Modified dispersive liquid-liquid microextraction for pre-concentration of benzene, toluene, ethylbenzene and xylenes prior to their determination by GC

We have developed a modified method for the extraction and preconcentration of benzene, toluene, ethylbenzene and xylenes (BTEX) in aqueous samples. It based on dispersive liquid-liquid microextraction along with solidification of floating organic microdrops. The dispersion of microvolumes of an extracting solvent into the aqueous occurs without dispersive solvent. Various parameters have been optimized. BTEX were quantified via GC with FID detection. Under optimized conditions, the preconcentration factors range from 301 to 514, extraction efficiencies from 60 to 103 %, repeatabilities from 2.2 to 4.1 %, and intermediate precisions from 3.5 to 7.0 %. The relative recovery for each analyte in water samples at three spiking levels is >85.6 %, with a relative standard deviation of <7.4 %.

Nano polypyrrole-coated magnetic solid phase extraction followed by dispersive liquid phase microextraction for trace determination of megestrol acetate and levonorgestrel

The aim of the present work is combination of the advantages of magnetic solid phase extraction (MSPE) and dispersive liquid phase microextraction (DLLME) followed by filtration-based phase separation. A new pretreatment method was developed for trace determination of megestrol acetate and levonorgestrel by liquid chromatography/ultraviolet detection in biological and wastewater samples. After magnetic solid phase extraction, the eluent of MSPE was used as the disperser solvent for DLLME. Emulsion resulted from DLLME procedure was passed through the in-line filter for phase separation. Finally the retained analytes in the filter was washed with mobile phase of liquid chromatography and transferred to the column for separation. This approach offers the preconcentration factors of 3680 and 3750 for megestrol acetate and levonorgestrel, respectively. This guarantees determination of the organic compounds at trace levels. The important parameters influencing the extraction efficiency were studied and optimized. Under the optimal extraction conditions, a linear range of 0.05–50 ng mL⁻¹ (R² > 0.998) and limit of detection of 0.03 ng mL⁻¹ were obtained for megestrol acetate and levonorgestrel. Under optimal conditions, the method was successfully applied for determination of target analytes in urine and wastewater samples and satisfactory results were obtained (RSDs < 6.8%).     

A bucky gel consisting of Fe3O4 nanoparticles,graphene oxide and ionic liquid as an efficient sorbent for extraction of heavy metal ions from water prior to their determination by ICP-OES

Microchimica Acta - Bucky gels are gelatinous composite materials consisting of carbon nanotubes and ionic liquids. The authors describe the synthesis of a bucky gel containing Fe3O4 nanoparticles...     

Selective determination of inorganic cobalt in nutritional supplements by ultrasound-assisted temperature-controlled ionic liquid dispersive liquid phase microextraction and electrothermal atomic absorption spectrometry

In the present work, a simple and rapid analytical method based on application of ionic liquids (ILs) for inorganic Co(II) species (iCo) microextraction in a variety of nutrient supplements was developed. Inorganic Co was initially chelated with 1-nitroso-2-naphtol (1N2N) reagent followed by a modern technique named ultrasound-assisted temperature-controlled ionic liquid dispersive liquid phase microextraction (USA-TILDLME). The extraction was performed with 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆mim][PF₆] with the aid of ultrasound to improve iCo recovery. Finally, the iCo-enriched IL phase was solubilized in methanol and directly injected into an electrothermal atomic absorption spectrometer (ETAAS). Several parameters that could influence iCo microextraction and detection were carefully studied. Since the main difficulty in these samples is caused by high concentrations of potential interfering ions, different approaches were evaluated to eliminate interferences. The limit of detection (LOD) was 5.4 ng L^?1, while the relative standard deviation (RSD) was 4.7% (at 0.5 μg L^?1 Co level and n = 10), calculated from the peak height of absorbance signals. Selective microextraction of iCo species was achieved only by controlling the pH value during the procedure. The method was thus successfully applied for determination of iCo species in nutritional supplements.     

A magnetic MoS2-Fe3O4 nanocomposite as an effective adsorbent for dispersive solid-phase microextraction of lead(II) and copper(II) prior to their determination by FAAS

Microchimica Acta - The authors describe the preparation of a nanocomposite (mag-MoS2-Fe3O4) that was prepared from molybdenum disulfide (MoS2) and magnetic Fe3O4 nanoparticles by a hydrothermal...     

