Matrix solid-phase dispersion coupled with magnetic ionic liquid dispersive liquid–liquid microextraction for the determination of triazine herbicides in oilseeds

A novel method was developed for the determination of six triazine herbicides from oilseeds by matrix solid-phase dispersion combined with magnetic ionic liquid dispersive liquid–liquid microextraction (MSPD-MIL-DLLME), followed by ultrafast liquid chromatography with ultraviolet detection (UFLC-UV). The MIL, 1-butyl-3-methylimidazolium tetrachloroferrate ([C₄mim][FeCl₄]), was used as the microextraction solvent to simplify the extraction procedure by magnetic separation. The effects of several important experimental parameters, including type of dispersant, ratio of sample to dispersant, type and volume of collected elution solvent, type and volume of MIL, were investigated. Using the present method, UFLC-UV gave the limits of detection (LODs) of 1.20–2.72 ng g⁻¹ and the limits of quantification (LOQs) of 3.99–9.06 ng g⁻¹ for triazine herbicides. The recoveries were ranged from 82.9 to 113.7% and the relative standard deviations (RSDs) were equal or lower than 7.7%. The present method is easy-to-use and effective for extraction of triazine herbicides from oilseeds and shows the potentials of practical applications in the treatment of the fatty solid samples.     

Magnetic field assisted μ-solid phase extraction of anti-inflammatory and loop diuretic drugs by modified polybutylene terephthalate nanofibers

A magnetic nanocomposite consisting of nanoparticles–polybutylene terephthalate (MNPs–PBT) was electrospun and used as an extracting medium for an on-line μ-solid phase extraction (μ–SPE)–high performance liquid chromatography (HPLC) set–up with an ultraviolet (UV) detection system. Due to the magnetic property of the prepared nanofibers, the whole extraction procedure was implemented under an external magnetic field to enhance the extraction efficiencies. The developed method along with the synthesized nanocomposite were found to be appropriate for the determination of trace levels of selected drugs including furosemide, naproxen, diclofenac and clobetasol propionate in the urine sample. The prepared MNPs-PBT electrospun nanocomposite was characterized using the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and Fourier transform infrared (FT–IR) spectroscopy. The prepared magnetic fibers showed high porosity, which was another driving force for the extraction efficiency enhancement. Major parameters affecting the extraction efficiency of the selected drugs were optimized. The limits of detections (LOD) of the studied drugs were in the range of 0.4–1.6 μg L⁻¹ and the limits of quantification (LOQ) were 1–4 μg L⁻¹ under the optimized conditions. Relative standard deviation (RSD%) for three replicates at three concentration levels of 6, 100 and 400 μg L⁻¹ were 5.9–8.0% while acceptable linear range with two orders of magnitude was obtained (R² = 0.99). The method was validated by the determination of the selected drugs in urine samples and the results indicated that this method has sufficient potential for enrichment and determination of the desired drugs in the urine sample. The relative recovery values were found to be in the range of 78–91%. Implementing the developed on–line μ–SPE method under the external magnetic field induction, led to higher extraction efficiencies for the selected drugs with various diamagnetic properties.     

Silica-coated magnetic nanoparticles modified with γ-mercaptopropyltrimethoxysilane for fast and selective solid phase extraction of trace amounts of Cd,Cu, Hg,and Pb in environmental and biological samples prior to their determination by inductively coupled plasma mass spectrometry

