Quantitation of antioxidants in water samples using ionic liquid dispersive liquid-liquid microextraction followed by high-performance liquid chromatography-ultraviolet detection

A simple and efficient method, ionic liquid-based dispersive liquid-liquid microextraction combined with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), has been applied for the extraction and determination of some antioxidants (Irganox 1010, Irganox 1076 and Irgafos 168) in water samples. The microextraction efficiency factors were investigated and optimized: 1-hexyl-3-methylimidazolium hexafluorophosphate [C(6)MIM][PF(6)] (0.06 g) as extracting solvent, methanol (0.5 mL) as disperser solvent without salt addition. Under the selected conditions, enrichment factors up to 48-fold, limits of detection (LODs) of 5.0-10.0 ng/mL and dynamic linear ranges of 25-1500 ng/mL were obtained. A reasonable repeatability (RSD≤11.8%, n=5) with satisfactory linearity (r(2)≥0.9954) of the results illustrated a good performance of the presented method. The accuracy of the method was tested by the relative recovery experiments on spiked samples, with results ranging from 85 to 118%. Finally, the method was successfully applied for determination of the analytes in several real water samples.     

Ionic liquid-based dispersive liquid-liquid microextraction for sensitive determination of aromatic amines in environmental water

Ionic liquid-based dispersive liquid-liquid microextraction was developed for the extraction and preconcentration of aromatic amine from environmental water. A suitable mixture of extraction solvent (100 μL, 1-butyl-3-methylimidazolium hexafluorophoshate) and dispersive solvent (750 μL, methanol) were injected into the aqueous samples (10.00 mL), forming a cloudy solution. After centrifuging, enriched analytes in the sediment phase were determined by HPLC-UV. The effect of various factors, such as the extraction and dispersive solvent, sample pH, extraction time and salt effect were investigated. Under optimum conditions, enrichment factors for 2-anilinoethanol, o-chloroaniline and 4-bromo-N,N-dimethylaniline were above 50 and the limits of detection (LODs) were 0.023, 0.015 and 0.026 ng/mL, respectively. Their linear ranges were 0.8-400 ng/mL for 2-anilinoethanol, 0.5-200 ng/mL for o-chloroaniline and 0.4-200 ng/mL for 4-bromo-N,N-dimethylaniline, respectively. Relative standard deviations (RSDs) were below 5.0%. The relative recoveries from samples of environmental water were in the range of 82.0-94.0%. Compared with other methods, dispersive liquid-liquid microextraction is simple, rapid, sensitive and economical.     

Determination of insecticides in water using in situ halide exchange reaction-assisted ionic liquid dispersive liquid-liquid microextraction followed by high-performance liquid chromatography

A dispersive liquid-liquid microextraction (DLLME) method using in situ halide exchange reaction to form ionic liquid (IL) extraction phase was developed to determine four insecticides (i.e. methoxyfenozide, tetrachlorvinphos, thiamethoxam, and diafenthiuron) in water samples. The preconcentration procedure, followed by high-performance liquid chromatography and variable wavelength detectors (VWD), enabled the formation of the immiscible IL extraction phase; the insecticides were transferred into the IL phase simultaneously, which enhanced the efficiency and sufficiency, greatly shortening the operation time. The experimental parameters affecting the extraction efficiency including volume of extraction IL, extraction and centrifugation times, volume of the sample solution and exchanging reagent, and addition of organic solvent and salt were investigated and optimized. Under optimized conditions, the extractions yielded recoveries of the target analytes from 82 to 102%. The calibration curves were linear, and the correlation coefficient ranged from 0.9990 to 0.9999 under the concentration levels of 5-200 μg/L. The relative standard deviation (n=6) was 2.9-4.6%. The limits of detection (LODs) for the four insecticides were between 0.98 and 2.54 μg/L.     

