Continuous flow liquid membrane extraction: a novel automatic trace-enrichment technique based on continuous flow liquid-liquid extraction combined with supported liquid membrane

Combining the continuous flow liquid-liquid extraction (CFLLE) and supported liquid membrane (SLM) extraction, a novel aqueous-aqueous extraction technique that we termed continuous flow liquid membrane extraction (CFLME) is developed for trace-enrichment. The analyte was firstly extracted into the organic phase in the CFLLE step, then transported onto the organic liquid membrane that formed on the surface of the micro porous membrane of the SLM equipment. Finally, it passed through the liquid membrane and was trapped by the acceptor. Aspects related to CFLME were studied by using dichloromethane as liquid membrane, and sulfonylurea herbicides as model compounds. An enrichment factor of over 1000 was obtained when 10 μg l⁻¹ of MSM was enriched for 120 min by this technique. The drawbacks of only a few organic solvents can be selected as liquid membrane with a limited lifetime in SLM operation was overcome. In this CFLME method, almost all solvents that used in the conventional liquid-liquid extraction (LLE) can be adopted and the lifetime of liquid membrane is no longer a problem.     

Evaluation of an on-line coupled continuous flow liquid membrane extraction and precolumn system as trace enrichment technique by liquid chromatographic determination of bisphenol A

An on-line coupled continuous flow liquid membrane extraction (CFLME) and C₁₈ precolumn system was developed for sample preconcentration in liquid chromatography determination. After preconcentration by CFLME, which is based on the combination of continuous flow liquid–liquid extraction and supported liquid membrane, bisphenol A (BPA) was enriched in 960 μl of 1 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto a C₁₈ analytical column for separation and detected at 220 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor, and enrichment time were optimized. The proposed method presents a detection limit of 0.03 μg l⁻¹ (S/N=3) when 60 ml samples was enriched with an enrichment time of 30 min. Compared with C₁₈ based column-switching procedure, this proposed procedure presents similar sample throughput and lower detection limits. The proposed method was successfully applied to determine BPA in tap water, river water, and municipal sewage effluent samples.     

Use of Nb(2)O(5)-SiO(2) in an automated on-line preconcentration system for determination of copper and cadmium by FAAS

A procedure for the determination of trace level of copper(II) and cadmium(II) by FAAS using an on-line preconcentration system has been proposed. In this system, copper and cadmium ions were adsorbed onto a minicolumn packed with silica gel modified with niobium(V) oxide (Nb₂O₅-SiO₂), followed by nitric acid elution in reverse mode and determination on-line by flame atomic absorption spectrometry (AAS) without interference of the matrix. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. The enrichment factor for copper(II) and cadmium(II) was 34.2 and 33.0, respectively, using a preconcentration time of 2 min. The limit of detection for copper(II) and cadmium(II) was 0.4, and 0.1 μg l⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation in solutions containing 15 μg l⁻¹ of copper and 10 μg l⁻¹ of cadmium, by analyzing a series of seven replicates, was 1.8 and 1.6%, respectively. The accuracy was assessed through recovery experiments of certified material and water samples.     

Trace analysis of sulfonylurea herbicides in water by on-line continuous flow liquid membrane extraction--C18 precolumn liquid chromatography with ultraviolet absorbance detection

An on-line system that consists of continuous-flow liquid membrane extraction (CFLME), C18 precolumn, and liquid chromatography with UV detection was applied to trace analysis of sulfonylurea herbicides in water. During preconcentration by CFLME, five target compounds, including metsulfuron methyl, bensulfuron methyl, tribenuron methyl, sulfometuron methyl, and ethametsulfuron, were enriched in 960 microl of 0.5 mol l(-1) Na2CO3-NaHCO3 (pH 10.8) buffer used as acceptor. This acceptor was on-line neutralized and transported to the C18 precolumn where the analytes were absorbed and focused. Then the focused analytes were injected onto a C18 analytical column for separation and detection at 240 nm. The proposed method was applied to determine sulfonylurea herbicides in water, river, and reservoir water with detection limits of 10-50 ng l(-1) when enriching a 120-ml sample. Throughput is typically one sample per hour.     