We report here the synthesis of a new sorbent comprising silica-coated magnetic nanoparticles (SCMNPs) modified with γ-mercaptopropyltrimethoxysilane (γ-MPTMS) for solid phase extraction of trace amounts of Cd, Cu, Hg, and Pb from biological and environmental samples. The prepared nanoparticles were characterized by infrared spectroscopy, transmission electron microscopy, and static adsorption-desorption experiments. These magnetic nanoparticles carrying the target metals could be easily separated from the aqueous solution simply by applying an external magnetic field; no filtration or centrifugation was necessary. Using this novel magnetic material, we have developed an efficient and cost-effective two-step method for detecting trace amounts of Cd, Cu, Hg, and Pb in environmental and biological samples. The first step of the method is a separation/preconcentration step, in which metals are adsorbed onto γ-MPTMS-SCMNPs. In the second step, inductively coupled plasma mass spectrometry is used to study the adsorbed metals. The effects of pH, sample volume, eluent, and interfering ions have been investigated. Under the optimized conditions, the limits of detection for Cd, Cu, Hg, and Pb were as low as 24, 92, 107, and 56 pg L^− 1, respectively. Relative standard deviations (RSDs, C = 2 ng L^− 1, n = 7) were 6.7%, 9.6%, 8.3%, and 3.7%, respectively.The proposed method has been validated using three certified reference materials, and it has been applied successfully in the determination of trace metals in biological and environmental samples.     

Rapid and effective sample cleanup based on graphene oxide-encapsulated core–shell magnetic microspheres for determination of fifteen trace environmental phenols in seafood by liquid chromatography–tandem mass spectrometry

In this study, graphene oxide-encapsulated core–shell magnetic microspheres (GOE-CS-MM) were fabricated by a self-assemble approach between positive charged poly(diallyldimethylammonium) chloride (PDDA)-modified Fe₃O₄@SiO₂ and negative charged GO sheets via electrostatic interaction. The as-prepared GOE-CS-MM was carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer analysis (VSM), and X-ray photoelectron spectroscopy (XPS), and was used as a cleanup adsorbent in magnetic solid-phase extraction (MSPE) for determination of 15 trace-level environmental phenols in seafood coupled to liquid chromatography–tandem mass spectrometry (LC–MS/MS). The obtained results showed that the GOE-CS-MM exhibited excellent cleanup efficiency and could availably reduce the matrix effect. The cleanup mechanisms were investigated and referred to π–π stacking interaction and hydrogen bond between GOE-CS-MM and impurities in the extracts. Moreover, the extraction and cleanup conditions of GOE-CS-MM toward phenols were optimized in detail. Under the optimized conditions, the limits of detection (LODs) were found to be 0.003–0.06 μg kg⁻¹, and satisfactory recovery values of 84.8–103.1% were obtained for the tested seafood samples. It was confirmed that the developed method is simple, fast, sensitive, and accurate for the determination of 15 trace environmental phenols in seafood samples.     

Effective extraction of triazines from environmental water samples using magnetism-enhanced monolith-based in-tube solid phase microextraction

This article reports on the effective extraction of triazines from environmental water samples using magnetism-enhanced monolith-based in-tube solid phase microextraction (ME-MB/IT-SPME). Firstly, monolithic poly (octyl methacrylate-co-ethyleneglycol dimethacrylate) capillary column doped with magnetic nanoparticles was synthesized inside a fused silica. After that, the monolithic capillary column was placed inside a magnetic coil that allowed the exertion of a variable magnetic field during adsorption and desorption steps. The effects of intensity of magnetic field, adsorption and desorption flow rate, volume of sample and desorption solvent, pH value and ionic strength in sample matrix on the performance of ME-MB/IT-SPME for triazines were investigated in details. Under the optimized conditions, the developed ME-MB/IT-SPME showed satisfactory quantitative extraction efficiencies of the target analytes between 64.8% and 99.7%. At the same time, the ME-MB/IT-SPME was combined with high-performance liquid chromatography with diode array detection to detect six triazines in water samples. The limits of detection (S/N = 3) and limits of quantification (S/N = 10) were in the ranges of 0.074–0.23 μg/L and 0.24–0.68 μg/L, respectively. The precision of the proposed method was evaluated in terms of intra- and inter-assay variability calculated as relative standard deviation, and it was found that the values were all below 10%. Finally, the developed method was successfully applied for environmental water samples such as farmland, lake and river water with spiked recoveries in the range of 70.7–119%.     

