Determination of Alkylphenols in Water by Dispersive Liquid–Liquid Microextraction Based on Solid Formation without a Disperser

Dispersive liquid–liquid microextraction based on solid formation without a disperser combined with high-performance liquid chromatography has been developed for the determination of 4-tert-butylphenol, 4-n-nonylphenol, and 4-tert-octylphenol. This method is rapid, easy, and uses only 10 µL of a low toxicity organic solvent (1-hexadecanethiol) for the extraction solvent and no disperser solvent. The extraction time and centrifugation time require less than 10 min. The linear range was 1–500 ng mL^?1 for 4-tert-butylphenol, 2–1000 ng mL^?1 for 4-tert-octylphenol, and 5–500 ng mL^?1 for 4-n-nonylphenol with r² ≥ 0.9986. The detection limits were between 0.2 and 1.5 ng mL^?1. The recoveries of lake and river water samples were in the range of 79% to 108%, and the relative standard deviations were 5% to 10%.     

LC Determination of Chloramphenicol in Honey Using Dispersive Liquid–Liquid Microextraction

A novel method, dispersive liquid–liquid microextraction coupled with liquid chromatography-variable wavelength detector (LC-VWD), has been developed for the determination of chloramphenicol (CAP) in honey. A mixture of extraction solvent (30 μL 1,1,2,2-tetrachloroethane) and dispersive solvent (1.00 mL acetonitrile) were rapidly injected by syringe into a 5.0 mL real sample for the formation of cloudy solution, the analyte in the sample was extracted into the fine droplets of C₂H₂Cl₄. After extraction, phase separation was performed by centrifugation and the enriched analyte in the sedimented phase was determined by LC-VWD. Some important parameters, such as the kind and volume of extraction solvent and dispersive solvent, extraction time, sample solution pH, sample volume and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 3 to 2,000 μg kg^?1 for target analyte. The enrichment factor for CAP was 68.2, and the limit of detection (S/N = 3) were 0.6 μg kg^?1. The relative standard deviation (RSD) for the extraction of 10 μg kg^?1 of CAP was 4.3% (n = 6). The main advantages of method are high speed, high enrichment factor, high recovery, good repeatability and extraction solvent volume at μL level. Honey samples were successfully analyzed using the proposed method.     

Determination of Tetracyclines in Milk,Eggs and Honey Using in-situ Ionic Liquid Based Dispersive Liquid–Liquid Microextraction

In this study, in-situ ionic liquid based dispersive liquid?liquid microextraction method for enrichment of tetracyclines before liquid chromatographic analysis has been improved. A 1-benzyl-3- methylimidazolium chloride was used as an ionic liquid. To increase extraction efficiency, some optimization parameters (amount of ammonium hexafluorophoshate, extraction time, centrifugation time, ratio of ionic liquid/salt) were investigated. At optimized conditions, enrichment factors of four tetracycline antibiotics (tetracycline, chlortetracycline, methacycline, doxycycline) were between 25 and 98. The residues of tetracyclines were not found in the studied real samples. For the accuracy of the method, the concentration of 50 and 250 μg/L of standard tetracycline mixture solutions were spiked to the blank real milk, honey and egg samples and the percentage recoveries were obtained in the range of 75.8–109.7%.     

Determination of BTEX Compounds by Dispersive Liquid–Liquid Microextraction with GC–FID

Rapid, inexpensive, and efficient sample-preparation by dispersive liquid–liquid microextraction (DLLME) then gas chromatography with flame ionization detection (GC–FID) have been used for extraction and analysis of BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) in water samples. In this extraction method, a mixture of 25.0 μL carbon disulfide (extraction solvent) and 1.00 mL acetonitrile (disperser solvent) is rapidly injected, by means of a syringe, into a 5.00-mL water sample in a conical test tube. A cloudy solution is formed by dispersion of fine droplets of carbon disulfide in the sample solution. During subsequent centrifugation (5,000 rpm for 2.0 min) the fine droplets of carbon disulfide settle at the bottom of the tube. The effect of several conditions (type and volume of disperser solvent, type of extraction solvent, extraction time, etc.) on the performance of the sample-preparation step was carefully evaluated. Under the optimum conditions the enrichment factors and extraction recoveries were high, and ranged from 122–311 to 24.5–66.7%, respectively. A good linear range (0.2–100 μg L⁻¹, i.e., three orders of magnitude; r ² = 0.9991–0.9999) and good limits of detection (0.1–0.2 μg L⁻¹) were obtained for most of the analytes. Relative standard deviations (RSD, %) for analysis of 5.0 μg L⁻¹ BTEX compounds in water were in the range 0.9–6.4% (n = 5). Relative recovery from well and wastewater at spiked levels of 5.0 μg L⁻¹ was 89–101% and 76–98%, respectively. Finally, the method was successfully used for preconcentration and analysis of BTEX compounds in different real water samples.