Determination of trace elements in natural waters by inductively coupled plasma time of flight mass spectrometry after flow injection preconcentration in a knotted reactor

A flow injection on-line sorption system was developed for the separation and preconcentration of traces of Ag, Cd, Co, Ni, Pb, U and Y from natural water samples with subsequent detection by ICP TOF MS. Simultaneous preconcentration of the analytes was achieved by complexation with the chelating reagent 1-phenyl-3-methyl-4-benzoylpyrazol-5-one immobilized on the inner walls of a (200 cm × 0.5 mm) PTFE knotted reactor. The analytes were eluted and transported to an axial ICP TOF MS system with 1% (v/v) HNO₃ containing 0.3 μg l⁻¹ of Rh as an internal standard using ultrasonic nebulization. The detection limits (3σ) varied from 0.3 ng l⁻¹ for Y to 15.2 ng l⁻¹ for Ni and the precision (R.S.D.) was better than 4%. Using a loading time of 90 s and a sample flow rate of 4.5 ml min⁻¹, enhancement factors of 3-14 were obtained for the different analytes in comparison with their direct determination by ICP TOF MS with ultrasonic nebulization without preconcentration. The accuracy of the method was demonstrated by analysis of water based certified reference materials.     

Interfacing in-line gas-diffusion separation with optrode sorptive preconcentration exploiting multisyringe flow injection analysis

An automatic multisyringe flow injection analysis (MSFIA) system coupling a flow-through optical fiber diffuse reflectance sensor with in-line gas-diffusion (GD) separation is proposed for the isolation, preconcentration and determination of traces of volatile and gas-evolving compounds in samples containing suspended solids, with no need for any preliminary batch sample treatment. The flowing methodology overcomes the lost of sensitivity of the in-line separation technique, when performed in a uni-directional continuous-flow mode, through the implementation of disk-based solid-phase extraction schemes. The high selectivity and sensitivity, the low reagent consumption and the miniaturization of the whole assembly are the outstanding features of the automated set-up. The proposed combination of techniques for separation, flow analysis, preconcentration and detection was applied satisfactorily to sulfide determination in environmental complex matrixes. The method based on multicommutation flow analysis involves the stripping of the analyte as hydrogen sulfide from the donor channel of the GD-module into an alkaline receiver segment, whereupon the enriched plug merges with well-defined zones of the chormogenic reagents (viz., N,N-dimethyl-p-phenylenediamine (DMPD) and Fe(III)). The in-line generated methylene blue dye is subsequently delivered downstream to the dedicated optrode cell furnished with a C₁₈ disk, while recording continuously the diffuse reflectance spectrum of the pre-concentrated compound. This procedure provides a linear working range of 20-500 μg l⁻¹ sulfide with a relative standard deviation of 2.2% (n = 10) at the 200 μg l⁻¹ level, and a detection limit of 1.3 μg l⁻¹.     

Development of an on-line preconcentration system for zinc determination in biological samples

An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythrocyte matrices by flame atomic absorption spectrometry (FAAS) was used. This procedure was based on adsorption of Zn(II) ions onto a minicolumn filled with silica gel, chemically modified with niobium(V) oxide (Nb₂O₅-SiO₂). The determination of the optimum conditions for Zn(II) preconcentration was done using two-level full factorial and Doehlert designs. In the optimization procedure, four variables (sample pH, eluent concentration, sample flow rate and eluent flow rate) were investigated. The results obtained from the full factorial design demonstrated that the sample pH and sample flow rate variables, and their interactions, were statistically significant. A Doehlert matrix was used in order to determine the optimum conditions for the sample pH and sample flow rate. The optimized conditions for sample pH and flow rate sampling were 6.6 and 7.1 ml min⁻¹, respectively, to obtain the maximum Zn(II) preconcentration and determination in the biological samples studied. Parameters of analytical curve, precision, effect of other ions in the proposed system and accuracy were achieved to assess the proposed method. The accuracy was confirmed by analysis of certified reference materials (urine Seronorm™ Trace Elements) and recovery tests in blood plasma and erythrocyte samples. Detection limit (3σ/S) of 0.77 μg l⁻¹, precision (calculated as relative standard deviation) of 1.5% for Zn(II) concentration of 10 μg l⁻¹ (n = 7) and a sampling frequency of 27 samples/h were obtained from the proposed system.     

