Determination of Six Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC-NPD

A single-drop microextraction (SDME) procedure with a modified microsyringe was developed for the analysis of six organophosphorus pesticides (OPPs) in water. Microsyringe was modified by attaching a 2-mm cone onto the needle tip end. The conditions affecting SDME performance including microextraction solvent, stirring speed, extraction time, ionic strength and sample pH were optimized. Under the optimized conditions, the linear ranges of the SDME with ethion as internal standard were 0.05–50 μg L^?1 (except for dimethoate 5–5,000 μg L^?1) and limits of detection (LOD) were 0.012–0.020 μg L^?1 (except for dimethoate 0.45 μg L^?1). Recoveries of six pesticides were in the range of 70.6–107.5 % with relative standard deviation lower than 6.0 %. The modified method is simple, rapid and sensitive, and acceptable in the analysis of OPPs pesticides in water samples.     

Determination of Mycotoxins Using Hollow Fiber Dispersive Liquid–Liquid–Microextraction (HF-DLLME) Prior to High-Performance Liquid Chromatography – Tandem Mass Spectrometry (HPLC - MS/MS)

A modified hollow-fiber-supported dispersive liquid-liquid microextraction (HF-DLLME) method was developed for the determination of aflatoxins and ochratoxin A in food samples. The various parameters affecting the efficiency of extraction, such as pH, salt addition, extraction time, stirring rate, desorption time, type and volume of extractant and disperser solvents were carefully studied and optimized using two step strategies. The linearity of the evaluated results was 0.1 to 30?μg L^?1 for aflatoxins and 0.1 to 20?μg L^?1 for ochratoxin A, with regression coefficients (R²) exceeding 0.9990. The precision was satisfactory with relative standard deviation values less than 11%. The method accuracy was within the recommended range from 70% to 120% and analyte accuracy between 83% and 101%. The limits of detection and quantification were in the range from 0.04 to 0.06?μg L^?1 and 0.08 to 0.13?μg L^?1, respectively, for multi-aflatoxins, and 0.02 to 0.04?µg L^?1 and 0.08 to 0.10?µg L^?1, respectively, for ochratoxin A. The developed method was successfully applied for the determination of mycotoxins in food samples.     

Analysis of PAHs in Water and Fruit Juice Samples by DLLME Combined with LC-Fluorescence Detection

A simple, rapid and efficient method termed dispersive liquid–liquid microextraction combined with liquid chromatography-fluorescence detection, has been developed for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in water and fruit juice samples. Parameters such as the kind and volume of extraction solvent and dispersive solvent, extraction time and salt effect were optimized. Under optimum conditions, the enrichment factors ranged from 296 to 462. The linear range was 0.01–100 μg L^?1 and limits of detection were 0.001–0.01 μg L^?1. The relative standard deviations (RSDs, for 5 μg L^?1 of PAHs) varied from 1.0 to 11.5% (n = 3). The relative recoveries of PAHs from tap, river, well and sea water samples at spiking level of 5 μg L^?1 were 82.6–117.1, 74.9–113.9, 77.0–122.4 and 86.1–119.3%, respectively. The relative recoveries of PAHs from grape and apple juice samples at spiking levels of 2.5 and 5 μg L^?1 were 80.8–114.7 and 88.9–123.0%, respectively. It is concluded that the proposed method can be successfully applied for determination of PAHs in water and fruit juice samples.     

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.

     

Application of DLLME Based on the Solidification of Floating Organic Droplets for the Determination of Dinitrobenzenes in Aqueous Samples

Dispersive liquid–liquid microextraction (DLLME) based on the solidification of floating organic droplets (DLLME-SFO) combined with gas chromatography-electron-capture detection (GC–ECD) has been developed for extraction and analysis of three dinitrobenzenes. The extraction conditions including extraction solvent, disperser solvent, extraction time, salt effect and temperature were investigated and optimized systematically. The limits of detection were 0.019 μg L^?1 for 1,4-dinitrobenzene, 0.079 μg L^?1 for 1,3-dinitrobenzene and 0.034 μg L^?1 for 1,2-dinitrobenzene. Moreover, it offered good repeatability and high recovery. This method was successfully applied to monitor DNBs in different water samples.     