Application of dispersive liquid-liquid microextraction combined with high-performance liquid chromatography for the determination of methomyl in natural waters

A new method was developed for determination of methomyl in water samples by combining a dispersive liquid-liquid microextraction (DLLME) technique with HPLC-variable wavelength detection (VWD). In this extraction method, 0.50 mL of methanol (as dispersive solvent) containing 20.0 microL of tetrachloroethane (as extraction solvent) was rapidly injected by syringe into a 5.00-mL water sample containing the analyte, thereby forming a cloudy solution. After phase separation by centrifugation for 2 min at 4000 rpm, the enriched analyte in the settled phase (8 +/- 0.2 microL) was at the bottom of the conical test tube. A 5.0-microL volume of the settled phase was analyzed by HPLC-VWD. Parameters such as the nature and volume of the extraction solvent and the dispersive solvent, extraction time, and the salt concentration were optimized. Under the optimum conditions, the enrichment factor could reach 70.7 for a 5.00-mL water sample and the linear range, detection limit (S/N = 3), and precision (RSD, n = 6) were 3-5000 ng/mL, 1.0 ng/mL, and 2.6%, respectively. River and lake water samples were successfully analyzed by the proposed method. Comparison of this method with solid-phase extraction, solid-phase microextraction, and single-drop microextraction, indicates that DLLME combined with HPLC-VWD is a simple, fast, and low-cost method for the determination of methomyl, and thus has tremendous potential in trace analysis of methomyl in natural waters.     

Validated dispersive liquid-liquid microextraction for analysis of organophosphorous pesticides in water

Dispersive liquid-liquid microextraction (DLLME) combined with gas chromatography and mass spectrometry (GC-MS) was applied to the determination of six organophosphorous pesticides (OPPs) in water samples. The analytes included in this study were prophos, diazinon, chlorpyrifos methyl, methyl parathion, fenchlorphos and chlorpyrifos. Several extraction and dispersion solvents were tested for dispersive liquid-liquid microextraction of these analytes and the best results were obtained using chloroform as extraction solvent and 2-propanol as dispersion solvent. Calibration curves of the analytes in water samples were constructed in the concentration range from 100 to 1100 ng/L for prophos, diazinon and methyl parathion and in the range from 100 to 1000 ng/L for chlorpyrifos methyl, fenchlorphos and chlorpyrifos. Limits of detection (LODs) were in the range of 1.5-9.1 ng/L and limits of quantification (LOQs) were in the range of 5.1-30.3 ng/L, below the maximum admissible level for drinking water. Relative standard deviations (RSDs) were between 6.5 and 10.1% in the concentration range of 100-1000 ng/L. The relative recoveries (%RRs) of tap, well and irrigation water samples fortified at 800 ng/L were in the range of 46.1-129.4%, with a larger matrix effect being detected in tap water.     

Simultaneous determination of tetrahydropalmatine and tetrahydroberberine in rat urine using dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography

Dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied in rat urine for the extraction and determination of tetrahydropalmatine (THP) and tetrahydroberberine (THB), both active components in Rhizoma corydalis. Various parameters affecting the extraction efficiency, such as the type and volume of extraction and dispersive solvent, pH, etc. were evaluated. Under the optimal conditions (extraction solvent: 37 μL of chloroform, dispersive solvent: 100 μL of methanol, alkaline with 100 μL of 1 mol/L NaOH, and without salt addition), the enrichment factors of THP and THB were more than 30. The extraction recoveries were 69.8-75.8% and 72.7-77.6% for THP and THB in rat urine, respectively. Both THP and THB showed good linearity in the range of 0.025-2.5 μg/mL, and the limit of quantification was 0.025 μg/mL (S/N=10, n=6). The intra-day and inter-day precision of THP and THB were <12.6%. The relative recoveries ranged from 95.5 to 107.4% and 96.8 to 100.9% for THP and THB in rat urine, respectively. The method has been successfully applied to rat urine samples. The results demonstrated that DLLME is a very simple, rapid and efficient method for the extraction and preconcentration of THP and THB from urine samples.     

Using dispersive liquid-liquid microextraction and liquid chromatography for determination of guaifenesin enantiomers in human urine

A simple, rapid, and efficient method, dispersive liquid–liquid microextraction (DLLME) coupled with high‐performance liquid chromatography‐fluorescence detector, has been developed for the determination of guaifenesin (GUA) enantiomers in human urine samples after an oral dose administration of its syrup formulation. Urine samples were collected during the time intervals 0–2, 2–4, and 4–6 h and concentration and ratio of two enantiomers was determined. The ratio of R‐(?) to S‐(+) enantiomer concentrations in urine showed an increase with time, with R/S ratios of 0.66 at 2 h and 2.23 at 6 h. For microextraction process, a mixture of extraction solvent (dichloromethane, 100 μL) and dispersive solvent (THF, 1 mL) was rapidly injected into 5.0 mL diluted urine sample for the formation of cloudy solution and extraction of enantiomers into the fine droplets of CH₂Cl₂. After optimization of HPLC enantioselective conditions, some important parameters, such as the kind and volume of extraction and dispersive solvents, extraction time, temperature, pH, and salt effect were optimized for dispersive liquid–liquid microextraction process. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 10 to 2000 ng/mL for target analytes. LOD was 3.00 ng/mL for both of the enantiomers.     

