Novel solvent-free microwave-assisted extraction coupled with low-density solvent-based in-tube ultrasound-assisted emulsification microextraction for the fast analysis of organophosphorus pesticides in soils.

A novel and rapid solventless microwave-assisted extraction coupled with low-density solvent-based in-tube ultrasound-assisted emulsification microextraction has been developed for the efficient determination of nine organophosphorus pesticides in soils by GC analysis with microelectron capture detection. A specially designed, homemade glass tube inbuilt with a scaled capillary tube was used as an extraction device to collect and measure the separated extractant phase easily. Parameters affecting the efficiencies of the developed method were thoroughly investigated. From experimental results, the following conditions were selected for the extraction of organophosphorus pesticides from 1.0 g of soil sample to 5 mL of aqueous solution under 226 W of microwave irradiation for 2.5 min followed by ultrasound-assisted emulsification microextraction with 20 µL toluene for 30 s and then centrifugation at 3200 rpm for 3 min. Detections were linear in the range of 0.25-10 ng/g with detection limits between 0.04 and 0.13 ng/g for all target analytes. The applicability of the method to real samples was assessed on agricultural contaminated soils and the recoveries ranged between 91.4 and 101.3%. Compared to other methods, the present method was shown to be highly competitive in terms of sensitivity, cost, eco-friendly nature, and analysis speed.

Determination of organophosphorous pesticides in water using in-syringe ultrasound-assisted emulsification and gas chromatography with electron-capture detection.

An in-syringe ultrasound-assisted emulsification microextraction (USAEME) was developed for the extraction of organophosphorus pesticides (OPPs) from water samples. The OPPs subsequently analyzed gas chromatography (GC) using a microelectron capture detector (muECD). Ultrasound radiation was applied to accelerate the emulsification of microL-level low-density organic solvent in aqueous solutions to enhance the microextraction efficiency of OPPs in the sample preparation for GC-muECD. Parameters affecting the efficiency of USAEME, such as the extraction solvent, solvent volume, pH, salt-addition, and extraction time were thoroughly investigated. Based on experimental results, OPPs were extracted from a 5mL aqueous sample by the addition of 20microL toluene as the extraction solvent, followed by ultrasonication for 30s, and then centrifugation for 3min at 3200rpm, offered the best extraction efficiency. Detections were linear in the concentration of 0.01-1microg/L with detection limits between 1ng/L and 2ng/L for OPPs. Enrichment factors ranged from 330 to 699. Three spiked aqueous samples were analyzed, and recovery ranged from 90.1% to 104.7% for farm-field water, and 90.1% to 101.8% for industrial wastewater. The proposed method provides a simple, rapid, sensitive, inexpensive, and eco-friendly process for determining OPPs in water samples.

In-capillary derivatization and stacking electrophoretic analysis of gamma-aminobutyric acid and alanine in tea samples to redeem the detection after dilution to decrease matrix interference.

An in-capillary derivatization and stacking capillary electrophoresis (CE) technique has been applied to redeem the detection of dilute analytes in the analysis of gamma-aminobutyric acid (GABA) and alanine (Ala) in tea samples. Extracts from samples were diluted to eliminate matrix interference before introduction into the CE system. GABA and Ala in the diluted sample zone were derivatized with o-phthaldialdehyde/2-mercaptoethanol (OPA/2-ME) to form fluorescence-labeled products in the stacking process, and the labeled derivatives were then enriched by online stacking. Optimal conditions for the stacking, such as the concentration of the background buffer solution, the matrix of the sample zone (sample solution), and the volume of the sample injection, were investigated and then applied to real sample analysis. Under optimum conditions, the detections were linear in the range of 5.0 nM-2.5 microM with the square of correlation coefficients (R2) of 0.9995 and 0.9992 for GABA and Ala, respectively. Detection limits were found to be 0.7 and 0.8 nM for GABA and Ala, respectively. Tea samples were analyzed with recoveries between 92.33 and 97.87% and between 94.36 and 96.46% for GABA and Ala, respectively. This method is a rapid, convenient, and sensitive process for determining GABA and Ala in complicated matrix samples such as tea samples.

New cloud vapor zone (CVZ) coupled headspace solid-phase microextraction technique.