Preparation of styrene-co-4-vinylpyridine magnetic polymer beads by microwave irradiation for analysis of trace 24-epibrassinolide in plant samples using high performance liquid chromatography

In the study, a kind of novel styrene-co-4-vinylpyridine (St-co-4-VP) porous magnetic polymer beads was prepared by microwave irradiation using suspension polymerization. Microwave heating preparation greatly reduced the polymerization time to 1 h. Physical characteristic tests suggested that these beads were cross-linking and possessed spherical shape, good magnetic response and porous morphologies with a narrow diameter distribution of 70–180 μm. Therefore, these beads displayed the long-term stability after undergoing 100-time extractions. Then, an analytical method for the determination of trace 24-epiBR in plant samples was developed by magnetic polymer bead extraction coupled with high performance liquid chromatography–fluorescence detection. St-co-4-VP magnetic polymer beads demonstrated the higher extraction selectivity for 24-epiBR than other reference compounds. Linear range was 10.00–100.0 μg/L with a relative standard deviation (RSD) of 6.7%, and the detection limit was 6.5 μg/kg. This analytical method was successfully applied to analyze the trace 24-epiBR in cole and breaking-wall rape pollen samples with recoveries of 77.2–90.0% and 72.3–83.4%, respectively, and RSDs were less than 4.1%. The amount of 24-epiBR in real breaking-wall rape pollen samples was found to be 26.2 μg/kg finally. This work proposed a sensitive, rapid, reliable and convenient analytical method for the determination of trace brassinosteroids in complicated plant samples by the use of St-co-4-VP magnetic polymer bead extraction coupled with chromatographic method.     

Stir bar sorptive-dispersive microextraction mediated by magnetic nanoparticles–nylon 6 composite for the extraction of hydrophilic organic compounds in aqueous media

A new and sensitive analytical method based on the recently developed approach termed stir bar-sorptive dispersive microextraction (SBSDME) using a magnetic CoFe₂O₄@SiO₂–nylon 6 composite as sorbent material is presented for the extraction of hydrophilic organic compounds. The simultaneous determination of four hydrophilic UV filters in environmental water samples has been chosen as a model analytical application due to the increasing awareness regarding the occurrence of sunscreen residuals in natural waters. The developed SBSDME approach combines the principles and benefits of stir bar sorptive extraction (SBSE) and dispersive solid phase extraction (DSPE) but allows for lower extraction time and easier post-extraction treatment. Moreover, most importantly, it enables the use of new magnetic materials that affords higher versatility and can be tailored to the needs of the analysis. The main experimental parameters involved in the SBSDME process (i.e. composite amount, extraction time, pH, ionic strength, desorption solvent and desorption time) were evaluated to provide the best enrichment factors. Under the optimized conditions, the method was successfully validated showing good linearity, enrichment factors between 105 and 145 depending on the analyte, limits of detection and quantification in the low ng mL⁻¹ range (1.6–2.9 ng mL⁻¹ and 5.4–9.6 ng mL⁻¹, respectively) and good intra- and inter-day repeatability (RSD < 13%). The developed method was applied to the analysis of water samples of different origin (sea, river and swimming pool). Relative recovery values ranged between 90 and 115%, thus showing that the matrices under consideration do not affect the extraction process.     

Development of a novel mixed hemimicelles dispersive micro solid phase extraction using 1-hexadecyl-3-methylimidazolium bromide coated magnetic graphene for the separation and preconcentration of fluoxetine in different matrices before its determination by fiber optic linear array spectrophotometry and mode-mismatched thermal lens spectroscopy