Determination of Trace Chloroanilines in Environmental Water Samples Using Hollow Fiber-Based Liquid Phase Microextraction

A liquid phase microextraction method using hollow fiber to support extraction solvent was developed for enrichment of trace level chloroanilines in environmental water samples. Target analytes, 2-chloroaniline, 3-chloroaniline, 2,3-dichloroaniline, 2,4-dichloroaniline, 3,4-dichloroaniline, and 3,5-dichloroaniline were determined using gas chromatography-flame ionization detector after extraction. Experimental conditions that affect extraction efficiency were investigated and optimized. The proposed method showed a wide linear range from lower ??g L^?1 to 1,000 ??g L^?1, low detection limits (??5.1 ??g L^?1), and reasonable relative standard deviations (RSDs < 13%). Feasibility of the method was evaluated by analyzing river water samples collected from the Hudson River and the East River in New York City.     

Large Volume Headspace Analysis Using Solid-Phase Microcolumn Extraction

A rapid and simple large volume headspace (HS) sampling technique termed headspace solid-phase microcolumn extraction (HS-SPMCE) is described. HS gas above a liquid or solid sample is aspirated by attaching a gas-tight syringe onto a glass thermal desorption tube filled with Tenax sorbent. The trapped analytes are recovered by thermal desorption for gas chromatography–mass spectrometry (GC–MS) analysis. Benzene, toluene, ethylbenzene and the xylene isomers (BTEX) are used as model compounds to demonstrate the application of the extraction procedure for water samples. The results of the tests of the effect of agitation time and aspiration rate on recovery of the analytes show a good robustness of the method. BTEX are determined in the linear range from 0.5 to 50.0 μg L^?1 with limits of detection (3 σ) ranging within 0.09–0.14 μg L^?1 (MS was in scan mode). The method provides a good repeatability (RSD < 9%) and only a negligible carryover effect was observed ( ≤0.05%) when analysing BTEX at concentration 50.0 μg L^?1.     

Preparation of a Robust and Sensitive Gold-Coated Fiber for Solid-Phase Microextraction of Polycyclic Aromatic Hydrocarbons in Environmental Waters

A robust gold-coated solid-phase microextraction fiber was rapidly prepared on an etched stainless-steel wire based on chemical deposition. Gold(III) was reduced to produce a mechanically robust fiber with a stable coating. Subsequently, it was applied for solid-phase microextraction of five polycyclic aromatic hydrocarbons in water samples coupled to high performance liquid chromatography with an ultraviolet-visible detector. The preconcentration conditions were optimized, including extraction and desorption time, temperature, stirring rate, and ionic strength. Under the optimized conditions, the calibration graphs were linear in the range from 1 to 500 µg · L^?1 for naphthalene and 0.20–500 µg · L^?1 for phenanthrene, anthracene, fluoranthene, and pyrene. Limits of detection were between 0.016 and 0.22 µg · L^?1 (signal-to-noise ratio = 3). The analysis of water samples showed that the recoveries ranged from 86.0% to 112.9% with relative standard deviations between 2.03% and 11.7%. The fiber coating was sensitive and suitable for the preconcentration and determination of polycyclic aromatic hydrocarbons in environmental waters. Compared with previously reported solid-phase microextraction methods, this device offered easy preparation, low cost, resistance to organic solvents, good stability, and high durability.     