Fe3O4-modified graphene oxide as a sorbent for sequential magnetic solid phase extraction and dispersive liquid phase microextraction of thallium

Microchimica Acta - A combination of magnetic solid phase extraction (MSPE) and dispersive liquid phase microextraction (DLPME) was applied in a new method for preconcentration and extremely...     

Simultaneous determination of cypermethrin and permethrin in pear juice by ultrasound-assisted dispersive liquid-liquid microextraction combined with gas chromatography

A new method was developed for simultaneous determination of cypermethrin and permethrin residues in pear juice with ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) and gas chromatography-flame ionization detection (GC-FID). 3.5 mL of methanol (dispersant) and 30 μL of C₂Cl₄ (extractant) were injected into 5.0 mL of pear juice sample and then emulsified by ultrasound for 2.0 min to forming the cloudy solution. Under the optimum condition, the enrichment factors for cypermethrin and permethrin were 344 and 351 fold respectively. Good linearity was observed in a range of 0.009-1.52 μg g⁻¹ with the correlation coefficient (r²)≥0.9993. The limits of detection (LODs) were 3.1 and 2.2 μg kg⁻¹ for cypermethrin and permethrin, respectively (S/N = 3). The recoveries of the method evaluated at three spiked levels were in the range of 92.1%-107.1%. The repeatability evaluated as intra-day and inter-day precision (RSDs) were less than 4.0% (n = 5). The developed method was successfully applied to determine the two pesticide residues in different pear juice samples.     

Ion pair-based dispersive liquid-liquid microextraction for gold determination at ppb level in solid samples after ultrasound-assisted extraction and in waters by electrothermal-atomic absorption spectrometry

A new methodology was developed for the determination of ultratrace levels of gold in water samples, soils and river sediments. Dispersive liquid-liquid microextraction was used to preconcentrate the ion pair formed between AuCl₄⁻ and [CH₃(CH₂)₃]₄N⁺ in a microliter-range volume of chlorobenzene using acetone as disperser solvent. When solid samples were analyzed, the method consisted of a combination of ultrasound-assisted extraction and dispersive liquid-liquid microextraction with final detection by electrothermal-atomic absorption spectrometry. Since an HCl medium was required for the formation of the AuCl₄⁻ complex, HCl together with HNO₃ was used as extractants for ultrasound-assisted extraction. After optimization, the enrichment factor obtained was 220 for water samples. Moreover, the extraction efficiency was around 96%. The repeatability, expressed as relative standard deviation ranged from 3.6% to 9.7%. The instrumental detection limit was 8.4 ng L⁻¹, whereas the procedural detection limits were 42 ng L⁻¹ for water samples and 1.5 ng g⁻¹ for environmental solid samples.     

Enrichment and sensitive determination of dichlorodiphenyltrichloroethane and its metabolites with temperature controlled ionic liquid dispersive liquid phase microextraction prior to high performance liquid phase chromatography

Dichlorodiphenyltrichloroethane (DDT) and its main metabolites are important environmental pollutants and have been in the focusing center. It is of great value to develop simple, rapid, sensitive and easy to operate method for monitoring them. Present work established a novel temperature controlled ionic liquid dispersive liquid phase microextraction method in combination with high performance liquid chromatography for the enrichment and determination of DDT and its metabolites. Proposed method used only ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) for the enrichment and overcame the demerits of conventional single drop liquid phase microextraction and dispersive liquid-liquid microextraction. Temperature has two functions here, one is to promote the dispersing of ionic liquid into the solution and forming infinitesimal micro-drop and increasing the chance of the analytes extracted into ionic liquid phase, and the other one is to perform phase-separation. A series of factors that would affect the extraction performance was systematically investigated and optimized. The experimental results indicated that the detection limits obtained for p,p′-DDD, p,p′-DDT, o,p′-DDT and p,p′-DDE were 0.24, 0.24, 0.45, 0.24 ng mL⁻¹, respectively. The linear ranges for them were from 1.0 to 100 ng mL⁻¹, and the precisions were between 3.8% and 6.7% (n = 6). The proposed method was validated with four real-world samples and excellent results were achieved.     

