in fruits, juice and environmental samples before using HPLC-UV analysis. The combined method not only leads to high enrichment factors, but can also be used in complex matrices (such as fruits, juices and high-salt solutions) without pre-treatment or dilution. Compared with other sample preparation methods, this analysis procedure has many advantages, including simplicity, ease of operation, high pre-enrichment factor, low detection limit and relatively short analysis time. Combination of CCSHLLE and DLLME-SFO was applied for the analysis of organophosphorous pesticide residues in fruit, fruit juices and environmental samples. The DLLME-SFO method avoided using high density and toxic extraction solvents. LODs are achievable at ng L-1 using CCSLLE-DLLME-SFO-HPLC-UV.

Teymori Z ，Sadeghi M ，Fattahi N 《-》

Extraction and preconcentration technique for triazole pesticides from cow milk using dispersive liquid-liquid microextraction followed by GC-FID and GC-MS determinations.

A simple and rapid dispersive liquid-liquid microextraction (DLLME) technique coupled with gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS) was developed for the extraction, preconcentration, and analysis of triazole pesticides (penconazole, hexaconazole, tebuconazole, triticonazole, and difenoconazole) in cow milk samples. Initially to 5 mL milk sample, NaCl and acetonitrile were added as salting-out agent and extraction solvent, respectively. After manual shaking, the mixture was centrifuged. In the presence of sodium chloride, a two-phase system was formed: upper phase, acetonitrile containing triazole pesticides and lower phase, aqueous phase containing soluble compounds and the precipitated proteins. After the extraction of pesticides from milk, a portion of supernatant phase (acetonitrile) was removed, mixed with chloroform at microliter level and rapidly injected by syringe into 5 mL distilled water. In this process, triazole pesticides were extracted into fine droplets of chloroform (as extraction solvent). After centrifugation, the fine droplets of chloroform were sedimented in bottom of the conical test tube. Finally, GC-FID and GC-MS were used for the separation and determination of analytes in the sedimented phase. Some important parameters like type of solvent for extraction of pesticides from milk, salt amount, the volume of extraction solvent, etc., which affect the extraction efficiency, were completely studied. Under the optimum conditions, enrichment factors were in the range of 156-380. The linear ranges of calibration curves were wide and limits of detection (LODs) and limits of quantification (LOQs) were between 4-58 and 13-180 μg/L, respectively. This method is very simple and rapid, requiring <15 min for sample preparation.

Farajzadeh MA ，Djozan D ，Mogaddam MR ，Bamorowat M ... -  《-》

Development of a new dispersive liquid-liquid microextraction method in a narrow-bore tube for preconcentration of triazole pesticides from aqueous samples.

In the present work a new, simple, rapid and environmentally friendly dispersive liquid-liquid microextraction (DLLME) method has been developed for extraction/preconcentration of some triazole pesticides in aqueous samples and in grape juice. The extract was analyzed with gas chromatography-flame ionization detection (GC-FID) or gas chromatography-mass spectrometry (GC-MS). The DLLME method was performed in a narrow-bore tube containing aqueous sample. Acetonitrile and a mixture of n-hexanol and n-hexane (75:25, v/v) were used as disperser and extraction solvents, respectively. The effect of several factors that influence performance of the method, including the chemical nature and volume of the disperser and extraction solvents, number of extraction, pH and salt addition, were investigated and optimized. Figures of merit such as linearity (r(2)>0.995), enrichment factors (EFs) (263-380), limits of detection (0.3-5 μg L(-1)) and quantification (0.9-16.7 μg L(-1)), and relative standard deviations (3.2-5%) of the proposed method were satisfactory for determination of the model analytes. The method was successfully applied for determination of target pesticides in grape juice and good recoveries (74-99%) were achieved for spiked samples. As compared with the conventional DLLME, the proposed DLLME method showed higher EFs and less environmental hazards with no need for centrifuging.

Farajzadeh MA ，Djozan D ，Khorram P 《-》