This study aims at developing a novel, sensitive, fast, simple and convenient method for separation and preconcentration of trace amounts of fluoxetine before its spectrophotometric determination. The method is based on combination of magnetic mixed hemimicelles solid phase extraction and dispersive micro solid phase extraction using 1-hexadecyl-3-methylimidazolium bromide coated magnetic graphene as a sorbent. The magnetic graphene was synthesized by a simple coprecipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The retained analyte was eluted using a 100 μL mixture of methanol/acetic acid (9:1) and converted into fluoxetine-β-cyclodextrin inclusion complex. The analyte was then quantified by fiber optic linear array spectrophotometry as well as mode-mismatched thermal lens spectroscopy (TLS). The factors affecting the separation, preconcentration and determination of fluoxetine were investigated and optimized. With a 50 mL sample and under optimized conditions using the spectrophotometry technique, the method exhibited a linear dynamic range of 0.4–60.0 μg L⁻¹, a detection limit of 0.21 μg L⁻¹, an enrichment factor of 167, and a relative standard deviation of 2.1% and 3.8% (n = 6) at 60 μg L⁻¹ level of fluoxetine for intra- and inter-day analyses, respectively. However, with thermal lens spectrometry and a sample volume of 10 mL, the method exhibited a linear dynamic range of 0.05–300 μg L⁻¹, a detection limit of 0.016 μg L⁻¹ and a relative standard deviation of 3.8% and 5.6% (n = 6) at 60 μg L⁻¹ level of fluoxetine for intra- and inter-day analyses, respectively. The method was successfully applied to determine fluoxetine in pharmaceutical formulation, human urine and environmental water samples.     

Microwave‐assisted preparation of poly(ionic liquids)‐modified polystyrene magnetic nanospheres for phthalate esters extraction from beverages

The fabrication of novel poly(ionic liquids)‐modified polystyrene (PSt) magnetic nanospheres (PILs‐PMNPs) by a one‐pot miniemulsion copolymerization reaction was achieved through an efficient microwave‐assisted synthesis method. The morphology, structure, and magnetic behavior of the as‐prepared magnetic materials were characterized by using transmission electron microscopy, vibrating sample magnetometry, etc. The magnetic materials were utilized as sorbents for the extraction of phthalate esters (PAEs) from beverage samples followed by high‐performance ultrafast liquid chromatography analysis. Significant extraction parameters that could affect the extraction efficiencies were investigated particularly. Under optimum conditions, good linearity was obtained in the concentration range of 0.5–50 (dimethyl phthalate), 0.3–50 (diethyl phthalate), 0.2–50 (butyl benzyl phthalate), and 0.4–50 μg/L (di‐n‐butyl phthalate), with correlation coefficients R ² > 0.9989. Limits of detection were in the range 125–350 pg. The proposed method was successfully applied to determine PAEs from beverage samples with satisfactory recovery ranging from 77.8 to 102.1% and relative standard deviations ranging from 3.7 to 8.4%. Comparisons of extraction efficiency with PSt‐modified MNPs as sorbents were performed. The results demonstrated that PILs‐PMNPs possessed an excellent adsorption capability toward the trace PAE analytes.     

Metal-organic framework-templated synthesis of magnetic nanoporous carbon as an efficient absorbent for enrichment of phenylurea herbicides

Nanoporous carbon with a high specific surface area and unique porous structure represents an attractive material as an adsorbent in analytical chemistry. In this study, a magnetic nanoporous carbon (MNC) was fabricated by direct carbonization of Co-based metal-organic framework in nitrogen atmosphere without using any additional carbon precursors. The MNC was used as an effective magnetic adsorbent for the extraction and enrichment of some phenylurea herbicides (monuron, isoproturon, diuron and buturon) in grape and bitter gourd samples prior to their determination by high performance liquid chromatography with ultraviolet detection. Several important experimental parameters that could influence the extraction efficiency were investigated and optimized. Under the optimum conditions, a good linearity was achieved in the concentration range of 1.0–100.0 ng g⁻¹ for monuron, diuron and buturon and 1.5–100.0 ng g⁻¹ for isoproturon with the correlation coefficients (r) larger than 0.9964. The limits of detection (S/N = 3) of the method were in the range from 0.17 to 0.46 ng g⁻¹. The results indicated that the MNC material was stable and efficient adsorbent for the magnetic solid-phase extraction of phenylurea herbicides and would have a great application potential for the extraction and preconcentration of more organic pollutants from real samples.     

