Dispersive Liquid–Liquid Microextraction of Silver Prior to Determination by Microsample Introduction-Flame Atomic Absorption Spectrometry

Abstract

A new simple and sensitive method has been proposed for rapid determination of trace levels of silver in environmental water samples, using dispersive liquid–liquid microextraction (DLLME) prior to its microsample introduction-flame atomic absorption spectrometry. Under the optimum conditions, the linear range was 0.1–7 µg L^?1 and limit of detection was 0.018 µg L^?1. The relative standard deviation for 0.50 and 5.00 µg L^?1 of silver in water sample was 4.0 and 1.7%, respectively. The relative recoveries of silver from tap, well, river, and seawater samples at spiking levels of 1.00 and 5.00 µg L^?1 were in the range of 86.4–98.6%.     

Ligandless,Task-Specific Ionic Liquid-Based Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for the Determination of Cobalt Ions by Electrothermal Atomic Absorption Spectrometry

Ligandless, task-specific ionic liquid based ultrasound-assisted dispersive liquid–liquid microextraction (TSIL-USA-DLLME) was used for preconcentration of cobalt ions in food and water samples and in vitamin supplements before analysis by electrothermal atomic absorption spectrometry. The reported method is free of toxic volatile organic solvents and does not require the use of a back-extraction step. The dispersion of extractant was achieved with the use of ultrasound. A TSIL, trioctylmethylammonium thiosalicylate (TOMATS), was served as both the extraction and complexing agent. After microextraction, the TOMATS phase was separated by centrifugation and dissolved in ethanol before analysis. Selected parameters affecting the microextraction including the pH of the sample, the volume of the ionic liquid, the ultrasonication time, centrifugation parameters, and the influence of ionic strength were optimized. The limit of detection was 0.011?ng?mL^?1 for cobalt ions. The achieved preconcentration factor was 24. The relative standard deviations for the determination of analyte in the real samples were 3–24%. The accuracy of this method was evaluated by the extraction and determination of the analyte in several certified reference materials including INCT-SBF-4 (soya bean flour), INCT-TL-1 (tea leaves), ERM-CAO11b (hard drinking water), INCT-MPH-2 (mixed Polish herbs), TMDA-54.5 (Lake Ontario Water), and NIST 1643e. The measured cobalt contents were in satisfactory agreement with the certified concentrations based on Student’s t-test at the 95% confidence level. The presented method has been successfully applied for the determination of analyte in real samples that include tea, lake water, and vitamin supplements.     

Dispersive Liquid–Liquid Microextraction of Nickel Prior to Its Determination by Microsample Injection System-Flame Atomic Absorption Spectrometry

A sensitive and simple method for the determination of trace nickel was developed by the combination of dispersive liquid–liquid microextraction (DLLME) and microsample injection system–flame atomic absorption spectrometry (MIS–FAAS). Trace nickel was preconcentrated as the 8-hydroxyquinoline chelate by DLLME, and the conditions were optimized by a Plackett-Burman design. Quantitative recovery of nickel (98 ± 1%) was obtained by a sample volume of 7.5 mL at a pH of 6.0. The enrichment factor was 52.5, and the limits of detection and quantitation were 0.1 µ g L^?1 and 3.0 µ g L^?1, respectively. The method was validated by the analysis of a wastewater standard reference material, water samples, and a wire sample. The reported method has superior analytical figures of merit compared with similar methods reported in the literature.     

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.     

Determination of Ultratrace Amounts of Copper（ Ⅱ ） in Water Samples by Electrothermal Atomic Absorption Spectrometry After Cloud Point Extraction

IntroductionIn environment, copper is usually found in traceor ultratrace levels, and its detection requires sensitiveinstrumental measuring techniques such as electrother-mal atomic absorption spectrometry(ETAAS) and ICP-AES or ICP-MS. Frequently, a prec…     

Sensitive and Accurate Determination of Cobalt at Trace Levels by Slotted Quartz Tube-Flame Atomic Absorption Spectrometry Following Preconcentration with Dispersive Liquid–Liquid Microextraction

Slotted quartz tube-flame atomic absorption spectrometry (SQT-FAAS) was used as a sensitive technique for the determination of cobalt, an element has toxic effects on living organisms at high doses. For the preliminary preconcentration of cobalt prior to the analysis, dispersive liquid–liquid microextraction (DLLME) was used. The instrument is equipped with a SQT to further increase the sensitivity by increasing the residence time of cobalt atoms in the light path emitted by a hollow cathode lamp. In the complex formation step, pH, the volume of buffer solution, the concentration of 1,5-diphenylcarbazone, and the volume of ligand were optimized. In addition, all of the system parameters, including the type and volume of the extraction solvent, dispersant type and volume of solvent, type of salt and the volume for the dispersion liquid–liquid microextraction, were optimized to obtain the lowest detection limit. Under the optimum conditions, the detection power of FAAS was improved by a factor of 86.56 fold using DLLME-SQT-FAAS. The limit of detection for the DLLME-SQT-FAAS system was 0.97?µg L^?1. The applicability of the developed method was verified in tap and waste water samples by spiking measurements. The percentage recovery values for these were determined to be 91.7% and 111.0%, respectively.     

