Determination of triazine herbicides in aqueous samples by dispersive liquid-liquid microextraction with gas chromatography-ion trap mass spectrometry

A simple and rapid new dispersive liquid-liquid microextraction technique (DLLME) coupled with gas chromatography-ion trap mass spectrometric detection (GC-MS) was developed for the extraction and analysis of triazine herbicides from water samples. In this method, a mixture of 12.0 microL chlorobenzene (extraction solvent) and 1.00 mL acetone (disperser solvent) is rapidly injected by syringe into the 5.00 mL water sample containing 4% (w/v) sodium chloride. In this process, triazines in the water sample are extracted into the fine droplets of chlorobenzene. After centrifuging for 5 min at 6000 rpm, the fine droplets of chlorobenzene are sedimented in the bottom of the conical test tube (8.0+/-0.3 microL). The settled phase (2.0 microL) is collected and injected into the GC-MS for separation and determination of triazines. Some important parameters, viz, type of extraction solvent, identity and volume of disperser solvent, extraction time, and salt effect, which affect on DLLME were studied. Under optimum conditions the enrichment factors and extraction recoveries were high and ranged between 151-722 and 24.2-115.6%, respectively. The linear range was wide (0.2-200 microg L(-1)) and the limits of detection were between 0.021 and 0.12 microg L(-1) for most of the analytes. The relative standard deviations (RSDs) for 5.00 microg L(-1) of triazines in water were in the range of 1.36-8.67%. The performance of the method was checked by analysis of river and tap water samples, and the relative recoveries of triazines from river and tap water at a spiking level of 5.0 microg L(-1) were 85.2-114.5% and 87.8-119.4%, respectively. This method was also compared with solid-phase microextraction (SPME) and hollow fiber protected liquid-phase microextraction (HFP-LPME) methods. DLLME is a very simple and rapid method, requiring less than 3 min. It also has high enrichment factors and recoveries for the extraction of triazines from water.     

Determination of organic compounds in water using dispersive liquid-liquid microextraction

A new microextraction technique termed dispersive liquid-liquid microextraction (DLLME) was developed. DLLME is a very simple and rapid method for extraction and preconcentration of organic compounds from water samples. In this method, the appropriate mixture of extraction solvent (8.0 microL C2Cl4) and disperser solvent (1.00 mL acetone) are injected into the aqueous sample (5.00 mL) by syringe, rapidly. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. After centrifuging, the fine particles of extraction solvent are sedimented in the bottom of the conical test tube (5.0 +/- 0.2 microL). The performance of DLLME is illustrated with the determination of polycyclic aromatic hydrocarbons (PAHs) in water samples by using gas chromatography-flame ionization detection (GC-FID). Some important parameters, such as kind of extraction and disperser solvent and volume of them, and extraction time were investigated. Under the optimum conditions the enrichment factor ranged from 603 to 1113 and the recovery ranged from 60.3 to 111.3%. The linear range was 0.02-200 microg/L (four orders of magnitude) and limit of detection was 0.007-0.030 microg/L for most of analytes. The relative standard deviations (RSDs) for 2 microg/L of PAHs in water by using internal standard were in the range 1.4-10.2% (n = 5). The recoveries of PAHs from surface water at spiking level of 5.0 microg/L were 82.0-111.0%. The ability of DLLME technique in the extraction of other organic compounds such as organochlorine pesticides, organophosphorus pesticides and substituted benzene compounds (benzene, toluene, ethyl benzene, and xylenes) from water samples were studied. The advantages of DLLME method are simplicity of operation, rapidity, low cost, high recovery, and enrichment factor.     