One-step synthesis of agarose coated magnetic nanoparticles and their application in the solid phase extraction of Pd(II) using a new magnetic field agitation device

A magnetic solid phase extraction method based on agarose coated magnetic nanoparticles)ACMNPs(coupled to a new magnetic field agitation (MFA) device was developed and investigated for the separation, preconcentration and determination of Pd(II) in aqueous solutions. For the first time, the formation of the nanoparticles and their encapsulation in agarose micro-flakes was conducted in a single step. For this purpose, preparation of the magnetic iron oxide nanoparticles was performed in an alkaline agarose solution. The sizes of Fe₃O₄ nanoparticles and agarose micro-flakes were 10–14 nm and 90–130 μm, respectively. The nanomagnetic agarose particles were functionalized by iminodiacetic acid and subjected to magnetic field agitation in the MFA device. The influence of different analytical parameters such as pH, ionic strength, type and volume of desorption solvent and amount of the adsorbent on the preconcentration of Pd(II) were investigated. Eight replicated analysis at the optimized conditions, resulted in a recovery of 94.1% with an RSD of 5.2% for Pd(II). The detection limit of the method (3σ) was 47 ng L⁻¹ for the analyte. The method was successfully applied to the determination of Pd(II) in natural water samples.     

Use of magnetic effervescent tablet-assisted ionic liquid dispersive liquid–liquid microextraction to extract fungicides from environmental waters with the aid of experimental design methodology

In this work, a novel effervescence-assisted microextraction technique was proposed for the detection of four fungicides. This method combines ionic liquid-based dispersive liquid–liquid microextraction with the magnetic retrieval of the extractant. A magnetic effervescent tablet composed of Fe₃O₄ magnetic nanoparticles, sodium carbonate, sodium dihydrogen phosphate and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonimide) was used for extractant dispersion and retrieval. The main factors affecting the extraction efficiency were screened by a Plackett–Burman design and optimized by a central composite design. Under the optimum conditions, good linearity was obtained for all analytes in pure water model and real water samples. Just for the pure water, the recoveries were between 84.6% and 112.8%, the limits of detection were between 0.02 and 0.10 μg L⁻¹ and the intra-day precision and inter-day precision both are lower than 4.9%. This optimized method was successfully applied in the analysis of four fungicides (azoxystrobin, triazolone, cyprodinil, trifloxystrobin) in environmental water samples and the recoveries ranged between 70.7% and 105%. The procedure promising to be a time-saving, environmentally friendly, and efficient field sampling technique.     

Facile synthesis of multifunctional attapulgite/Fe3O4/polyaniline nanocomposites for magnetic dispersive solid phase extraction of benzoylurea insecticides in environmental water samples

In this study, the superparamagnetic attapulgite/Fe₃O₄/polyaniline (ATP/Fe₃O₄/PANI) nanocomposites were successfully synthesized by a one-pot method. Fe (III) was applied as both the oxidant for the oxidative polymerization of aniline and the single iron source of Fe₃O₄ formed by the redox reaction between aniline and Fe (III). The ATP/Fe₃O₄/PANI was used as sorbent for magnetic dispersive solid phase extraction (MDSPE) of benzoylurea insecticides (BUs) in environmental water samples. The as-prepared nanocomposite sorbents were characterized by Fourier transform infrared spectra (FT-IR), X Ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry. Various experimental parameters affecting the ATP/Fe₃O₄/PANI-based MDSPE procedure, including the composition of the nanocomposite sorbents, amount of ATP/Fe₃O₄/PANI nanocomposites, vortex time, pH, and desorption conditions were investigated. Under the optimal conditions, a good linearity was observed for all target analytes, with correlation coefficients (r²) ranging from 0.9985 to 0.9997; the limits of detection (LOD) were in the range of 0.02–0.43 μg L⁻¹, and the recoveries of analytes using the proposed method ranged between 77.37% and 103.69%. The sorbents exhibited an excellent reproducibility in the range of 1.52–5.27% in extracting the five target analytes. In addition, the intra-day and inter-day precision values were found to be in the range of 0.78–6.86% and 1.66–8.41%, respectively. Finally, the proposed ATP/Fe₃O₄/PANI-based MDSPE method was successfully applied to analyze river water samples by rapid preconcentration of BUs.     

