Adsorption of asphaltene from crude oil by applying polythiophene coating on Fe3O4 nanoparticles

The objective of the present study was to investigate the potential use of applying polythiophene coating on magnetic Fe₃O₄ nanoparticles for the enhancement of asphaltene adsorption. Two stages of experimental were conducted. In the first stage, the ability of coated nanoparticles for asphaltene adsorption in synthetic asphaltene-toluene solution was evaluated. The effects of parameters such as nanoparticles concentration, initial concentration of asphaltene, and temperature were studied. In the second stage, the performance of the coated nanoparticles for the adsorption of asphaltene from crude oil was investigated under atmospheric pressure and a pressure-volume-temperature (PVT) apparatus was utilized for simulated reservoir conditions. Fe₃O₄ and Fe₃O₄-PT MNPs were synthesized using an effective co-precipitation method. The results of the first-stage tests indicated that the maximum adsorption capacity values for Fe₃O₄ and Fe₃O₄-PT MNPs were 0.79 and 1.09?mg?m^?2, respectively. The optimum value of nanoparticles concentration was approximately determined as 10?g?L^?1. According to the adsorption isotherms and kinetics, the Langmuir and pseudo-second-order Lagergren models were consistent with the experimental data, respectively. The average adsorption efficiencies for Fe₃O₄-PT and Fe₃O₄ MNPs were 78.98 and 65.94%, respectively. The results of the performed experiments on crude oil showed that Fe₃O₄-PT MNPs could adsorb asphaltenes from crude oil in a similar trend as synthetic asphaltene-toluene solution.     

Magnetic solid-phase extraction of Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.     

A rapid microwave-assisted acid extraction method based on the use of diluted HNO3-H2O2 followed by ICP-MS analysis for simultaneous determination of trace elements in coal samples

Before coal processing such as pyrolysis, liquefaction, gasification and combustion, it is very crucial to monitor the trace element concentration levels as that determines the coal quality. Therefore, the current study describes the development of microwave-assisted acid extraction (MW-AAE) method for extraction of 15 trace elements in coal samples prior to their determination using inductively coupled plasma-mass spectrometry. Diluted HNO₃-H₂O₂ was used in order to reduce reagents amount used, eliminate matrix interferences caused by concentrated acids and to decrease waste produced in analytical laboratories. The optimisation of the proposed extraction method was carried out by using a full factorial design (2⁴) involving four factors; that is, temperature, extraction time, HNO₃ and H₂O₂ concentrations. The optimum conditions for the MW-AAE procedure were found to be 200°C, 5 min, 5 mol L^?1 and 2 mol L^?1 for temperature, extraction time, HNO₃ and H₂O₂ concentrations, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and recoveries of 80–115% were achieved for V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Zr, Cs, Ba, Pb and U, except for Ti (10–25%) and Hf (27–70%). In addition, the precision of the proposed method, expressed in terms of relative standard deviation (SD) (n = 15), was within the accepted range (≤3.5%). The method detection limits of 0.001–0.57 µg g^?1 for all trace elements under the investigation were similar to the literature reported work, except for Ti (4.00 µg g^?1).     

Optimized solid phase extraction based on diethyldithiocarbamate-coated Fe3O4 magnetic nanoparticles followed by ICP-OES for determination of Cd(II) and Ni(II) in rice and water samples

In the present study, application of Fe₃O₄ magnetic nanoparticles (MNPs) coated with diethyldithiocarbamate as a solid-phase sorbent for extraction of trace amounts of cadmium (Cd²⁺) and nickel (Ni²⁺) ions by the aid of ultrasound was investigated. The analytes were determined by inductively coupled plasma-optical emission spectroscopy. Fe₃O₄ MNPs were prepared by solvothermal method and characterized with dynamic light scattering, scanning electron microscope and X-ray diffraction. Response surface methodology was used for optimization of the extraction process and modeling the data. The optimal conditions obtained were as follows: chelating agent, 1.2 g L^?1; pH, 6.13; sonication time, 13 min and Fe₃O₄ MNPs, 10.3 mg. The calibration curves were linear over the concentration range of 1–1,000 μg L^?1 for Cd²⁺ and 2.5–1,000 for Ni²⁺ with the determination coefficients (R ²) of 0.9997 and 0.9995, respectively. The limits of detection were 0.27 μg L^?1 for Cd²⁺ and 0.76 μg L^?1 for Ni²⁺. The relative standard deviations (n = 7, C = 200 μg L^?1) for determination of Cd²⁺ and Ni²⁺ were 2.0 and 2.7 %, respectively. The relative recoveries of the analytes from tap, river and lagoon waters and rice samples at the spiking level of 10 μg L^?1 were obtained in the range of 95–105 %.     