Ionic liquid/ionic liquid dispersive liquid-liquid microextraction

In this article, a novel and simple microextraction method, termed ionic liquid/ionic liquid dispersive liquid–liquid microextraction (IL/IL‐DLLME), has been designed and developed for the rapid enrichment and analysis of environmental pollutants. Instead of using hazardous organic solvents, two kinds of ILs, hydrophobic IL and hydrophilic IL, were used as extraction solvent and disperser solvent in IL/IL‐DLLME step, respectively. Permethrin and biphenthrin, two of the often‐used pyrethroid pesticides, were used as model compounds. Factors that may affect the enrichment efficiencies were investigated and optimized in detail. Under optimum conditions, permethrin and biphenthrin exhibited a wide linear relationship over the range 1–100 μg/L. For permethrin and biphenthrin, the precisions were 4.65–7.78%, and limits of detection were found to be 0.28 and 0.83 μg/L, respectively. Satisfactory results were achieved when the present method was applied to analyze the target compounds in real‐world water samples with spiked recoveries over the range 84.1–113.5%. All these facts indicated that IL/IL‐DLLME is a simple and rapid alternative for the enrichment and analysis of environmental pollutants and will have a wide application perspective in the future.     

Improved solvent collection system for a dispersive liquid-liquid microextraction of organochlorine pesticides from water using low-density organic solvent

In this study, the organochlorine pesticides (OCPs) levels in lake and tap water samples were determined by a dispersive liquid-liquid microextraction method using a low-density organic solvent and an improved solvent collection system (DLLME-ISCS). This method used a very small volume of a solvent of low toxicity (11 μL of 1-nonanol and 400 μL of methanol) to extract OCPs from 10 mL water samples prior to the analysis by GC. After centrifugation in the dispersive liquid-liquid microextraction, there was a liquid organic drop floating between the water surface and the glass wall of the centrifuge tube. The liquid organic drop (with some water phase) was transferred into a microtube (3 mm×15 mm) with a syringe. The organic and aqueous phases were separated in the microtube immediately. Then, 1 μL of the organic solvent (which was in the upper portion of liquid in the microtube) was easily collected by a syringe and injected into the GC-ECD system for the analysis. Under optimum conditions, the linear range of this method was 5-5000 ng/L for most of the analytes. The correlation coefficient was higher than 0.997. Enrichment factors ranged from 1309 to 3629. The relative recoveries ranged from 73 to 119% for lake water samples. The LODs of the method ranged from 0.7 to 9.4 ng/L. The precision of the method ranged from 1.0 to 10.8% for lake water.     

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.     

Simultaneous preconcentration and determination of 2,4‐D,alachlor and atrazine in aqueous samples using dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography ultraviolet detection

Dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography‐ultraviolet detection as a fast and inexpensive technique was applied to the simultaneous extraction and determination of traces of three common herbicides, 2,4‐D, alachlor and atrazine, in aqueous samples. The critical experimental parameters, including type of the extraction and disperser solvents as well as their volumes, sample pH, salt addition, extraction time and centrifuging time, and speed were investigated and optimized. Under the optimum conditions, the calibration graphs found to be linear in the range of 0.3–200 μg/L with limits of detection in the range of 0.05–0.1 μg/L. The relative standard deviations were in the range of 4.5–6.2% (n = 7). The relative recoveries of well, tap, and river water samples which have been spiked with different levels of herbicides were 92.0–107.0, 82.0–104.0, and 82.0–86.0%, respectively.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Application of dispersive liquid-liquid microextraction and high-performance liquid chromatography for the determination of three phthalate esters in water samples