Simultaneous determination of sex hormones in egg products by ZnCl2 depositing lipid, solid-phase extraction and ultra performance liquid chromatography/electrospray ionization tandem mass spectrometry

A method was developed for simultaneous determination of residues of 17 sex hormones in egg products. Target compounds were extracted from samples with methanol in an ultrasonic bath, effectively separated from lipids in the extracts by ZnCl₂ depositing filtration and purified using a C₁₈ solid-phase extraction (SPE) and followed by NH₂ SPE cartridge. The analytes were quantified by liquid chromatography using a BEH C₁₈ column coupled to an electrospray ionization tandem mass spectrometer (LC-ESI-MS/MS) operating in negative mode for estrogens and in positive multiple reaction monitoring mode for androgens. The parameters of the mass spectrometer and the composition of mobile phase and additives were also optimized to enhance detection sensitivity. Average recoveries of the target compounds varied from 70.0% to 121.0% with relative standard deviations ranging from 2.3% to 11.2% at two fortification levels. The limits of detection (LOD) of the method were from 0.002 μg kg⁻¹ to 0.23 μg kg⁻¹ and the limits of quantification (LOQ) were in the range of 0.007-0.76 μg kg⁻¹.     

Mixed hemimicelles solid-phase extraction of chlorophenols in environmental water samples with 1-hexadecyl-3-methylimidazolium bromide-coated Fe3O4 magnetic nanoparticles with high-performance liquid chromatographic analysis

In this paper, 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr)-coated Fe₃O₄ magnetic nanoparticles (NPs) as an adsorbent of mixed hemimicelles solid-phase extraction was investigated for the preconcentration of two chlorophenols (CPs) in environmental water samples prior to HPLC with UV detection at 285 nm. The high surface area and excellent adsorption capacity of the Fe₃O₄ NPs after modification with C₁₆mimBr were utilized adequately in the SPE process. By the rapid isolation of Fe₃O₄ NPs through placing a strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conventional SPE method with a column can be avoided. A comprehensive study of the adsorption conditions such as the zeta-potential of Fe₃O₄ NPs, added amounts of C₁₆mimBr, pH value, standing time and maximal extraction volume were also presented. Under optimized conditions, two analytes of 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were quantitatively determined. The method was then used to determine the two CPs in real environmental water samples. The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (74–90%) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the two CPs were obtained with only a small amount of Fe₃O₄ NPs (40 mg) and C₁₆mimBr (24 mg).     

Sulphoxine immobilized onto chitosan microspheres by spray drying: application for metal ions preconcentration by flow injection analysis

A new chelating resin based on chitosan biopolymer modified with 5-sulphonic acid 8-hydroxyquinoline using the spray drying technique for immobilization is proposed. The chelating resin was characterized by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) and surface area by nitrogen sorption. The efficiency of the chelating resin was evaluated by the preconcentration of metal ions Cu(II) and Cd(II) present in aqueous samples in trace amounts. The metal ions were previously enriched in a minicolumn and the concentrations of the analytes were determined on-line by flame atomic absorption spectrometry (FAAS). The maximum retention for Cu(II) occurred in the pH range 8-10, and for Cd(II) at pH 7. The optimum flow rate for sorption was found to be 7.2 ml min⁻¹ for the preconcentration of the metal ions. The analytes gave relative standard deviations (R.S.D.) of 0.7 and 0.6% for solutions containing 20 μg l⁻¹ of Cu(II) and 15 μg l⁻¹ of Cd (II), respectively (n=7). The enrichment factors for Cu(II) and Cd (II) were 19.1 and 13.9, respectively, and the limits of detection (LOD) were 0.2 μg l⁻¹ for Cd(II) and 0.3 μg l⁻¹ for Cu(II), using a preconcentration time of 90 s (n=11). The accuracy of the proposed method was evaluated by the metal ion recovery technique, in the analysis of potable water and water from a lake, with recoveries being between 97.2 and 107.3%.     

Inorganic/organic mesoporous silica as a novel fiber coating of solid-phase microextraction

Mesoporous materials were employed as fast, sensitive and efficient fiber coatings of solid-phase microextraction (SPME) for the first time. Three micrometer as-synthesized C₁₆-MCM-41 particles were immobilized onto stainless steel wire with 100 μm coating thickness. In combination with high performance liquid chromatography (HPLC), extraction efficiency and selectivity of C₁₆-MCM-41 were investigated using aromatic hydrocarbons. Effect of extraction and desorption time, extraction temperature, stirring rate and ionic strength on extraction efficiency were examined. Aanalytical merits of SPME with C₁₆-MCM-41 coating were evaluated. The chromatographic peak area is proportional to the concentration of anthracene in the range 0.5-150 μg l⁻¹. The limit of detection was 0.05 μg l⁻¹ (S/N=3) and the relative standard deviation (R.S.D.) was 0.033%.     

Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP-FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0 ml min⁻¹ and a total preconcentration time of 180 s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26 μg l⁻¹ for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2 μg l⁻¹ Cr(VI), Co(II) and Ni(II), and 1 μg l⁻¹ Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.     

Chelating resin from functionalization of chitosan with complexing agent 8-hydroxyquinoline: application for metal ions on line preconcentration system

This study describes the functionalization of biopolymer chitosan, using the complexing agent 8-hydroxyquinoline (oxine) by reaction of diazotization. The chelating resin was characterized by degree of deacetylation, infrared, Raman spectroscopy. The efficiency of the chelating resin and accuracy of the proposed method was evaluated by the metal ion recovery technique in the analysis of potable water, lake water, seawater and a certified sample of oyster tissue. The metal ions Cd(II) and Cu(II) in the samples were previously enriched in a minicolumn and flow injection flame atomic absorption spectrometry (FI-FAAS) determined the concentrations of the analytes. The chelating resin exhibited high selectivity for Cd(II) at pH 7 and for Cu(II) at pH 10. The eluent concentration was tested by the use of HNO₃ in concentrations of 0.1-3 mol l⁻¹ maximum response was obtained at 0.5 mol l⁻¹ for Cd(II) and Cu(II), with R.S.D. values of 0.4%. The analytes gave relative standard deviations (R.S.D.) of 1.5 and 0.7% for solutions of Cd(II) and Cu(II), respectively (n = 7) containing 20 μg l⁻¹ of the metal ions, defining a high reproducibility. The limits of detection (LOD) were 0.1 μg l⁻¹ for Cd(II) and 0.4 μg l⁻¹ for Cu(II). The analytical properties of merit were obtained using the parameters previously optimized with preconcentration time of 90 s. The chelating resin showed chemical stability within a wide range of pH and the efficiency was not altered for the preconcentration of the metal ions during all the experiments.     

High speed liquid chromatography for in-process control of rifabutin

A fast HPLC method has been developed for simultaneous determination of rifabutin and its synthesis precursors. The analytes are separated in 1.8 min by means of a Kromasil 100 C₁₈ column (50 mm × 2.1 mm i.d., 3.5 μm) at 30 °C. The mobile phase (A: 5 mM KH₂PO₄ adjusted to pH 6.5 with KOH; B: acetonitrile) was pumped at a flow rate of 0.4 ml min⁻¹ according to the fast gradient mode: 0 min, 58% B; 0-0.4 min, 95% B. Detection was by ultraviolet absorbance at 275 nm. The method was validated in accordance with the International Conference on Harmonisation (ICH) guidelines and good accuracy, intermediate precision (≤4.6%) and linearity in the range 5-50 mg l⁻¹ were observed for all compounds. This method is sensitive (limits of detection ranged between 0.1 and 0.3 mg l⁻¹) and selective to quantify rifabutin and its synthesis precursors and could be used for in-process control.     

A permeation liquid membrane system for determination of nickel in seawater

The use of a permeation liquid membrane system for the preconcentration and separation of nickel in natural and sea waters and subsequent determination by atomic absorption spectroscopy is presented. 2-Hydroxybenzaldehyde N-ethylthiosemi-carbazone (2-HBET) in toluene is used as the active component of the liquid membrane. A study strategy based on a simplex design has been followed. Several chemical and physical parameters were optimized. Maximum permeation coefficient was obtained at a feed solution pH of 9.4, 0.3 mol l⁻¹ of HNO₃ in the stripping solution and 1.66 mmol l⁻¹ of 2-HBTE in toluene as carrier. The precision of the method was 4.7% at 95% significance level and a detection limit of 0.012 μg l⁻¹ of nickel was achieved. The preconcentration procedure showed a linear response within the studied concentration range from 3 to 500 μg l⁻¹ of Ni in the feed solution. The method was validated with different spiked synthetic seawater and certified reference water samples: TMDA-62 and LGC 6016, without matrix interferences and showing good concordance with the certified values, being the relative errors −5.9% and −2.2%, respectively. Under optimal conditions, the average preconcentration yield for real seawater samples was 98 ± 5%, with a nickel preconcentration factor of 20.83 and metal concentrations ranging between 2.8 and 5.4 μg l⁻¹.     