Development of ultrasound-assisted emulsification solidified floating organic drop microextraction for determination of trace amounts of iron and copper in water, food and rock samples

A simple and efficient liquid-phase microextraction technique was developed using ultrasound-assisted emulsification solidified floating organic drop microextraction combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of iron and copper in real samples. 2-Mercaptopyridine n-oxide was used as chelating agent and 1-dodecanol was selected as extraction solvent. The factors influencing the complex formation and extraction were optimized. Under optimum conditions, an enrichment factor of ~13 was obtained for both iron and copper from only 6.7 mL of aqueous phase. The analytical curves were linear between 40–800 and 20–1,200 μg L^?1 for iron and copper respectively. Based on three SD of the blank, the detection limits were 8.6 and 4.1 μg L^?1 for iron and copper respectively. The relative SDs for ten replicate measurements of 500 μg L^?1 of metal ions were 2.9 and 1.2 for iron and copper respectively. The proposed method was successfully applied for determination of iron and copper in environmental waters and some food samples including chess, rice, honey and powdered milk. Finally, method validation was made using rock certified reference material. A student’s t test indicated that there was no significant difference between experimental results and certified values.     

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 %.     

Electrochemically controlled solid-phase micro-extraction of proline using a nanostructured film of polypyrrole, and its determination by ion mobility spectrometry

We report on a fast, simple and accurate method for the determination of proline in urine samples by employing a nanostructured film of conducting polypyrrole for electrochemically controlled solid-phase microextraction, and ion mobility spectrometry (IMS) for detection. This method has the advantages of simple sample preparation and a sensitivity of IMS to proline that is higher than that for other amino acids. The calibration curve is linear in the range of 0.5–60 μg L^?1 (4–521 nmol L^?1), and the detection limit is 0.2 μg L^?1. The electrochemical potentials for uptake and release were optimized. The method was successfully applied to the clean-up and quantitation of trace amounts of proline in urine samples.

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58 μg L^?1, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000 μg L^?1. The ranges of intra- and interday precision (n = 5) at 100 μg L^?1 of nitrophenols were 5.85–7.76 and 10.2–11.9 %, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.     

Determination of Methadone in Biological Samples Using Liquid Phase Microextraction with Back Extraction Combined with LC

Liquid phase microextraction with back extraction (LPME-BE) combined with liquid chromatography-ultra violet (LC-UV) was applied for the extraction and determination of methadone in biological fluids. At the optimized conditions, an enrichment factor of 386 and detection limit (LOD) of 0.2 μg L^?1 were obtained. The calibration curve was linear (r ² = 0.989) in the concentration range of 0.6–1,000 μg L^?1. Within-day relative standard deviation RSD (S/N = 3) and between-day RSD were 2.7 and 5.9%, respectively. The feasibility of the proposed method was evaluated by extraction and determination of methadone in plasma and urine samples and satisfactory results were obtained.     

Optimization of parameters for the alcoholic-assisted dispersive liquid–liquid microextraction of estrogens in water

Extraction and determination of estrogens in water samples were performed using alcoholic-assisted dispersive liquid–liquid microextraction (AA-DLLME) and high-performance liquid chromatography (UV/Vis detection). A Plackett–Burman design and a central composite design were applied to evaluate the AA-DLLME procedure. The effect of six parameters on extraction efficiency was investigated. The factors studied were volume of extraction and dispersive solvents, extraction time, pH, amount of salt and agitation rate. According to Plackett–Burman design results, the effective parameters were volume of extraction solvent and pH. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 220 μL 1-octanol as extraction solvent, 700 μL ethanol as dispersive solvent, pH 6 and 200 μL sample volume. Linearity was observed in the range of 1–500 μg L^?1 for E2 and 0.1–100 μg L^?1 for E1. Limits of detection were 0.1 μg L^?1 for E2 and 0.01 μg L^?1 for E1. The enrichment factors and extraction recoveries were 42.2, 46.4 and 80.4, 86.7, respectively. The relative standard deviations for determination of estrogens in water were in the range of 3.9–7.2 % (n = 3). The developed method was successfully applied for the determination of estrogens in environmental water samples.     