Simultaneous derivatization and extraction of anilines in waste water with dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometric detection

The one-step derivatization and extraction technique for the determination of anilines in river water by dispersive liquid-liquid microextraction (DLLME) is presented. In this method the anilines are extracted by DLLME and derivatized with pentafluorobenzaldehyde (PFBAY) in aqueous solution simultaneously. In this derivatization/extraction method, 0.5 ml acetone (disperser solvent) containing 10 microl chlorobenzene (extraction solvent) and 30 g/l pentafluorobenzaldehyde (PFBAY) dissolved in methanol was rapidly injected by syringe into 5 ml aqueous sample (pH 4.6). Within 20 min the analytes extracted and derivatized were almost finished. After centrifugation, 2 microl sedimented phase containing enriched analytes was determined by GC-MS. The effects of extraction and disperser solvent type and their volume, pH value of sample solution, derivatization and extraction time, derivatization and extraction temperature were investigated. Linearity in this developed method was ranging from 0.25 to 70 microg/l, and the correlation coefficients (R2) were between 0.9955 and 0.9989, and reasonable reproducibility ranging from 5.8 to 11.8% (n=5). Method detection limits (MDLs) ranged from 0.04 to 0.09 microg/l (n=5).     

Rapid determination of lead in water samples by dispersive liquid-liquid microextraction coupled with electrothermal atomic absorption spectrometry

The need for highly reliable methods for the determination of trace and ultratrace elements has been recognized in analytical chemistry and environmental science. A simple and powerful microextraction technique was used for the detection of the lead ultratrace amounts in water samples using the dispersive liquid-liquid microextraction (DLLME), followed by the electrothermal atomic absorption spectrometry (ET AAS). In this microextraction technique, a mixture of 0.50 mL acetone (disperser solvent), containing 35 microL carbon tetrachloride (extraction solvent) and 5 microL diethyldithiophosphoric acid (chelating agent), was rapidly injected by syringe into the 5.00 mL water sample, spiked with lead. In this process, the lead ions reacted with the chelating agent and were extracted into the fine droplets of CCl(4). After centrifugation (2 min at 5000 rpm), the fine CCl4 droplets were sedimented at the bottom of the conical test tube (25+/-1 microL). Then, 20 microL from the sedimented phase, containing the enriched analyte, was determined by ET AAS. The next step was the optimization of various experimental conditions, affecting DLLME, such as the type and the volume of the extraction solvent, the type and the volume of the disperser solvent, the extraction time, the salt effect, pH and the chelating agent amount. Moreover, the effect of the interfering ions on the analytes recovery was also investigated. Under the optimum conditions, the enrichment factor of 150 was obtained from only a 5.00 mL water sample. The calibration graph was linear in the range of 0.05-1 microg L(-1) with the detection limit of 0.02 microg L(-1). The relative standard deviation (R.S.D.) for seven replicate measurements of 0.50 microg L(-1) of lead was 2.5%. The relative lead recoveries in mineral, tap, well and sea water samples at the spiking level of 0.20 and 0.40 microg L(-1) varied from 93.5 to 105.0. The characteristics of the proposed method were compared with the cloud point extraction (CPE), the liquid-liquid extraction, the solid phase extraction (SPE), the on-line solid phase extraction (SPE) and the co-precipitation, based on bibliographic data. The main DLLME advantages combined with ET AAS were simplicity of operation, rapidity, low cost, high-enrichment factor, good repeatability, low consumption of extraction solvent, requiring a low sample volume (5.00 mL).     

Determination of some organophosphorus and azole group pesticides in water samples by dispersive liquid-liquid microextraction coupled with GC/MS

A dispersive liquid-liquid microextraction (DLLME) procedure coupled with GC/MS detection is described for preconcentration and determination of some organophosphorus and azole group pesticides from water samples. Experimental conditions affecting the DLLME procedure were optimized by means of an experimental design. A mixture of 60 microL chlorobenzene (extraction solvent) and 750 microL acetonitrile (disperser solvent), 3.5 min extraction time, and 7.5 mL aqueous sample volume were chosen for the best recovery by DLLME. The linear range was 1.6-32 microg/L. The LOD ranged from 48.8 to 68.7 ng/L. The RSD values for organophosphorus and azole group pesticides at spiking levels of 3, 6, and 9 microg/L in water samples were in the range of 1.1-12.8%. The applicability and accuracy of the developed method were determined by analysis of spiked water samples, and the recoveries of the analyzed pesticides from artesian, stream, and tap waters at spiking levels of 3, 6, and 9 microg/L were 89.3-105.6, 89.5-103.0, and 92.0-111.3%, respectively.     