Determination of Mercury(II) in Drinking Water by Total Reflection X-ray Fluorescence Spectrometry and Liquid–Liquid Microextraction

The total reflection X-ray fluorescence determination of mercury(II) in drinking water at concentrations of 7?×?10^?2 to 3.0?µg/L is reported. The mercury(II) preconcentration protocol includes directly suspended droplet microextraction with benzene as a molecular iodine complex. The proposed approach is highly selective. The elements Cr, Mn, Fe, Co, Ni, Zn, and Pb at concentrations up to 0.1?g/L did not interfere with the extraction of trace mercury(II). The method is characterized by high sensitivity (limit of detection of 21?ng/L) and suitable reproducibility (relative standard deviation of 0.12 for 100?ng/L). The accuracy of the results was confirmed by recovery and the method of standard addition.     

Speciation of Arsenic in Drinking Water by Dispersive Liquid–Liquid Microextraction,Graphite Furnace Atomic Absorption Spectrometry,and Orthogonal Array Design

Orthogonal array design was used to optimize arsenic speciation in drinking water in contact with materials by dispersive liquid–liquid microextraction followed by graphite furnace atomic absorption spectrometry. Arsenic speciation was achieved by the formation of an arsenic(III) hydrophobic complex with a new chelating agent, 1,2,6-hexanetriol trithioglycolate, at neutral pH. The complex was extracted into the organic phase, while arsenic(V) remained in aqueous solution. The concentration of As(V) was determined by subtracting As(III) from the total arsenic following the reduction of As(V) to As(III) by L-cysteine. Orthogonal array design with OA₁₆ (44) and OA₉ (33) matrices was used to optimize the efficiency of dispersive liquid–liquid microextraction and the reduction of As(V) to As(III), respectively. Under the optimal conditions, the detection limit was 0.03?µg?L^?1 for As(III) and the relative standard deviation was 5.9% with an enhancement factor of 87. The calibration curve was linear from 0.19 to 3.0?µg?L^?1 with a correlation coefficient of 0.9996. The developed method was used for arsenic speciation in solutions of drinking water that contacted materials. The recoveries of fortified samples were in an acceptable range from 92.0 to 113.3%.     

Determination of Estrone and 17β-Estradiol in Water Samples Using Dispersive Liquid–Liquid Microextraction Followed by LC

A new method, termed dispersive liquid–liquid microextraction (DLLME), was developed for the extraction and pre-concentration of estrone (E1) and 17β-estradiol (E2) in water samples. The samples were extracted by 0.50 mL methanol (disperser solvent) containing 25.0 μL tetrachloroethane (extraction solvent). Important factors such as the volume and type of extraction and disperser solvent, extraction time and salt effect were studied. Under optimum conditions, the enrichment factors and the limits of detection were 347 and 0.2 ng mL^?1 for E1, and 203 and 0.1 ng mL^?1 for E2, respectively. The linear range was 0.5–5,000 ng mL^?1. Compared to other methods, DLLME–LC–VWD has advantages for E1 and E2 analysis in water: high enrichment factor, low cost, simplicity, quick and easy operation.     

Determination of Arsenic in Food Samples by Hydride Generation – Atomic Absorption Spectrometry

A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34µgL^–1 and 1.2µgL^–:1, respectively, and the analytical curve is linear up to 30.0µgL^–1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0µgL^–1 As and 1.8% for 30.0µgL^–1 As, with an injection frequency of up to 135h^–1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0molL^–1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans.     

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.     