Determination of chlorophenols in landfill leachate using headspace sampling with ionic liquid-coated solid-phase microextraction fibers combined with gas chromatography–mass spectrometry

A new microextraction technique based on ionic liquid solid-phase microextraction (IL-SPME) was developed for determination of trace chlorophenols (CPs) in landfill leachate. The synthesized ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), was coated onto the spent fiber of SPME for extraction of trace CPs. After extraction, the absorbed analytes were desorbed and quantified using gas chromatography–mass spectrometry (GC/MS). The term of the proposed method is as ionic liquid-coated of solid-phase microextraction combined with gas chromatography–mass spectrometry (IL-SPME-GC/MS). No carryover effect was found, and every laboratory-made ionic liquids-coated-fiber could be used for extraction at least eighty times without degradation of efficiency. The chlorophenols studied were 2,4-dichlorophenol (2,4-DP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP). The best results of chlorophenols analysis were obtained with landfill leachate at pH 2, headspace extraction for 4 min, and thermal desorption with the gas chromatograph injector at 240 °C for 4 min. Linearity was observed from 0.1 to 1000 μg L⁻¹ with relative standard deviations (RSD) less than 7% and recoveries were over 87%. The limit of detection (LOD) for pentachlorophenol was 0.008 μg L⁻¹. The proposed method was tested by analyzing landfill leachate from a sewage farm. The concentrations of chlorophenols were detected to range from 1.1 to 1.4 μg L⁻¹. The results demonstrate that the IL-SPME-GC/MS method is highly effective in analyzing trace chlorophenols in landfill leachate.     

Optimization of temperature-controlled ionic liquid dispersive liquid phase microextraction combined with high performance liquid chromatography for analysis of chlorobenzenes in water samples

Temperature-controlled ionic liquid dispersive liquid phase microextraction (TCIL-DLPME) combined with high performance liquid chromatography-diode array detection (HPLC-DAD) was applied for preconcentration and determination of chlorobenzenes in well water samples. The proposed method used 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) as the extraction solvent. The effect of different variables on extraction efficiency was studied simultaneously using an experimental design. The variables of interest in the TCIL-DLPME were extraction solvent volume, salt effect, solution temperature, extraction time, centrifugation time, and heating time. The Plackett-Burman design was employed for screening to determine the variables significantly affecting the extraction efficiency. Then, the significant factors were optimized by using a central composite design (CCD) and the response surface equations were developed. The optimal experimental conditions obtained from this statistical evaluation included: extraction solvent volume, 75 μL; extraction time, 20 min; centrifugation time, 25 min; heating time, 4 min; solution temperature, 50 °C; and no addition of salt. Under optimal conditions, the preconcentration factors were between 187 and 298. The limit of detections (LODs) ranged from 0.05 μg L⁻¹ (for 1,2-dichlorobenzene) to 0.1 μg L⁻¹ (for 1,2,3-trichlorobenzene). Linear dynamic ranges (LDRs) of 0.5-300 and 0.5-500 μg L⁻¹ were obtained for dichloro- and trichlorobenzenes, respectively. The performance of the method was evaluated for extraction and determination of chlorobenzenes in well water samples in micrograms per liter and satisfactory results were obtained (RSDs < 9.2%).     

Determination of methylmercury and inorganic mercury in water samples by slurry sampling cold vapor atomic absorption spectrometry in a flow injection system after preconcentration on silica C18 modified

A novel method for preconcentration of methylmercury and inorganic mercury from water samples was developed involving the determination of ng l⁻¹ levels of analytes retained on the silica C₁₈ solid sorbent, previous complexation with ammonium pyrrolidine dithiocarbamate (APDC), by slurry sampling cold vapor atomic absorption spectrometry (SS-CVAAS) in a flow injection (FI) system. Several variables were optimized affecting either the retention of both mercury species, such as APDC concentration, silica C₁₈ amount, agitation times, or their determination, including hydrochloric acid concentration in the suspension medium, peristaltic pump speed and argon flow-rate. A Plackett-Burman saturated factorial design permitted to differentiate the influential parameters on the preconcentration efficiency, which were after optimized by the sequential simplex method. The contact time between mercury containing solution and APDC, required to reach an efficient sorption, was decreased from 26 to 3 min by the use of sonication stirring instead of magnetic stirring. The use of 1 mol dm⁻³ hydrochloric acid suspension medium and 0.75% (m/v) sodium borohydride reducing agent permitted the selective determination of methylmercury. The combination of 5 mol dm⁻³ hydrochloric acid and 10⁻⁴% (m/v) sodium borohydride was used for the selective determination of inorganic mercury. The detection limits achieved for methylmercury and inorganic mercury determination under optimum conditions were 0.96 and 0.25 ng l⁻¹, respectively. The reliability of the proposed method for the determination of both mercury species in waters was checked by the analysis of samples spiked with known concentrations of methylmercury and inorganic mercury; quantitative recoveries were obtained.     