Evaluation of dispersive liquid-liquid microextraction for the simultaneous determination of chlorophenols and haloanisoles in wines and cork stoppers using gas chromatography-mass spectrometry

Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) was evaluated for the simultaneous determination of five chlorophenols and seven haloanisoles in wines and cork stoppers. Parameters, such as the nature and volume of the extracting and disperser solvents, extraction time, salt addition, centrifugation time and sample volume or mass, affecting the DLLME were carefully optimized to extract and preconcentrate chlorophenols, in the form of their acetylated derivatives, and haloanisoles. In this extraction method, 1mL of acetone (disperser solvent) containing 30μL of carbon tetrachloride (extraction solvent) was rapidly injected by a syringe into 5mL of sample solution containing 200μL of acetic anhydride (derivatizing reagent) and 0.5mL of phosphate buffer solution, thereby forming a cloudy solution. After extraction, phase separation was performed by centrifugation, and a volume of 4μL of the sedimented phase was analyzed by GC-MS. The wine samples were directly used for the DLLME extraction (red wines required a 1:1 dilution with water). For cork samples, the target analytes were first extracted with pentane, the solvent was evaporated and the residue reconstituted with acetone before DLLME. The use of an internal standard (2,4-dibromoanisole) notably improved the repeatability of the procedure. Under the optimized conditions, detection limits ranged from 0.004 to 0.108ngmL(-1) in wine samples (24-220pgg(-1) in corks), depending on the compound and the sample analyzed. The enrichment factors for haloanisoles were in the 380-700-fold range.     

Determination of atranol and chloroatranol in perfumes using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A new analytical method based on simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS), for the determination of the allergenic compounds atranol and chloroatranol in perfumes, is presented. Derivatization of the target analytes by means of acetylation with anhydride acetic in carbonate buffer was carried out. Thereby volatility and detectability were increased for improved GC–MS sensitivity. In addition, extractability by DLLME was also enhanced due to a less polar character of the solutes. A liquid–liquid extraction was performed before DLLME to clean up the sample and to obtain an aqueous sample solution, free of the low polar matrix from the essential oils, as donor phase. Different parameters, such as the nature and volume of both the extraction and disperser solvents, the ionic strength of the aqueous donor phase or the effect of the derivatization reagent volume, were optimized. Under the selected conditions (injection of a mixture of 750 μL of acetone as disperser solvent, 100 μL of chloroform as extraction solvent and 100 μL of anhydride acetic as derivatization reagent) the figures of merit of the proposed method were evaluated. Limits of detection in the low ng mL⁻¹ range were obtained. Matrix effect was observed in real perfume samples and thus, standard addition calibration is recommended.     

Automated analysis of 2-methyl-3-furanthiol and 3-mercaptohexyl acetate at ng L(-1) level by headspace solid-phase microextracion with on-fibre derivatisation and gas chromatography-negative chemical ionization mass spectrometric determination