Determination of organophosphorus pesticides by gas chromatography with mass spectrometry using a large‐volume injection technique after magnetic extraction

A fast and efficient method was developed for the extraction and determination of organophosphorus pesticides in water samples. Organophosphorus pesticides were extracted by solid‐phase extraction using magnetic multi‐walled carbon nanotubes and determined by gas chromatography with ion‐trap mass spectrometry. Parameters affecting the extraction were investigated. Under optimum conditions of the method, 10 mg magnetic multi‐walled carbon nanotubes were added into 10 mL sample. After 2 min, adsorbent particles settled at the bottom of test tube with a magnet. After removing aqueous supernatant, the analytes were desorbed with acetonitrile. Then, 70 μL of acetonitrile phase was injected into the gas chromatography and mass spectrometry system that had an ion‐trap analyzer. To achieve high sensitivity, the large‐volume‐injection technique was used with a programmed temperature vaporization inlet, and the ion‐trap mass spectrometer was operated in single ion storage mode. Under the best conditions, the enrichment factors and extraction recoveries were in the range of 113–124 and 74–103%, respectively. The limits of detection were between 3 and 15 ng/L, and the relative standard deviations were < 10%. This method was successfully used for the determination of organophosphorus pesticides in dam water, lagoon water, and river water samples with good reproducibility and recovery.     

Magnetic solid-phase extraction of sulfonylurea herbicides in environmental water samples by Fe3O4@dioctadecyl dimethyl ammonium chloride@silica magnetic particles

A magnetic solid phase extraction (MSPE) method coupled with high-performance liquid chromatography (HPLC) was proposed for the determination of five sulfonylurea herbicides (bensulfuron-methyl, prosulfuron, pyrazosulfuron-ethyl, chlorimuron-ethyl and triflusulfuron-methyl) in environmental water samples. The magnetic adsorbent was prepared by incorporating Fe₃O₄ nanoparticles and surfactant into a silica matrix according to a sol–gel procedure, which can provide surfactant free extracts during the eluting step to avoid chromatographic interference. The prepared adsorbent was used to extract the sulfonylurea herbicides in several kinds of water samples. The main factors affecting the extraction efficiency, including desorption conditions, extraction time, sample volume, and sample solution pH were optimized. Under the optimum conditions, good linearity was obtained within the range of 0.2–50.0 μg L⁻¹ for all analytes, with correlation coefficients ranging from 0.9993 to 0.9999. The enrichment factors were between 1200 and 1410, and the limits of detection were between 0.078 and 0.10 μg L⁻¹. The proposed method was successfully applied in the analysis of sulfonylurea herbicides in environmental samples (tap, reservoir, river, and rice field). The recoveries of the method ranged between 80.4% and 107.1%. This study reported for the first time the use of MSPE procedure in the preconcentration of sulfonylurea herbicides in environmental samples. The procedure proved to be efficient, environmentally friendly, and fast.     