Polythiophene-coated Fe3O4 superparamagnetic nanocomposite: Synthesis and application as a new sorbent for solid-phase extraction

In the present work, a novel type of superparamagnetic nanosorbent, polythiophene-coated Fe₃O₄ nanoparticles (Fe₃O₄@PTh NPs), have been successfully synthesized. The synthesized NPs were characterized by scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy, and thermal gravimetric analysis (TGA). The synthesized Fe₃O₄@PTh NPs were applied as an efficient sorbent for extraction and preconcentration of several typical plasticizer compounds (di-n-butyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), and dioctyl adipate (DOA)) from environmental water samples. Separation of Fe₃O₄@PTh NPs from the aqueous solution was simply achieved by applying external magnetic field. Separation and determination of the extracted plasticizers was performed by gas chromatography–flame ionization detection (GC–FID). Several variables affecting the extraction efficiency of the analytes i.e., amount of NPs sorbent, salt concentration, extraction time, and desorption conditions were investigated and optimized. The best working conditions were as follows: amount of sorbent, 100 mg; NaCl concentration, 30% (w/v); sample volume, 45 mL; extraction time, 10 min; and 100 μL of ethyl acetate for desorption of the analytes within 2 min. Under optimized conditions, preconcentration factors for DBP, DEHP, and DOA were obtained as 86, 194, and 213, respectively. The calibration curves were linear (R² > 0.998) in the concentration range of 0.4–100 μg L⁻¹ for both DEHP and DOA and 0.7–100 μg L⁻¹ for DBP. The limits of detection (LODs) were obtained in the range of 0.2–0.4 μg L⁻¹. The intra-day relative standard deviations (RSDs%) based on four replicates were obtained in the range of 4.0–12.3%. The proposed procedure was applied to analysis of water samples including river water, bottled mineral water, and boiling water exposed to polyethylene container (after cooling) and recoveries between 85 and 99% and RSDs lower than 12.8% were obtained.     

A new high-speed hollow fiber based liquid phase microextraction method using volatile organic solvent for determination of aromatic amines in environmental water samples prior to high-performance liquid chromatography

A new and fast hollow fiber based liquid phase microextraction (HF-LPME) method using volatile organic solvents coupled with high-performance liquid chromatography (HPLC) was developed for determination of aromatic amines in the environmental water samples. Analytes including 3-nitroaniline, 3-chloroaniline and 4-bromoaniline were extracted from 6 mL basic aqueous sample solution (donor phase, NaOH 1 mol L⁻¹) into the thin film of organic solvent that surrounded and impregnated the pores of the polypropylene hollow fiber wall (toluene, 20 μL), then back-extracted into the 6 μL acidified aqueous solution (acceptor phase, HCl 0.5 mol L⁻¹) in the lumen of the two-end sealed hollow fiber. After the extraction, 5 μL of the acceptor phase was withdrawn into the syringe and injected directly into the HPLC system for the analysis. The parameters influencing the extraction efficiency including the kind of organic solvent and its volume, composition of donor and acceptor phases and the volume ratio between them, extraction time, stirring rate, salt addition and the effect of the analyte complexation with 18-crown-6 ether were investigated and optimized. Under the optimal conditions (donor phase: 6 mL of 1 mol L⁻¹ NaOH with 10% NaCl; organic phase: 20 μL of toluene; acceptor phase: 6 μL of 0.5 mol L⁻¹ HCl and 600 m mol L⁻¹ 18-crown-6 ether; pre-extraction and back-extraction times: 75 s and 10 min, respectively; stirring rate: 800 rpm), the obtained EFs were between 259 and 674, dynamic linear ranges were 0.1-1000 μg L⁻¹ (R > 0.9991), and also the limits of detection were in the range of 0.01-0.1 μg L⁻¹. The proposed procedure worked very well for real environmental water samples with microgram per liter level of the analytes, and good relative recoveries (91-102%) were obtained for the spiked sample solutions.