A new method was used for the extraction of organophosphorus pesticides (OPPs) from water samples: dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-flame photometric detection (GC-FPD). In this extraction method, a mixture of 12.0 microL chlorobenzene (extraction solvent) and 1.00 mL acetone (disperser solvent) is rapidly injected into the 5.00 mL water sample by syringe. Thereby, a cloudy solution is formed. In fact, the cloudy state is because of the formation of fine droplets of chlorobenzene, which has been dispersed among the sample solution. In this step, the OPPs in water sample are extracted into the fine droplets of chlorobenzene. After centrifuging (2 min at 5000 rpm), the fine droplets of chlorobenzene are sedimented in the bottom of the conical test tube (5.0+/-0.3 microL). Sedimented phase (0.50 microl) is injected into the GC for separation and determination of OPPs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, temperature and salt effect were investigated. Under the optimum conditions, the enrichment factors and extraction recoveries were high and ranged between 789-1070 and 78.9-107%, respectively. The linear range was wide (10-100,000 pg/mL, four orders of magnitude) and limit of detections were very low and were between 3 to 20 pg/mL for most of the analytes. The relative standard deviations (RSDs) for 2.00 microg/L of OPPs in water with internal standard were in the range of 1.2-5.6% (n=5) and without internal standard were in the range of 4.6-6.5%. The relative recoveries of OPPs from river, well and farm water at spiking levels of 50, 500 and 5000 pg/mL were 84-125, 88-123 and 93-118%, respectively. The performance of proposed method was compared with solid-phase microextraction (SPME) and single drop microextraction. DLLME is a very simple and rapid (less than 3 min) method, which requires low volume of sample (5 mL). It also has high enrichment factor and recoveries for extraction of OPPs from water.     

Dispersive Liquid-Liquid Microextraction Coupled to Gas Chromatography-Electron Capture Detection for the Analysis of Trihalomethane Formation Potential

Dispersive liquid-liquid microextraction (DLLME) is an attractive miniaturized technique that utilizes microliter volumes of extraction solvents. In this study, a DLLME technique was employed for the determination of four major trihalomethane (THM) compounds and analyzed using gas chromatography-electron capture detection. Optimization was conducted in terms of type and volume of disperser solvent, type and volume of extraction solvent, and addition of salt and extraction time. Optimized conditions employed methanol (0.25 mL) as the disperser solvent containing carbon disulfide (20 µL) as the extraction solvent. The linear range was 0.020–4.00 µg/L. Low limits of detection for the analytes were obtained in the range of 0.01 to 0.24 µg/L with enrichment factors ranging from 95–283. The relative recoveries of THMs from water samples at spiking level of 2 µg/L were in the range of 79.9 to 103.4%. This method was successfully applied to the determination of THM formation potential (THMFP) in river water samples. It was found that the concentration of THMFP in three Malaysian rivers were below the maximum permissible limits of World Health Organization (WHO).     

Ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and derivatization of sulfonamides in river water, honey, milk, and animal plasma

The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples.     

Dispersion‐solidification liquid–liquid microextraction for volatile aromatic hydrocarbons determination: Comparison with liquid phase microextraction based on the solidification of a floating drop

Two microextraction techniques – liquid phase microextraction based on solidification of a floating organic drop (LPME‐SFO) and dispersive liquid–liquid microextraction combined with a solidification of a floating organic drop (DLLME‐SFO) – are explored for benzene, toluene, ethylbenzene and o‐xylene sampling and preconcentration. The investigation covers the effects of extraction solvent type, extraction and disperser solvents' volume, and the extraction time. For both techniques 1‐undecanol containing n‐heptane as internal standard was used as an extracting solvent. For DLLME‐SFO acetone was used as a disperser solvent. The calibration curves for both techniques and for all the analytes were linear up to 10 μg/mL, correlation coefficients were in the range 0.997–0.998, enrichment factors were from 87 for benzene to 290 for o‐xylene, detection limits were from 0.31 and 0.35 μg/L for benzene to 0.15 and 0.10 μg/L for o‐xylene for LPME‐SFO and DLLME‐SFO, respectively. Repeatabilities of the results were acceptable with RSDs up to 12%. Being comparable with LPME‐SFO in the analytical characteristics, DLLME‐SFO is superior to LPME‐SFO in the extraction time. A possibility to apply the proposed techniques for volatile aromatic hydrocarbons determination in tap water and snow was demonstrated.     