A new cloud vapor zone (CVZ)-based headspace solid-phase microextraction (HS-SPME) technique has been demonstrated with the capability of heating the sample matrix and simultaneously cooling the sampling zone. A bi-temperature-controlled (BTC) system, allowing 10 mL of test sample heating and headspace external-cooling, was employed for the CVZ formation around the SPME-fiber sampling area. In the CVZ procedure, the heated headspace vapor undergoes a sudden cooling near the SPME to form a dense cloud of analyte-water vapor, which is helpful for adsorption or absorption of the analyte. The device was evaluated for the quantitative analysis of aqueous chlorothalonil. Parameters influencing sampling efficiency, e.g., SPME fiber coating, SPME sampling temperature and time, solution modifier, addition of salt, sample pH, and temperature, were investigated and optimized thoroughly. The proposed BTC-HS-SPME method afforded a best extraction efficiency of above 94% accuracy (less than 4.1% RSD, n=7) by using the PDMS fiber to collect chlorothalonil in the headspace at 5 degrees C under the optimized condition, i.e., heating sample solution (added as 10% ethylene glycol and 30% NaCl, at pH 7.0) at 130 degrees C for 15 min. The detection was linear from 0.01 to 80 microg L-1 with a regression coefficient of 0.9998 and had a detection limit of 3.0 ng L-1 based on S/N=3. Practical application was demonstrated by analyzing chlorothalonil in farm water samples with promising results and recoveries. The approach provided a very simple, fast, sensitive, and solvent-free procedure to collect analytes from aqueous solution. The approach can provide a new platform for other sensitive HS-SPME assays.

Capillary electrophoretic analysis of gamma-aminobutyric acid and alanine in tea with in-capillary derivatization and fluorescence detection.

The aim of this study was to investigate an in-capillary derivatization capillary electrophoresis (CE) technique that was performed to determine the concentration of gamma-aminobutyric acid (GABA) and alanine (Ala) in tea after being derivatized with o-phthaldialdehyde/2-mercaptoethanol (OPA/2-ME) to form fluorescence-labeled products. The conditions of labeled derivatization and CE separation were optimized and then applied to real sample analysis. The labeled derivatization with 20 mM OPA and 26.67 mM 2-ME (mol ratio=0.75) at pH 10 offered the most sensitive detection, and the separation with 30 mM sodium tetraborate buffer (pH 10.0) under 21 kV achieved good selectivity within 14 min. The detections were linear in the range of 0.05-5 microM with correlation coefficients (R2) of 0.9995 and 0.9964 and with detection limits of 0.004 and 0.02 microM for GABA and Ala, respectively. The recoveries were 94.22% (3.58% RSD) and 93.54% (6.46% RSD) for five determinations of GABA and Ala, respectively. This method is a fast, convenient, sensitive, and eco-friendly way to determine the GABA and Ala in tea samples from different manufacturing processes.

Determination of dichlorvos by on-line microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection.

The pretreatment technique of microwave-assisted extraction on-line headspace solid-phase microextraction (MAE-HS-SPME) was designed and studied for one-step in-situ sample preparation prior to the chromatographic analysis of a pesticide on vegetables. The pesticide on chopped vegetables was extracted into an aqueous solution with the aid of microwave irradiation and then directly onto the SPME fiber in headspace. After being collected on to the SPME fiber and desorbed in the GC injection port, the pesticide (dichlorvos) was analyzed with a GC-electron-capture detection system. The optimum conditions for obtaining extraction efficiency, such as the pH, the polarity modifier, and the salt added in sample solution, the microwave irradiation, as well as the desorption parameters were investigated. Experimental results indicated that the proposed MAE-HS-SPME technique attained the best extraction efficiency of 106% recovery under the optimized conditions, i.e. irradiation of extraction solution (10% aqueous ethylene glycol) at pH 5.0 with medium microwave power for 10 min. Desorption at 220 degrees C for 3 min offered the best detection result. The detection was linear at 5-75 microg/l with correlation coefficient of 0.9985. Detection limit was obtained at approximately 1.0 microg/l level based on S/N=3. The proposed method provided a very simple, fast, and solvent-less procedure to collect pesticides directly from vegetables for GC determination. Its application was illustrated by the analysis of trace dichlorvos in vegetables.