Magnetic polyethyleneimine functionalized reduced graphene oxide as a novel magnetic solid-phase extraction adsorbent for the determination of polar acidic herbicides in rice

A novel magnetic polyethyleneimine modified reduced graphene oxide (Fe₃O₄@PEI-RGO) had been fabricated based on a self-assemble approach between positive charged magnetic polyethyleneimine (Fe₃O₄@PEI) and negative charged GO sheets via electrostatic interaction followed by chemical reduction of GO to RGO. The as-prepared Fe₃O₄@PEI-RGO was characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), thermal gravimetric analyzer (TGA), vibrating sample magnetometer (VSM) and zeta potential analysis, and then was successfully applied to determine four phenoxy acid herbicides and dicamba in rice coupled with high performance liquid chromatography (HPLC). As a surface modifier of RGO, PEI not only effectually affected the surface property of RGO (e.g. zeta potential), but also changed the polarity of RGO and offered anion exchange groups to polar acidic herbicides, which would directly influence the type of adsorbed analytes. Compared with Fe₃O₄@PEI, Fe₃O₄/RGO and Fe₃O₄@PEI-GO, the as-prepared Fe₃O₄@PEI-RGO, integrating the superiority of PEI and RGO, showed higher extraction efficiency for polar acidic herbicides. Besides, the adsorption mechanism was investigated as well. It turned out that electrostatic interaction and π-π interaction were considered to be two major driving force for the adsorption process. Response surface methodology (RSM), a multivariate experimental design technique, was used to optimize experimental parameters affecting the extraction efficiency in detail. Under the optimal conditions, a satisfactory performance was obtained. The calibration curves were linear over the concentration ranging from 2 to 300 ng g⁻¹ with correlation coefficients (r) between 0.9985 and 0.9994. The limits of detection (LODs) were in the range of 0.67–2 ng g⁻¹. The recoveries ranged from 87.41% to 102.52% with relative standard deviations (RSDs) less than 8.94%. Taken together, the proposed method was an efficient pretreatment and enrichment procedure and could be successfully applied for selective extraction and determination of polar acidic herbicides in complex matrices.     

Development of continuous dispersive liquid–liquid microextraction performed in home-made device for extraction and preconcentration of aryloxyphenoxy-propionate herbicides from aqueous samples followed by gas chromatography–flame ionization detection

In this study, a rapid, simple, and efficient sample preparation method based on continuous dispersive liquid–liquid microextraction has been developed for the extraction and preconcentration of aryloxyphenoxy-propionate herbicides from aqueous samples prior to their analysis by gas chromatography–flame ionization detection. In this method, two parallel glass tubes with different diameters are connected with a teflon stopcock and used as an extraction device. A mixture of disperser and extraction solvents is transferred into one side (narrow tube) of the extraction device and an aqueous phase containing the analytes is filled into the other side (wide tube). Then the stopcock is opened and the mixture of disperser and extraction solvents mixes with the aqueous phase. By this action, the extraction solvent is dispersed continuously as fine droplets into the aqueous sample and the target analytes are extracted into the fine droplets of the extraction solvent. The fine droplets move up through the aqueous phase due to its low density compared to aqueous phase and collect on the surface of the aqueous phase as an organic layer. Finally an aliquot of the organic phase is removed and injected into the separation system for analysis. Several parameters that can affect extraction efficiency including type and volume of extraction and disperser solvents, sample pH, and ionic strength were investigated and optimized. Under the optimum extraction conditions, the extraction recoveries and enrichment factors ranged from 49 to 74% and 1633 to 2466, respectively. Relative standard deviations were in the ranges of 3–6% (n = 6, C = 30 μg L⁻¹) for intra-day and 4–7% (n = 4, C = 30 μg L⁻¹) for inter-day precisions. The limits of detection were in the range of 0.20–0.86 μg L⁻¹. Finally the proposed method was successfully applied to determine the target herbicides in fruit juice and vegetable samples.     