Development of dispersive liquid-liquid microextraction combined with gas chromatography-mass spectrometry as a simple, rapid and highly sensitive method for the determination of phthalate esters in water samples

A simple, rapid and efficient method, the dispersive liquid-liquid microextraction (DLLME) in conjunction with gas chromatography-mass spectrometry (GC-MS), has been developed for the extraction and determination of phthalate esters (dimethyl phthalate, diallyl phthalate, di-n-butyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate and di-2-ethylhexyl phthalate) in water samples. Factors relevant to the microextraction efficiency, such as the kind of extraction, the disperser solvent and their volume, the salt effect and the extraction time were investigated and optimized. Under the optimized extraction conditions (extraction solvent: chlorobenzene, volume, 9.5microL; disperser solvent: acetone, volume, 0.50mL, without salt addition and extraction time below 5s), the figures of merit of the proposed method were evaluated. The values of the detection limit of the method were in the range of 0.002-0.008microgL(-1), while the RSD% value for the analysis of 1microgL(-1) of the analytes was below 6.8% (n=4). A good linearity (0.9962>/=r(2)>/=0.9901) and a broad linear range (0.02-100microgL(-1)) were obtained. The method exhibited enrichment factors and recoveries, ranging from 681 to 889 and 68.1 to 88.9%, respectively, at room temperature (25+/-1 degrees C). Finally, the proposed method was successfully utilized for the preconcentration and determination of the phthalate esters in different real water samples and satisfactory results were obtained.     

Use of dispersive liquid-liquid microextraction for simultaneous preconcentration of samarium,europium, gadolinium and dysprosium

A new preconcetration method of dispersive liquid-liquid microextraction (DLLME) was developed for simultaneous preconcentration of samarium, europium, gadolinium and dysprosium. DLLME technique was successfully used as a sample preparation method. In this preconcentration method, an appropriate mixture of extraction solvent, disperser solvent was injected rapidly into an aqueous solution containing Sm, Eu, Gd and Dy after complex formation using chelating reagent of the 1-(2-pyridylazo)-2-naphthol (PAN). After phase separation, 0.5 mL of the settled phase containing enriched analytes was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The main factors affected the preconcentration of Sm, Eu, Gd and Dy were extraction and dispersive solvent type and their volume, extraction time, volume of chelating agent (PAN), centrifuge speed and drying temperature of the samples. Under the best operating condition simultaneous preconcentration factors of 80, 100, 103 and 78 were obtained for Sm, Eu, Gd and Dy, respectively.     

Determination of hydroxylated benzophenone UV filters in sea water samples by dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A new analytical method for the determination of four hydroxylated benzophenone UV filters (i.e. 2-hydroxy-4-methoxybenzophenone (HMB), 2,4-dihydroxybenzophenone (DHB), 2,2′-dihydroxy-4-methoxybenzophenone (DHMB) and 2,3,4-trihydroxybenzophenone (THB)) in sea water samples is presented. The method is based on dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS) determination. The variables involved in the DLLME process were studied. Under optimized conditions, 1000 μL of acetone (disperser solvent) containing 60 μL of chloroform (extraction solvent) were injected into 5 mL of aqueous sample adjusted to pH 4 and containing 10% NaCl. Before injecting into the GC–MS system, the DLLME extracts were evaporated under an air stream and then reconstituted with N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA), thus allowing the target analytes to be converted into their trimethylsilyl derivatives. The best conditions for the derivatization reaction were 75 °C and 30 min. High enrichment factors for all the target analytes (ranging from 58 to 64) and good repeatability (RSD around 6%) were obtained. The limits of detection were in the range of 32–50 ng L⁻¹, depending on the analyte. The recoveries obtained by using the proposed DLLME–GC–MS method evidenced the presence of matrix effects for some of the target analytes, and thereby the standard addition calibration method was employed. Finally, the validated method was applied to the analysis of sea water samples.     