Use of a Headspace Solid-Phase Microextraction-Based Methodology Followed by Gas Chromatography–Tandem Mass Spectrometry for Pesticide Multiresidue Determination in Teas

This study reports on the development of a fast and efficient method based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–tandem mass spectrometry (GC–MS/MS) for simultaneous analysis of 128 volatile or semi-volatile pesticide residues belonging to nine classes of pesticides. The important factors related to HS-SPME performance were optimized; these factors include fiber types, water volume, ion strength, extraction temperature, and extraction time. The best extraction conditions include a PDMS/DVB fiber, and analytes were extracted at 90 °C for 60 min from 1 g of tea added to 5 mL of 0.2 g mL^?1 NaCl solution. The methodology was validated using tea samples spiked with pesticides at three concentration levels (10, 50, and 100 μg kg^?1). In green tea, oolong tea, black tea, and puer tea, 82.8, 88.3, 79.7, and 84.3% of the targeted pesticides meet recoveries ranging from 70 to 120% with a relative standard deviation of?≤?20%, respectively, when spiked at a level of 10 μg kg^?1. Limits of quantification in this method for most of the pesticides were 1 or 5 μg kg^?1, which are far below their maximum residue limits prescribed by EU. The optimized method was employed to analyze 30 commercial samples obtained from local markets; 17 pesticide residues were detected at concentrations of 2–452 μg kg^?1. Chlorpyrifos was the most detected pesticide in 80% of the samples, and the highest concentration of dicofol (452 μg kg^?1) was found in a puer tea. This is the first time to find that the optimized extraction temperature for pesticide residues is 90 °C, which is much higher than other reported HS-SPME extraction conditions in tea samples. This developed method could be used to screen over one hundred volatile or semi-volatile pesticide residues which belong to multiple classes in tea samples, and it is an accurate and reliable technique.     

Three-dimensional Pd/Pt bimetallic nanodendrites on a highly porous copper foam fiber for headspace solid-phase microextraction of BTEX prior to their quantification by GC-FID

The preparation of bimetallic Pd/Pt nanofoam for use in fiber based solid-phase microextraction (SPME) is described. First, a highly porous copper foam was prepared on the surface of an unbreakable copper wire by an electrochemical method. Then, the substrate was covered with metallic Pd and Pt using galvanic replacement of the Cu nanofoam substrate by applying a mixture of Pd(II) and Pt(IV) ions. The procedure provided an efficient route to modify Pd/Pt nanofoams with large specific surface and low loading with expensive noble metals. The fiber was applied to headspace SPME of benzene, toluene, ethylbenzene and xylene (BTEX) (as the model compounds) in various spiked water and wastewater samples. It was followed by gas chromatography-flame ionization detection (GC-FID). A Plackett-Burman design was performed for screening the experimental factors prior to Box-Behnken design. Compared with the commercial PDMS SPME fiber (100 μm), it had higher extraction efficiency for BTEX. Under the optimum conditions, the method has low limits of detection (0.16–0.35 μg L^?1), a wide linear range (1–200 μg L^?1), relative standard deviations between 5.8 and 10.5%, and good recoveries (>85% from spiked samples).

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Graphical abstract Schematic presentation of a three-dimensional Pd/Pt bimetallic nanodendrites supported on a highly porous copper foam fiber for use in headspace solid phase microextraction of BTEX. They were then quantified by gas chromatography–flame ionization detector.

     

Ionic liquid-based dispersive liquid–liquid microextraction for determination of trace amounts of iron in water, rock and human blood serum samples

A green and sensitive dispersive liquid-phase microextraction procedure based on room-temperature ionic liquid (1-hexyl-3-methylimidazolium hexafluorophosphate) for preconcentration and determination of total iron in real samples prior to flame atomic absorption spectrometry was developed. 2-Mercaptopyridine-N-oxide (pyrithione) and ethanol were used as complexing agent and dispersive solvent in the proposed method, respectively. The factors influencing the extraction were optimized. Under optimum conditions, the enhancement factor of 15 was obtained from only 11.35 mL of aqueous phase. The linear dynamic range and the detection limit were 10.0–700 and 2.4 μg L^?1, respectively. The relative standard deviation (RSD) for ten replicate measurements of 500 μg L^?1 of iron is 3.1 %. The developed method has been successfully applied for the determination of iron in water samples, human blood serum and rock certified reference material with high efficiency.     