Towards metals analysis using corona discharge ionization ion mobility spectrometry

For the first time, the capability of corona discharge ionization ion mobility spectrometry (CD-IMS) in the determination of metal complex was evaluated. The extreme simplicity of dispersive liquid–liquid microextraction (DLLME) coupled to the high sensitivity of CD-IMS measurement could make this combination really useful for simple, rapid, and sensitive determination of metals in different samples. In this regard, mercury, as a model metal, was complexed with diethyldithiocarbamate (DEDTC), and then extracted into the carbon tetrachloride using DLLME. Some parameters affecting the extraction efficiency, including the type and volume of the extraction solvent, the type and volume of the disperser solvent, the concentration of the chelating agent, salt addition and, pH were exhaustively investigated. Under the optimized condition, the enrichment factor was obtained to be 142. The linear range of 0.035–10.0 μg mL⁻¹ with r² = 0.997 and the detection limit of 0.010 μg mL⁻¹ were obtained. The relative standard deviation values were calculated to be lower than 4% and 8% for intra-day and inter-day, respectively. Finally, the developed method was successfully applied for the extraction and determination of mercury in various real samples. The satisfactory results revealed the capability of the proposed method in trace analysis without tedious derivatization or hydride generation.     

Simultaneous determination of four sedative-hypnotics in human urine based on dendritic structured magnetic nanomaterials

A magnetic solid-phase extraction technique based on magnetic dendritic structured nanoparticles (Fe₃O₄@SiO₂-NH₂-G5) as adsorbent coupled with ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) has been developed to detect diazepam, midazolam, zolpidem, and zaleplon in human urine. With Fe₃O₄@SiO₂-NH₂ as the central core, dendrimer (G5) grafted alternately with cyanuric chloride and imidazole were bonded to the surface of the core to synthesize Fe₃O₄@SiO₂-NH₂-G5. The morphology and structure of the magnetic materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and dynamic light scattering (DLS). The key parameters affecting the extraction efficiency were optimized. A satisfactory performance was obtained under the optimum extraction conditions. The proposed method was validated, and the limits of detection of zaleplon, diazepam, zolpidem, and midazolam were 0.05, 0.05, 0.02, and 0.02 ng mL^?1, respectively. The linear correlation coefficients r of the four analytes were > 0.996, the intra-day precision was between 2.4 % and 9.4 % with the recoveries between 88.3 % and 104.8 %, and the inter-day precision ranged from 3.9 % to 15.2 % with the recovery in the range of 94.1 %?108.3 %. The magnetic dendritic structure nanomaterial Fe₃O₄@SiO₂-NH₂-G5 was successfully used to extract sedative-hypnotic drugs from human urine samples. The Fe₃O₄@SiO₂-NH₂-G5-based magnetic solid-phase extraction method eliminates centrifugation and filtration steps as in conventional extraction. Only one step of vortex dispersion extraction could achieve the separation and purification of the target compounds. The proposed method was simple, rapid, environment-friendly, and suitable for the analysis of sedative-hypnotic drugs in human urine.     

pH-controlled quaternary ammonium herbicides capture/release by carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents: Mechanisms and application

In our work, the pH-controlled magnetic solid phase extraction for the determination of paraquat and diquat was introduced firstly. Furthermore, to clarify the mechanism of carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents, we studied the pH-responsive supramolecular interaction between carboxymethyl-β-cyclodextrin (CM-β-CD) and paraquat/diquat by ultraviolet–visible (UV–vis) spectroscopy and nuclear magnetic resonance (NMR) experiment, and the energy-minimized structures were also obtained. Then, the functional group CM-β-CD was modified on the surface of magnetic materials to synthesize the adsorbent. The Fourier transform infrared spectrum (FT-IR) results proved the successful modification of CM-β-CD. Thus, this absorbent was applied for the determination of paraquat and diquat in water. Under the optimal condition, limits of detection (LODs) of paraquat and diquat were 0.8 μg L⁻¹ and 0.9 μg L⁻¹, relative standard deviations (RSD) and recoveries varied 0.7–4.6% and 86.5–106.6%, respectively. Good recoveries (70.2–100.0%) and low RSD (1.7–9.6%) were achieved in analyzing spiked water samples. Furthermore, with the capillary electrophoresis (CE) as the analyser, the whole analytical process did not need the attendance of organic solvents.