Determination of four aromatic amines in water samples using dispersive liquid-liquid microextraction combined with HPLC

A new method for the determination of four aromatic amines in water samples was developed by using dispersive liquid-liquid microextraction (DLLME) technique combined with HPLC-variable wavelength detection (HPLC-VWD). In this extraction method, 0.50 mL methanol (as dispersive solvent) containing 25.0 microL tetrachloroethane (as extraction solvent) was rapidly injected by a syringe into 5.00 mL water sample. Accordingly, a cloudy solution was formed. After centrifugation for 2 min at 4000 rpm, the fine droplets of the tetrachloroethane containing the analytes were sedimented in the bottom of the conical test tube (7+/-0.2 microL). Then, 5.0 microL of the settled phase was determined by HPLC-VWD. Parameters such as the kind and volume of extraction solvent and dispersive solvent, extraction time, and salt concentration were optimized. Under the optimum conditions, the enrichment factors ranged from 41.3 to 94.5. Linearity was observed in the range of 5-5000 ng/mL. The LODs based on S/N of 3 ranged from 0.8 to 1.8 ng/mL. The RSDs (for 400 ng/mL of p-toluidine and o-chloroaniline, 100 ng/mL of p-chloroaniline and p-bromoaniline) varied from 4.1 to 5.3% (n=6). The water samples collected from rivers and lakes were successfully analyzed by the proposed method and the relative recoveries were in the range of 85.4-111.7% and 90.2-101.3%, respectively.     

Determination of Trihalomethanes in Drinking Water by Dispersive Liquid–Liquid Microextraction then Gas Chromatography with Electron-Capture Detection

Dispersive liquid–liquid microextraction (DLLME) has been used for preconcentration of trihalomethanes (THMs) in drinking water. In DLLME an appropriate mixture of an extraction solvent (20.0 μL carbon disulfide) and a disperser solvent (0.50 mL acetone) was used to form a cloudy solution from a 5.00-mL aqueous sample containing the analytes. After phase separation by centrifugation the enriched analytes in the settled phase (6.5 ± 0.3 μL) were determined by gas chromatography with electron-capture detection (GC–ECD). Different experimental conditions, for example type and volume of extraction solvent, type and volume of disperser solvent, extraction time, and use of salt, were investigated. After optimization of the conditions the enrichment factor ranged from 116 to 355 and the limit of detection from 0.005 to 0.040 μg L⁻¹. The linear range was 0.01–50 μg L⁻¹ (more than three orders of magnitude). Relative standard deviations (RSDs) for 2.00 μg L⁻¹ THMs in water, with internal standard, were in the range 1.3–5.9% (n = 5); without internal standard they were in the range 3.7–8.6% (n = 5). The method was successfully used for extraction and determination of THMs in drinking water. The results showed that total concentrations of THMs in drinking water from two areas of Tehran, Iran, were approximately 10.9 and 14.1 μg L⁻¹. Relative recoveries from samples of drinking water spiked at levels of 2.00 and 5.00 μg L⁻¹ were 95.0–107.8 and 92.2–100.9%, respectively. Comparison of this method with other methods indicates DLLME is a very simple and rapid (less than 2 min) method which requires a small volume of sample (5 mL).     

Tandem use of solid-phase extraction and dispersive liquid-liquid microextraction for the determination of mononitrotoluenes in aquatic environment

Solid‐phase extraction (SPE) in tandem with dispersive liquid–liquid microextraction (DLLME) has been developed for the determination of mononitrotoluenes (MNTs) in several aquatic samples using gas chromatography‐flame ionization (GC‐FID) detection system. In the hyphenated SPE‐DLLME, initially MNTs were extracted from a large volume of aqueous samples (100 mL) into a 500‐mg octadecyl silane (C₁₈) sorbent. After the elution of analytes from the sorbent with acetonitrile, the obtained solution was put under the DLLME procedure, so that the extra preconcentration factors could be achieved. The parameters influencing the extraction efficiency such as breakthrough volume, type and volume of the elution solvent (disperser solvent) and extracting solvent, as well as the salt addition, were studied and optimized. The calibration curves were linear in the range of 0.5–500 μg/L and the limit of detection for all analytes was found to be 0.2 μg/L. The relative standard deviations (for 0.75 μg/L of MNTs) without internal standard varied from 2.0 to 6.4% (n=5). The relative recoveries of the well, river and sea water samples, spiked at the concentration level of 0.75 μg/L of the analytes, were in the range of 85–118%.     

