Sample preparation method for the analysis of some organophosphorus pesticides residues in tomato by ultrasound-assisted solvent extraction followed by dispersive liquid-liquid microextraction.

A very simple and economic method for organophosphorus pesticides (OPPs) residues analysis in tomato by means of gas chromatography-flame photometric detection (GC-FPD) has been developed. The method involves a rapid and small-scale extraction. The sample was homogenised and extraction of the OPPs with acetone was carried out assisted by sonication. No clean-up or evaporation were required after extraction. Pre-concentration of the OPPs from the acetone extract was done by using dispersive liquid-liquid microextraction (DLLME) technique. Chlorobenzene was added in micro-level volume as extraction solvent and triphenylphosphate as internal standard in DLLME procedure. The method showed good linearity over the range assayed (0.5-1000µgkg(-1)) and the detection limits for the pesticides studied varied from 0.1 to 0.5µgkg(-1). Repeatability studies resulted a relative standard deviation lower than 10% in all cases. The proposed method was used to determine pesticides levels in tomatoes grown in open field.

Speciation of butyl and phenyltin compounds using dispersive liquid-liquid microextraction and gas chromatography-flame photometric detection.

Dispersive liquid-liquid microextraction and gas chromatography-flame photometric detection (DLLME-GC-FPD) were performed for the speciation of butyl and phenyltin compounds in water samples after derivatization with sodium tetraethylborate (NaBEt4). Some important parameters, such as pH, amount of NaBEt4, derivatization time, kind and volume of extraction and disperser solvents, extraction time and salt effect were investigated and optimized. High enrichment factors (825-1036) and low detection limits (0.2-1 ng L(-1)) were obtained under the optimum conditions. The calibration graphs were linear in the range of 0.5-1000 ng L(-1) (as Sn) for the target analytes. The relative standard deviations (RSDs) for the extraction of 20 ng L(-1) (as Sn) of butyl and phenyltin compounds varied from 2.3 to 5.9% (n=7) and from 4.1 to 8.8% (n=7) with and without using internal standard, respectively. Seawater and river water samples were successfully analyzed using the proposed method and the relative recoveries of the studied compounds in the water samples, at spiking levels of 10.0 and 100 ng L(-1) (as Sn) were obtained to be 82.5-104.7%.

Development of a dispersive liquid-liquid microextraction method for the determination of polychlorinated biphenyls in water.

A very simple and powerful microextraction procedure, the dispersive liquid-liquid microextraction (DLLME), was used for the determination of the content of 10 polychlorinated biphenyls (PCBs) in water samples, using gas chromatography coupled with electron-capture detection (GC-ECD). The appropriate amount of acetone (disperser solvent) and chlorobenzene (extraction solvent) at the microlevel volume was used for this procedure. The conditions for the microextraction performance were investigated and optimized. The optimized method exhibited a good linearity (R(2)>0.996) over the studied range (0.005-2 microg L(-1)), illustrating a satisfactory precision level with R.S.D. values between 4.1% and 11.0%. The values of the detection limit (S/N=3) were found to be lower than 0.002 microg L(-1). Furthermore, a large enrichment factor for the analytes (up to a 540-fold) was achieved in a very short time for only a 5.00-mL water sample. The effectiveness of the method towards real samples was tested by analyzing well, river and seawater samples. The relative recoveries of the well, river and seawater samples, which had been spiked with different levels of PCBs were equal to 92.0-114.0%, 97.0-102.0% and 96.0-103.0%, respectively. The attained results demonstrated that DLLME combined with GC-ECD was a fast and inexpensive technique for the PCBs determination in water samples.

A novel methodology based on solvents less dense than through dispersive liquid-liquid microextraction: application in quantitation of in fruit juices and soft drinks by fiber optic-linear array detection spectrophotometry.

In this study a novel methodology is proposed for utilizing solvents less dense than water by using a dispersive liquid-liquid microextraction (DLLME) technique. Conventional microextraction vessels and facile strategy have been used. We have avoided using routine microextraction solvents in the DLLME procedure that are mostly chlorinated, dense, environmentally hazardous and expensive which limits the application of this method to some extent. The aforesaid process has been combined with fiber optic-linear array detection spectrophotometry (FO-LADS) with charge-coupled device (CCD) detector benefiting of a micro-cell. l-Ascorbate was selected as a model compound and the proposed method was carried out for preconcentration and assay of iodine produced by reduction of potassium iodate in fruit juices, soft drinks and pharmaceutical preparations. The influences of the various analytical parameters on the microextraction procedure and oxidation reaction have been evaluated and optimized. The accuracy of the method was confirmed by parallel analyses as the reference method (ISO 6557/2). The calibration curve was linear in the range of 1.76-26.40 µg mL-1 of l-ascorbate with a correlation coefficient (r) of 0.9912. The LOD obtained from the calibration curve was 0.40 µg mL-1.

Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry: ultra trace determination of cadmium in water samples.

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 microL methanol (disperser solvent) containing 34 microL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25+/-1 microL). Then a 20 microL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-20 ng L(-1) with detection limit of 0.6 ng L(-1). The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L(-1) of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L(-1) are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid-liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).