     

Determination of Phthalate Esters in Wine Using Dispersive Liquid–Liquid Microextraction and Gas Chromatography

A simple and rapid efficient method was developed for the determination of phthalate esters using dispersive liquid–liquid microextraction followed by gas chromatography with flame ionization detection. A mixture of isopropanol (0.75 mL, dispersant) and carbon tetrachloride (30 µL, extractant) with sodium chloride (1%, w/v) was used for extraction. Under optimum conditions, the method provided linear calibration curves between 0.5 and 200 µg L^?1 for dibutyl phthalate, and 1.0 and 200 µg L^?1 for butyl benzyl phthalate, diethyl phthalate, and diisooctyl phthalate. The relative standard deviations for intra-day and inter-day analyses were less than 5.8% and 6.9%, respectively, with enrichment factors between 229 and 424. Two wine samples were analyzed with recoveries between 70.1% and 119.3%.     

Determination of Herbicides in Soil by Dispersive Solid-Phase Extraction,Dispersive Liquid–Liquid Microextraction,and High-Performance Liquid Chromatography

A method for determination of five herbicides (i.e., quinclorac, metsulfuron-methyl, bensulfuron-methyl, atrazine, prometryn) in soil was developed by dispersive solid-phase extraction combined with dispersive liquid–liquid microextraction and high-performance liquid chromatography. The analytes were removed from the soil by liquid partitioning with acetonitrile/5% acetic acid, purified using a octadecylsilane sorbent, and subsequently extracted before chromatographic analysis. Under the optimized conditions, the linear dynamic range was from 10.0 to 300 ng g^?1 with correlation coefficients (r) between 0.9971 and 0.9985. The limits of detection were between 1.5 and 3.1 ng g^?1, with relative standard deviations from 3.8% to 6.7% (n = 5). The recovery of the herbicides from soil at fortification levels of 20.0 and 100.0 ng g^?1 were between 71.5% and 94.3%. The method was successfully applied to the determination of the analytes in soil.     

LC Determination of Trace Amounts of Phenoxyacetic Acid Herbicides in Water after Dispersive Liquid–Liquid Microextraction

Dispersive liquid–liquid microextraction (DLLME) for extraction and preconcentration of phenoxyacetic acid herbicides in water samples is described. After adjusting the pH to 1.5, the sample was extracted in the presence of 10% w/v sodium chloride by injecting 1 mL acetone as disperser solvent containing 25 μL of chlorobenzene as extraction solvent. The effect of parameters, such as the nature and amount of extraction and disperser solvents, ionic strength of the sample, pH, temperature and extraction time were optimized. DLLME was followed by LC for the determination of 2,4-dichlorophenoxyacetic acid and 4-chloro-2-methyl phenoxyacetic acid. The method had good linearity and a wide linear dynamic range (0.5–750 μg L^?1) with a detection limit of 0.16 μg L^?1 for both the PAAs, making it suitable for their determination in water samples.     

Determination of Aristocularine Enantiomers by Dispersive Liquid–Liquid Microextraction and Chiral High-performance Liquid Chromatography

Here is reported a novel analytical approach for the extractive separation and determination of enantiomeric ratios of aristocularine in bovine serum albumin. The results demonstrate suitable analytical performances. The separation was performed by chiral high-performance liquid chromatography with a 5-µm column using a mobile phase of 1:1 n-hexane:ethanol at a flow rate of 0.7?mL?min^?1 with ultraviolet–visible absorption, circular dichroism, and polarimetric detection. The enantiomers were eluted at 13.2 and 15.6?min for (+) and (?)-aristocularine, with a resolution of 1.58 and a separation factor of 1.27. The analytical parameters for the dispersive liquid–liquid microextraction were optimized; under these conditions, the extraction recoveries were from 88.6% to 93.9% for a two-step extraction. The precision, reported as the percent relative standard deviation, had values from 2.9% to 3.2% for 0.5?µg?mL^?1 of analyte for five replicate measurements using ultraviolet–visible absorption and circular dichroism detection. The limits of detection were between 0.05 and 0.08?µg?mL^?1 with enrichment ratios up to a value of 12.     