阴极等离子体电解法制备氧化铝纳米颗粒

以金属铝为阴极材料,以3mol·L-1浓度的NH4NO3水溶液为电解液,采用非对称电极阴极等离子体电解方法制备出氧化铝纳米颗粒.采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能量色散谱(EDX)、X射线衍射(XRD)和X射线光电子能谱(XPS)对颗粒的形貌和结构进行了表征.结果表明颗粒以立方相Al2O3为主.还对放电过程的电流变化和发光现象进行了研究.结合实验结果提出了这种颗粒的生长机制.     

A nanomagnetic and 3-mercaptopropyl-functionalized silica powder for dispersive solid phase extraction of Hg(II) prior to its determination by continuous-flow cold vapor AAS

Microchimica Acta - The authors describe a method for the trace determination of Hg(II) in human fluids using magnetic dispersive solid phase extraction. A silica powder magnetized with Fe3O4...     

Extraction optimization of polycyclic aromatic hydrocarbons by alcoholic-assisted dispersive liquid-liquid microextraction and their determination by HPLC

A sensitive method for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) using alcoholic-assisted dispersive liquid-liquid microextraction (AA-DLLME) and HPLC was developed. The extraction procedure was based on alcoholic solvents for both extraction and dispersive solvents. The effective parameters (type and volume of extraction and dispersive solvents, amount of salt and stirring time) on the extraction recovery were studied and optimized utilizing factorial design (FD) and central composite design (CCD). The best recovery was achieved by FD using 2-ethyl-1-hexanol as the extraction solvent and methanol as the dispersive solvent. The results showed that volume of dispersive solvent and stirring time had no effect on the recovery of PAHs. The optimized conditions were 145 μL of 2-ethyl-1-hexanol as the extraction solvent and 4.2% w/v of salt (NaCl) in sample solution. The enrichment factors of PAHs were in the range of 310-325 with limits of detection of 0.002-0.8 ng/mL. The linearity was 0.01-800 ng/mL for different PAHs. The relative standard deviation (RSD) for intra- and inter-day of extraction of PAHs were in the range of 1.7-7.0 and 5.6-7.3, respectively, for five measurements. The method was also successfully applied for the determination of PAHs in environmental water samples.     

Determination of geosmin and 2-methylisoborneol in water and wine samples by ultrasound-assisted dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A fast, simple and environmentally friendly ultrasound-assisted dispersive liquid–liquid microextraction (USADLLME) procedure has been developed to preconcentrate geosmin and 2-methylisoborneol (MIB) from water and wine samples prior to quantification by gas chromatography–mass spectrometry (GC–MS). A two-stage multivariate optimization approach was developed by means of a Plackett–Burman design for screening and selecting the significant variables involved in the USADLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were: solvent volume, 8 μL; solvent type: tetrachloroethylene; sample volume, 12 mL; centrifugation speed, 2300 rpm; extraction temperature 20 °C; extraction time, 3 min; and centrifugation time, 3 min. Under the optimized experimental conditions the method gave good levels of repeatability with coefficient of variation under 11% (n = 10). Limits of detection were 2 and 9 ng L⁻¹ for geosmin and MIB, respectively. Calculated calibration curves gave high levels of linearity with correlation coefficient values of 0.9988 and 0.9994 for geosmin and MIB, respectively. Finally, the proposed method was applied to the analysis of two water (reservoir and tap) samples and three wine (red, rose and white) samples. The samples were previously analyzed and confirmed free of target analytes. Recovery values ranged between 70 and 113% at two spiking levels (0.25 μg L⁻¹ and 30 ng L⁻¹) showing that the matrix had a negligible effect upon extraction. Only red wine showed a noticeable matrix effect (70–72% recovery). Similar conclusions have been obtained from an uncertainty budget evaluation study.     