Determination of volatile phenols in red wines by dispersive liquid-liquid microextraction and gas chromatography-mass spectrometry detection

A new method was developed for analysing 4-ethylguaiacol and 4-ethylphenol in the aroma of red wines using dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry detection (GC-MS). Parameters such as extraction solvent, sample volume and disperser solvent were studied and optimised to obtain the best extraction results with the minimum interference from other substances, thus giving clean chromatograms. The response linearity was studied in the usual concentration ranges of analytes in wines (50-1500 microg/L). Repeatability and reproducibility of this method were lower than 5% for both volatile phenols. Limits of detection and limits of quantification were also determined, and the values found were 28 and 95 microg/L for 4-ethylguaiacol and 44 and 147 microg/L for 4-ethylphenol, respectively. This new method has been used for the determination of the volatile phenols concentration in different samples of Tannat wine affected by Brettanomyces contamination.     

Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of three carbamate pesticides in water samples

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography (HPLC), has been developed for the determination of three carbamate pesticides (methomyl, carbofuran and carbaryl) in water samples. In this extraction process, a mixture of 35 µL chlorobenzene (extraction solvent) and 1.0 mL acetonitrile (disperser solvent) was rapidly injected into the 5.0 mL aqueous sample containing the analytes. After centrifuging (5 min at 4000 rpm), the fine droplets of chlorobenzene were sedimented in the bottom of the conical test tube. Sedimented phase (20 µL) was injected into the HPLC for analysis. Some important parameters, such as kind and volume of extraction and disperser solvent, extraction time and salt addition were investigated and optimised. Under the optimum extraction condition, the enrichment factors and extraction recoveries ranged from 148% to 189% and 74.2% to 94.4%, respectively. The methods yielded a linear range in the concentration from 1 to 1000 µg L^?1 for carbofuran and carbaryl, 5 to 1000 µg L^?1 for methomyl, and the limits of detection were 0.5, 0.9 and 0.1 µg L^?1, respectively. The relative standard deviations (RSD) for the extraction of 500 µg L^?1 carbamate pesticides were in the range of 1.8–4.6% (n = 6). This method could be successfully applied for the determination of carbamate pesticides in tap water, river water and rain water.     

Development of a simultaneous liquid-liquid extraction and chiral derivatization method for stereospecific GC-MS analysis of amphetamine-type stimulants in human urine using fractional factorial design

A stereospecific gas chromatography-mass spectrometry analysis method for amphetamine-type stimulants in human urine was recently developed. For maximum efficiency, liquid-liquid extraction and chiral derivatization of the analytes using (R)-(-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride were performed simultaneously. The effects of (1) use of saturated sodium chloride in 2.0 m sodium hydroxide, (2) extraction solvent volume, (3) percentage of triethylamine, (4) derivatization reagent volume, (5) sample mixing time, (6) incubation temperature and (7) incubation time on method sensitivity and variability were assessed using a two-level, eight-run Plackett-Burman design followed by a fold-over design. The use of saturated sodium chloride solution and the derivatization reagent volume were significant factors (ANOVA, p < 0.01). The saturated sodium chloride solution decreased sensitivity whereas an increased volume of derivatization reagent increased sensitivity. Calibration curves for all analytes were linear between 5 and 500 microg/L, with correlation coefficients of >0.99. Detection limits were 相似文献