Determination of Two Pesticides in Soils by Dispersive Liquid–Liquid Microextraction Combined with LC-Fluorescence Detection

In the present work, a simple, rapid and sensitive sample pre-treatment technique, dispersive liquid–liquid microextraction (DLLME) coupled with liquid chromatography-fluorescence detection (LC-FLD), has been developed to determine carbamate (carbaryl) and organophosphorus (triazophos) pesticide residues in soil samples. Methanol was first used as extraction solvent for the extraction of pesticides from the soil samples and then as dispersive solvent in the DLLME procedure. Under the optimum extraction conditions, the linearity was obtained in the concentration range of 0.1–1,000 ng g^?1 for carbaryl and 1–5,000 ng g^?1 for triazophos, respectively. Correlation coefficients varied from 0.9997 to 0.9999. The limits of detection (LODs), based on signal-to-noise ratio (S/N) of 3, ranged from 14 to 110 pg g^?1. The relative standard deviation (RSDs, for 20.0 ng g^?1 of each pesticide) varied from 1.96 to 4.24% (n = 6). The relative recoveries of two pesticides from soil A1, A2 and A3 at spiking levels of 10.0, 20.0 and 50.0 ng g^?1 were in the range of 88.2–108.8%, 80.8–110.7% and 81.0–111.1%, respectively. The results demonstrated that DLLME was a sensitive and accurate method to determine the target pesticides, at trace levels, in soils.     

Comparison of Headspace-Single Drop Microextraction and Dispersive Liquid–Liquid Microextraction for Determination of Benzene in Juice Drinks Containing Vitamin C

In this paper, a fast and effective headspace-single drop microextraction (HS-SDME) method was applied for the determination of traces of benzene in juice drinks containing vitamin C. Benzene is produced in drinks as a result of interaction of sodium benzoate (as food preservative) and ascorbic acid (vitamin C). A mixture of n-hexadecane and n-dodecane was used as extractant in the form of organic drop. Other parameters affecting the extraction of benzene, including volume of organic drop, time of extraction, volume, pH and ionic strength of sample solution, were studied and optimized. The obtained dynamic range under optimised conditions was from 2 to 350 μg L⁻¹ with the limit of detection of 1.49 μg L⁻¹. The obtained data for HS-SDME of benzene were compared with the data obtained for the determination of benzene with dispersive liquid–liquid microextraction (DLLME). It was observed that though DLLME is simpler and faster, the limit of detection and the repeatability of HS-SDME were better.

     

Determination of Phthalates in Milk by Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction and Gas Chromatography–Mass Spectrometry

Ultrasound-assisted dispersive liquid–liquid microextraction was coupled with gas chromatography—mass spectrometry for the determination of phthalate esters in milk. Dimethyl phthalate, diethyl phthalate, dibutyl phthalate, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, and dioctyl phthalate were analyzed in five brands of pasteurized Turkish milk. The efficiencies of the extraction procedure for the analytes were between 66 and 100%. The linear dynamic ranges of the calibration curves were from 0.025 to 1.000 µg/mL with correlation coefficients exceeding 0.99. The precision of the method is acceptable with relative standard deviation values below 5%. Dibutyl phthalate and bis(2-ethylhexyl) phthalate were commonly observed in milk.     

Dispersive Liquid–Liquid Extraction Based on Freezing of the Organic Drop, Followed by GC for the Determination of Methyl Methacrylate in Wastewater

Crude oil reservoirs typically contain more water than oil, which is emulsified with the oil. During oil production, the emulsion is broken with demulsifiers. Most recently, based on methyl methacrylate, after which, the water, containing the methyl methacrylate, is discharged into surface waters. Significant health hazards have been associated with methyl methacrylate, and a limit of 30 ppm in ground waters has been established. This paper describes the preconcentration of methyl methacrylate from the separated water, using dispersive liquid–liquid microextraction, followed by freezing of the organic drop in an ice bath which facilitated separation of the phases (by centrifugation). In the optimized method, 15.0 μL of 2-dodecanol was rapidly injected into 5 mL water samples, followed by stirring, freezing, and decantation, then direct injection into the gas chromatograph equipped with a flame ionization detector. The method was optimized for: choice of extraction solvent, volume of extraction solvent, pH, ionic strength, temperature and extraction time.     