A novel method, dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detector (HPLC-VWD), has been developed for the determination of three phthalate esters (dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-n-butyl phthalate (DnBP)) in water samples. A mixture of extraction solvent (41 μL carbon tetrachloride) and dispersive solvent (0.75 mL acetonitrile) were rapidly injected into 5.0 mL aqueous sample for the formation of cloudy solution, the analytes in the sample were extracted into the fine droplets of CCl₄. After extraction, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were determined by HPLC-VWD. Some important parameters, such as the kind and volume of extraction solvent and dispersive solvent, extraction time and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 5 to 5000 ng mL⁻¹ for target analytes. The enrichment factors for DMP, DEP and DnBP were 45, 92 and 196, respectively, and the limits of detection were 1.8, 0.88 and 0.64 ng mL⁻¹, respectively. The relative standard deviations (R.S.D.) for the extraction of 10 ng mL⁻¹ of phthalate esters were in the range of 4.3-5.9% (n = 7). Lake water, tap water and bottled mineral water samples were successfully analyzed using the proposed method.     

Novel method for the determination of five carbamate pesticides in water samples by dispersive liquid-liquid microextraction combined with high performance liquid chromatography

A novel method for the determination of five carbamate pesticides(metolcarb,carbofuran,carbaryl,isoprocard and diethofencard)in water samples was developed by dispersive liquid-liquid microextraction(DLLME)coupled with high performance liquid chromatography-diode array detector(HPLC-DAD).Some experimental parameters that influence the extraction efficiency were studied and optimized to obtain the best extraction results.Under the optimum conditions for the method,the calibration curve was linear in the c...     

Determination of the steroid hormone levels in water samples by dispersive liquid-liquid microextraction with solidification of a floating organic drop followed by high-performance liquid chromatography

In this study, the steroid hormone levels in river and tap water samples were determined by using a novel dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO). Several parameters were optimized, including the type and volume of the extraction and dispersive solvents, extraction time, and salt effect. DLLME-SFO is a fast, cheap, and easy-to-use method for detecting trace levels of samples. Most importantly, this method uses less-toxic solvent. The correlation coefficient of the calibration curve was higher than 0.9991. The linear range was from 5 to 1000 μg L⁻¹. The spiked environmental water samples were analyzed using DLLME-SFO. The relative recoveries ranged from 87% to 116% for river water (which was spiked with 4 μg L⁻¹ for E1, 3 μg L⁻¹ for E2, 4 μg L⁻¹ for EE2 and 9 μg L⁻¹ for E3) and 89% to 102% for tap water (which was spiked with 6 μg L⁻¹ for E1, 5 μg L⁻¹ for E2, 6 μg L⁻¹ for EE2 and 10 μg L⁻¹ for E3). The detection limits of the method ranged from 0.8 to 2.7 μg L⁻¹ for spiked river water and 1.4 to 3.1 μg L⁻¹ for spiked tap water. The methods precision ranged from 8% to 14% for spiked river water and 7% to 14% for spiked tap water.     

Determination of rifaximin in rat serum by ionic liquid based dispersive liquid-liquid microextraction combined with RP-HPLC

An efficient and environmental friendly ionic liquid based dispersive liquid-liquid microextraction procedure was optimized for determination of rifaximin in rat serum by reverse phase high-performance liquid chromatography. The effect of ionic liquids, dispersive solvents, extractant/disperser ratio, and salt concentrations on sample recovery and enrichment factors were studied. Among the five ionic liquids studied in the present investigation, 1-butyl-3-methylimidazolium hexafluorophosphate was found to be most effective for extraction of rifaximin. The recovery was found to be more than 98% using 1-butyl-3-methylimidazolium hexafluorophosphate and methanol as extraction and dispersive solvents, at an extractant/disperser ratio of 0.43. The recovery was further enhanced to 99.5% by the addition of 5.0% NaCl solution. A threefold enhancement in detection limit was achieved when compared to protein precipitation. The ionic liquid containing the extracted rifaximin was directly injected into HPLC system. The linear relationship was observed in the range of 0.03-10.0 μg/mL with the correlation coefficient (r(2) ) 0.9998. Limits of detection and quantification were found to be 0.01 and 0.03 μg/mL, respectively. The relative standard deviation was 2.5%. The method was validated and applied to study pharmacokinetics of rifaxmin in rat serum.     

Ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction for the separation and determination of estrogens in water samples by high‐performance liquid chromatography with fluorescence detection

An ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction method was proposed for the extraction and concentration of 17‐α‐estradiol, 17‐β‐estradiol‐benzoate, and quinestrol in environmental water samples by high‐performance liquid chromatography with fluorescence detection. 1‐Hexyl‐3‐methylimidazolium tetrafluoroborate was applied as foaming agent in the foam flotation process and dispersive solvent in microextraction. The introduction of the ion‐pairing and salting‐out agent NH₄PF₆ was beneficial to the improvement of recoveries for the hydrophobic ionic liquid phase and analytes. Parameters of the proposed method including concentration of 1‐hexyl‐3‐methylimidazolium tetrafluoroborate, flow rate of carrier gas, floatation time, types and concentration of ionic liquids, salt concentration in samples, extraction time, and centrifugation time were evaluated. The recoveries were between 98 and 105% with relative standard deviations lower than 7% for lake water and well water samples. The isolation of the target compounds from the water was found to be efficient, and the enrichment factors ranged from 4445 to 4632. This developing method is free of volatile organic solvents compared with regular extraction. Based on the unique properties of ionic liquids, the application of foam floatation, and dispersive liquid–liquid microextraction was widened.     

Part-per-trillion determination of chlorobenzenes in water using dispersive liquid-liquid microextraction combined gas chromatography-electron capture detection

In this study, a simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined gas chromatography-electron capture detection (GC-ECD), for the determination of chlorobenzenes (CBs) in water samples, has been described. This method involves the use of an appropriate mixture of extraction solvent (9.5 μl chlorobenzene) and disperser solvent (0.50 ml acetone) for the formation of cloudy solution in 5.00 ml aqueous sample containing analytes. After extraction, phase separation was performed by centrifugation and the enriched analytes in sedimented phase were determined by gas chromatography-electron capture detection (GC-ECD). Our simple conditions were conducted at room temperature with no stiring and no salt addition in order to minimize sample preparation steps. Parameters such as the kind and volume of extraction solvent, the kind and volume of disperser solvent, extraction time and salt effect, were studied and optimized. The method exhibited enrichment factors and recoveries ranging from 711 to 813 and 71.1 to 81.3%, respectively, within very short extraction time. The linearity of the method ranged from 0.05 to 100 μg l⁻¹ for dichlorobenzene isomers (DCB), 0.002-20 μg l⁻¹ for trichlorobenzene (TCB) and tetrachlorobenzene (TeCB) isomers and from 0.001 to 4 μg l⁻¹ for pentachlorobenzene (PeCB) and hexachlorobenzene (HCB). The limit of detection was in the low μg l⁻¹ level, ranging between 0.0005 and 0.05 μg l⁻¹. The relative standard deviations (R.S.D.s) for the concentration of DCB isomers, 5.00 μg l⁻¹, TCB and TeCB isomers, 0.500 μg l⁻¹, PeCB and HCB 0.100 μg l⁻¹ in water by using the internal standard were in the range of 0.52-2.8% (n = 5) and without the internal standard were in the range of 4.6-6.0% (n = 5). The relative recoveries of spiked CBs at different levels of chlorobenzene isomers in tap, well and river water samples were 109-121%, 105-113% and 87-120%, respectively. It is concluded that this method can be successfully applied for the determination of CBs in tap, river and well water samples.     

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%.     

Ultrasound-assisted emulsification microextraction for the determination of ephedrines in human urine by capillary electrophoresis with direct injection. Comparison with dispersive liquid-liquid microextraction

Ultrasound-assisted emulsification microextraction and dispersive liquid-liquid microextraction were compared for extraction of ephedrine, norephedrine, and pseudoephedrine from human urine samples prior to their determination by capillary electrophoresis. Formation of a microemulsion of the organic extract with an aqueous solution (at pH 3.2) containing 10% methanol facilitated the direct injection of the final extract into the capillary. Influential parameters affecting extraction efficiency were systematically studied and optimized. In order to enhance the sensitivity further, field-amplified sample injection was applied. Under optimum extraction and stacking conditions, enrichment factors of up to 140 and 1750 as compared to conventional capillary zone electrophoresis were obtained resulting in limits of detection of 12-33 μg/L and 1.0-2.8 μg/L with dispersive liquid-liquid microextraction and ultrasound-assisted emulsification microextraction when combined with field-amplified sample injection. Calibration graphs showed good linearity for urine samples by both methods with coefficients of determination higher than 0.9973 and percent relative standard deviations of the analyses in the range of 3.4-8.2% for (n = 5). The results showed that the use of ultrasound to assist microextraction provided higher extraction efficiencies than disperser solvents, regarding the hydrophilic nature of the investigated analytes.