Application of vortex-assisted supramolecular solvent liquid–liquid microextraction for trace determination of nitroaniline isomers

A novel, fast and efficient method for the analysis of nitroaniline isomers as model compounds was developed using vortex-assisted supramolecular solvent liquid–liquid microextraction (VA-SMS-LLME). A vortex mixer was used as the mixer in supramolecular solvent liquid–liquid microextraction, and it decreased the extraction time greatly. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, salt effect and extraction time, were optimised in detail. Under the optimal conditions, the enrichment factor was 133 for p-nitroaniline, 98 for m-nitroaniline and 115 for o-nitroaniline, and the limits of detection by HPLC were 0.3, 1.0 and 0.5 μg L^?1, respectively. Linearity with determination coefficient from 0.9981 to 0.9993 was evaluated using water samples spiked with the nitroanilines at fourteen different concentration ranging from 4 to 1000 μg L^?1. The ranges of intra-day and inter-day precision (n = 5) at 10 μg L^?1 of nitroanilines were 1.67–7.05% and 9.4–11.6%, respectively. The VA-SMS-LLME method was successfully applied for preconcentration of nitroanilines in environmental water samples.     

A Sensitive Method for Methyl tert-Butyl Ether Analysis in Water Samples by a New HS-SPME Vial and GC

In this study, a new sample vial has been designed for the extraction and determination of methyl tert-butyl ether (MTBE) in water samples by headspace solid-phase microextraction method. The special feature of this new vial is cooling the HS above the aqueous sample by cold water stream for maximum analyte absorption on SPME fiber coating. The analysis was by a gas chromatograph equipped with flame ionization detector and a capillary column (CP-sil 13 CB). Some significant variables affecting the extraction procedure were optimized. By use of divinylbenzene/carboxen/polydimethylsiloxane fiber, a sample volume of 10 mL, stirring rate of 1,000 rpm, salt concentration of 24%, extraction time of 15 min and extraction temperature of 83 °C, detection limit of 0.022 μg L^?1 and a good linearity (R ² = 0.998) in a calibration range of 0.1–400 μg L^?1 were achieved. The relative standard deviation for triplicate runs ranged between 6 and 8%. The method could be applied to the analysis of trace levels of MTBE in various water samples.     

Rapid Enrichment and Sensitive Determination of Tetrabromobisphenol A in Environmental Water Samples with Ionic Liquid Dispersive Liquid-Phase Microextraction Prior to HPLC–ESI-MS–MS

A new microextraction method termed ionic liquid dispersive liquid-phase microextraction has been developed for the rapid enrichment and sensitive determination of tetrabromobisphenol A in environmental water samples prior to high-performance liquid chromatography–electrospray tandem mass spectrometry. Instead of using toxic organic solvents, green solvent ionic liquid was used as extraction solvent. Factors that may influence the enrichment efficiency, such as type and volume of ionic liquid, type and volume of disperser solvent, sample pH, extraction time and NaCl content were investigated and optimized in detail. Under optimum conditions, linearity of the method was observed over the range 1–100 μg L^?1 with correlation coefficient 0.9986. The proposed method has been found to have excellent sensitivity with limit of detection 0.06 μg L^?1 and precision 6.95% (RSD, n = 5). This method has been successfully applied to analyze real environmental water samples and satisfactory results were achieved. All these results indicated that the present method was an environmentally friendly method for the rapid enrichment and sensitive analysis of tetrabromobisphenol A at trace level in environmental water samples.