Ultra-Preconcentration and Determination of Multiple Pesticide Residues in Water Samples Using Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction and GC-FID

In this study, a simple and efficient method has been developed to analyze pesticides in water samples using ultrasonic-assisted dispersive liquid–liquid microextraction (UA-DLLME) combined with gas chromatography-flame ionization detection (GC-FID). Several parameters, including type and volume of extractant and dispersant, extraction time, and amount of salt on extraction performance, were optimized in detail. A mixture of acetonitrile (1.0 mL, dispersant) and carbon tetrachloride (15 μL, extractant) was used for extraction. Under optimal conditions, enrichment factors were obtained between 315 and 1153. The linearity of the method ranged from 1 to 100 μg L⁻¹ with correlation coefficients ≥0.9990. Limits of detection (S/N = 3) ranged between 0.09 and 0.57 μg L⁻¹, depending on the compounds. Relative standard deviations were <8.0 % (n = 5) for both intra- and inter-day analyses. The proposed method was successfully applied for the preconcentration and determination of pesticides in water samples (river water, tap water, and lake water) with recoveries that varied from 90.5 to 107.7 %.

     

Ultra-Preconcentration and Determination of Multiple Pesticide Residues in Water Samples Using Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction and GC-FID

In this study, a simple and efficient method has been developed to analyze pesticides in water samples using ultrasonic-assisted dispersive liquid–liquid microextraction (UA-DLLME) combined with gas chromatography-flame ionization detection (GC-FID). Several parameters, including type and volume of extractant and dispersant, extraction time, and amount of salt on extraction performance, were optimized in detail. A mixture of acetonitrile (1.0 mL, dispersant) and carbon tetrachloride (15 μL, extractant) was used for extraction. Under optimal conditions, enrichment factors were obtained between 315 and 1153. The linearity of the method ranged from 1 to 100 μg L^?1 with correlation coefficients ≥0.9990. Limits of detection (S/N = 3) ranged between 0.09 and 0.57 μg L^?1, depending on the compounds. Relative standard deviations were <8.0 % (n = 5) for both intra- and inter-day analyses. The proposed method was successfully applied for the preconcentration and determination of pesticides in water samples (river water, tap water, and lake water) with recoveries that varied from 90.5 to 107.7 %.     

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.     

Determination of Cadmium in Human Serum and Blood Samples after Dispersive Liquid–Liquid Microextraction Using a Task-Specific Ionic Liquid

Task-specific ionic liquid dispersive liquid–liquid microextraction (TSIL-DLLME) is a simple and rapid preconcentration approach for the measurement of cadmium in serum and blood samples of human subjects. In this method a novel task-specific ionic liquid, trioctylmethyl ammonium thiosalicylate (TOMATS), which has dual characteristics as a chelating agent and extractive solvent, was investigated. TOMATS complexes with Cd due to the chelating effect of the ortho-positioned carboxylate relative to the thiol functionality. The assessment of the optimum values of variables including the pH, amount of reagents (TOMATS, diluents, Triton X114, and back extracting acid solution), temperature, and incubation time, which affect the recoveries of analyte by TSIL-DLLME method were studied. After enrichment experiments, acidic solution was used to back extract the metal ions from the ionic liquid rich phase and with determination by electrothermal atomic absorption spectrometry. Using the optimal experimental conditions, the limit of detection (3?s), precision (relative standard deviation), preconcentration, and enhancement factors of developed method for Cd were found to be 0.05?µg/L, greater than 5%, 62.5, and 52.8, respectively. To check the accuracy of the developed method, certified reference material of serum and blood were analyzed by the developed method, and the measured values of Cd were in good agreement with the certified values. The developed method was applied successfully to determine Cd in blood and serum samples of lymphatic cancer patients relative to healthy controls.     

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 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 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 %.     

Speciation of Antimony in Soils and Sediments by Liquid Chromatography–Hydride Generation–Atomic Fluorescence Spectrometry

The methodology for antimony speciation was optimized for liquid chromatography coupled to hydride generation – atomic fluorescence spectrometry. An anion exchange column was employed with isocratic elution. Ammonium tartrate was shown to be the optimum mobile phase and extracting solution for this analysis. The highest efficiency and resolution for the antimony species was achieved using 5 percent methanol in 300 millimoles per liter ammonium tartrate acidified with hydrochloric acid to pH 4.5. The retention times of antimony(V), trimethylantimony, and antimony(III) were 2.6, 3.9, and 5.2 minutes, respectively. The calibration curves were linear with limits of detection of 0.1, 0.2, and 0.43 microgram per liter for antimony(III), antimony(V), and trimethylantimony, respectively. The precision, evaluated by the relative standard deviation, ranged from 1.2 to 5.3 percent. The average recovery from these environmental samples by a single-step procedure was approximately 26 percent. The results also revealed that the correlation between the sum of each species by the single-step procedure and total digestion was significant for the investigated soils and sediments.     

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 %.