Determination of Anilines and Toluidines in Water by Salt-Assisted Dispersive Liquid–Liquid Microextraction Combined with GC-FID

Dispersive liquid–liquid microextraction (DLLME) assisted with salting-out was applied for the determination of five aromatic amines in water samples by using gas chromatography with flame ionization detection. In this extraction method, several factors influencing the extraction efficiency of the target analytes, such as extraction and disperser solvent type and their volume, salt addition and amount, and pH, were studied and optimized. Under the optimal DLLME conditions, good linearity was observed in the range of 4–1,000 ng mL^?1 with the RSDs from 1.2 to 7.9 %. The LODs based on S/N of 3 ranged from 0.2 to 3.4 ng mL^?1 and the enrichment factors ranged from 207 to 4,315. The proposed method was successfully applied to the water samples collected from the tap and the lake, and the relative recoveries were in the range of 87.7–108.4 %.     

Determination of Anilines and Toluidines in Water by Salt-Assisted Dispersive Liquid–Liquid Microextraction Combined with GC-FID

Dispersive liquid–liquid microextraction (DLLME) assisted with salting-out was applied for the determination of five aromatic amines in water samples by using gas chromatography with flame ionization detection. In this extraction method, several factors influencing the extraction efficiency of the target analytes, such as extraction and disperser solvent type and their volume, salt addition and amount, and pH, were studied and optimized. Under the optimal DLLME conditions, good linearity was observed in the range of 4–1,000 ng mL⁻¹ with the RSDs from 1.2 to 7.9 %. The LODs based on S/N of 3 ranged from 0.2 to 3.4 ng mL⁻¹ and the enrichment factors ranged from 207 to 4,315. The proposed method was successfully applied to the water samples collected from the tap and the lake, and the relative recoveries were in the range of 87.7–108.4 %.

     

Simultaneous Derivatization and Dispersive Liquid–Liquid Microextraction for Fatty Acid GC Determination in Water

Simultaneous derivatization and dispersive liquid–liquid microextraction technique for gas chromatographic determination of fatty acids in water samples is presented. One hundred microlitre of ethanol:pyridine (4:1) were added to 4 mL aqueous sample. Then a solution containing 0.960 mL of acetone (disperser solvent), 10 μL of carbon tetrachloride (extraction solvent) and 30 μL of ethyl chloroformate (derivatization reagent) were rapidly injected into the aqueous sample. After centrifugation, 1 μL sedimented phase with the analytes was analyzed by gas chromatography. The effects of extraction solvent type, derivatization, extraction, and disperser solvents volume, extraction time were investigated. The calibration graphs were linear up to 10 mg L^?1 for azelaic acid (R ² = 0.998) and up to 1 mg L^?1 for palmitic and stearic acids (R ² = 0.997). The detection limits were 14.5, 0.67 and 1.06 μg L^?1 for azelaic, palmitic, and stearic acids, respectively. Repeatabilities of the results were acceptable with relative standard deviations (RSD) up to 13%. A possibility to apply the proposed method for fatty acids determination in tap, lake, sea, and river water was demonstrated.     

Dispersive Liquid–Liquid Microextraction Coupled with High-Performance Liquid Chromatography for Determination of Coumarin Compounds in Radix Angelicae Dahuricae

In this paper, two methods, organic solvent dispersive liquid–liquid microextraction (OS-DLLME) and ionic liquid dispersive liquid–liquid microextraction (IL-DLLME), coupled with high-performance liquid chromatography have been critically compared and introduced for the analysis of the eight coumarin compounds (psoralen, isopsoralen, bergapten, isobergapten, oxypeucedanin, imperatorin, osthole, and isoimperatorin) in Radix Angelicae Dahuricae samples. Experimental conditions have been investigated for both OS-DLLME and IL-DLLME. Under optimal conditions, the detection limits of the eight coumarin compounds obtained by OS-DLLME and IL-DLLME ranged between 0.002–0.026 ng mL⁻¹ and 0.013–0.66 ng mL⁻¹, respectively. The relative standard deviations (RSDs, n = 9) were lower than 8.7 and 8.4% with enrichment factors in the range of 145–380 and 130–230 folds for OS-DLLME and IL-DLLME, respectively. The results showed that there were no significant deviations between the two DLLME methods for the determination of the eight coumarin compounds. Both methods were simple, fast, efficient, and inexpensive. However, compared with IL-DLLME, the OS-DLLME technique exhibited a higher extraction capacity for the eight target analytes.