HKUST-1 metal-organic framework for dispersive solid phase extraction of 2-methyl-4-chlorophenoxyacetic acid (MCPA) prior to its determination by ion mobility spectrometry

The authors describe a method for the extraction of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) from agricultural products. The metal organic framework (MOF) HKUST-1 (a copper(II) benzene-1,3,5-tricarboxylate) was used as a sorbent for efficient clean-up and preconcentration of MCPA. The effects of pH value, stirring time, amount of sorbent on extraction were optimized by central composite design. Ultrasonic waves were used for desorption procedure and its advantage was demonstrated for an increase in extraction recovery. Corona discharge ion mobility spectrometry (IMS) was then applied for fast and sensitive determination of MCPA. The method was validated in terms of sensitivity, recovery and reproducibility. Under the optimum conditions the calibration plot is linear between 0.035–0.200 μg. L^?1. The detection limit is 10 ng L^?1, with relative standard deviations of <5%. Real samples (water, soil and agricultural product) were spiked and then analyzed by this method, and the results revealed efficient solid phase extraction and recovery.

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Graphical abstract Schematic presentation of a procedure for extraction of an organochlorine pesticide (2-methyl-4-chlorophenoxyacetic acid) from agriculture products using the HKUST-1 metal-organic framework prior to determination by ion mobility spectrometry based on its ionization in drift cell.

     

Sensitive determination of carbamates in fruit and vegetables by a combination of solid-phase extraction and dispersive liquid-liquid microextraction prior to HPLC

We report on a new method for sample pretreatment. It is based on solid-phase extraction combined with dispersive liquid-liquid microextraction (SPE-DLLME) and was applied to the determination of carbamates in apple and cucumber. The carbamates carbofuran, carbaryl, and pirimicarb were first extracted from samples by SPE. The analytes were then eluted from the sorbent with acetonitrile, and the DLLME technique was then applied to the resulting eluate. Finally, the analytes in the extraction solvent were determined by HPLC. Several parameters affecting the SPE-DLLME process were optimized. The new method provides enrichment factors that range from 5,400 to 7,650. Calibration plots are linear in the range from 0.25 to 100?μg?kg^?1 for carbofuran and carbaryl, and from 0.10 to 100?μg?kg^?1 for pirimicarb, with correlation coefficient (r²) ranging from 0.9980 to 0.9997. The limits of detection range from 5 to 60?pg?kg^?1 (at S/N?=?3). The method was successfully applied to the extraction and sensitive determination of carbamates in apple and cucumber samples.

Preparation, characterization and application of KNH2/Al2O3 and KF/Al2O3 as strong solid bases

This review describes the preparation, characterization and application of KNH₂ loaded on alumina and KF loaded on alumina. These strong solid bases catalyze a variety of organic reactions in a very selective manner. The reactions include isomerizations of alkenes and alkynes, dimerization of alkynes, Tishchenko reaction, and the reaction of silanes to form of Si–C, Si–N and Si–O bonds.     

A poly-dopamine based metal-organic framework coating of the type PDA-MIL-53(Fe) for ultrasound-assisted solid-phase microextraction of polychlorinated biphenyls prior to their determination by GC-MS

The authors describe an ultrasonic-assisted headspace method for solid phase micro-extraction (UA-HS-SPME) of 7 polychlorinated biphenyls (PCBs) with codes PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180. The coating is based on a poly-dopamine metal-organic framework [PDA-MIL-53(Fe)] on a stainless steel wire. The coating can be prepared and evenly deposited on the stainless fiber by dipping the PDA fiber into a solution of MIL-53(Fe). The assay is also environmentally friendly because water is used as the solvent. The effects of extraction time, addition of salts, pH value and power of ultrasonic power were optimized. The coating is found to possess a high selectivity and adsorption capacity for PCBs compared to commercial SPME fibers such as the divinylbenzene/carboxen/polydimethylsiloxane fibers. Following desorption, the PCBs were quantified by GC-MS. The detection limits are between 50 and 90 pg?g^?1 of PCBs in soil. The fibers can be easily prepared, and the batch-to-batch reproducibility (RDS) is <10% (for n = 6). The fibers are inexpensive, re-usable and can be easily manipulated, and particularly well suited for screening polychlorinated biphenyls in soil.

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Graphical abstract Schematic of the preparation of an extraction fiber using stainless steel wire as substrate, PDA as adhesive, and MIL-53(Fe) as the adsorbent. It was applied to the extraction of PCBs from soil. The fiber is durable and inexpensive.