Chemiluminescent Determination of Vitamin B12 Using Charge Coupled Device (CCD)

A method was developed for the determination of vitamin B₁₂ based on the enhancement of cobalt (II) on the chemiluminescence (CL) reaction between luminol and percarbonate (powerful source of hydrogen peroxide). The release of cobalt (II) from the vitamin B₁₂ was reached by a simple and fast microwave digestion (20 s microwave digestion time and a mix of nitric acid and hydrogen peroxide). A charge coupled device (CCD) photodetector, directly connected to the cell, coupled with a simple continuous flow system was used to obtain the full spectral characteristics of cobalt (II) catalyzed luminol-percarbonate reaction.

The optima experimental conditions were established: 8.0 m mol L^?1 luminol in a 0.075 mol L^?1 carbonate buffer (pH 10.0) and 0.15 mol L^?1 sodium percarbonate, in addition to others experimental parameters as 0.33 mL s^?1 flow rate and 2 s integration time, were the experimental conditions which proportionate the optimum CL emission intensity. The emission data were best fitted with a second-order calibration graph over the cobalt (II) concentration range from 4.00 to 300 µ g L^?1 (r² = 0.9990), with a detection limit of 0.42 µ g L^?1. The proposed method was successfully applied to the determination of vitamin B₁₂ in pharmaceuticals.     

Determination of trace amounts of nystatin in water and vaccine samples using sodium dodecyl sulfate-coated iron oxide magnetic nanoparticles followed by high-performance liquid chromatography–ultraviolet detection

In this work, magnetic solid-phase extraction based on sodium dodecyl sulfate-coated Fe₃O₄ nanoparticles has been successfully applied for extraction and preconcentration of trace amounts of nystatin from water and vaccine samples prior to high-performance liquid chromatography–ultraviolet detection. Various experimental parameters affecting extraction and recovery of the analyte, such as the amount of sodium dodecyl sulfate, pH of the sample solution, salt concentration, extraction time, sample volume and desorption conditions, were systematically studied and optimized. Under optimized conditions, nystatin was quantitatively extracted. Proper linear range with good coefficient of determination, (R ² > 0.99) and limit of detection and quantification (based on signal-to-noise ratios of 3 and 10) of 2.0 and 5.0 µg L^?1, over the investigated concentration range (5–700 µg L^?1), were obtained, respectively. The intra-day and inter-day relative standard deviations at 50 µg L^?1 level of NYS were 1.4 and 4.5% based on six replicate determinations. The accuracy of the method was evaluated by recovery measurements on spiked samples. Suitable recoveries of 96–102 and 26–44% were achieved (at spiked levels of 50, 300 and 500 µg L^?1) for water and vaccine samples, respectively.     

Determination of Hydrogen Peroxide Using a Novel Sensor Based on Fe3O4 Magnetic Nanoparticles

Fe₃O₄ magnetic nanoparticles were synthesized by chemical co-precipitation with sodium citrate as a surfactant and were used with chitosan to construct a novel hydrogen peroxide sensor. The electrochemical behavior of hydrogen peroxide at the sensor was investigated by cyclic voltammetry. The composite film electrocatalyzed the reduction of hydrogen peroxide, and the peak current increased linearly with concentration from 1.00 × 10^?5 to 1.00 × 10^?3 mol · L^?1 (R = 0.9974) with a detection limit of 1.53 × 10^?6 mol · L^?1. This novel nonenzyme sensor provided good sensitivity, stability, and precision with potential applications.     

Magnetic solid-phase extraction based on Fe3O4/graphene oxide nanoparticles for the determination of malachite green and crystal violet in environmental water samples by HPLC

This work describes a magnetic Fe₃O₄/graphene oxide (GO)-based solid-phase extraction (MSPE) technique for high performance liquid chromatography (HPLC) detection of malachite green (MG) and crystal violet (CV) in environmental water samples. Fe₃O₄/ GO magnetic nanoparticles were synthesised by a chemical co-precipitation method and characterised by scanning electron micrograph, transmission electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface area analyser. The prepared Fe₃O₄/GO magnetic nanoparticles were used as the adsorbents of MSPE for MG and CV. By coupling with HPLC, a sensitive and cost-effective method for simultaneous determination of MG and CV was developed. The important parameters including the amount of Fe₃O₄/GO, pH of the sample solution, extraction time, salt effect, the type and volume of desorption solvent were investigated in detail. Under optimised conditions, the calibration curves were linear in the concentration range of 0.5–200 μg L^?1, and the limits of detection were 0.091 and 0.12 μg L^?1 for MG and CV, respectively. Finally, the established MSPE-HPLC method was successfully applied to determine MG and CV in environmental water samples with the recoveries ranging from 91.5% to116.7%.     

Determination of Veterinary Pharmaceuticals in Production Wastewater by HPTLC-Videodensitometry

An SPE-HPTLC method for simultaneous identification and quantification of seven pharmaceuticals in production wastewater was optimized and validated. The studied compounds were enrofloxacine, oxytetracycline, trimethoprim, sulfamethazine, sulfadiazine, sulfaguanidine and penicillin G/procaine. The method involves solid-phase extraction on hydrophilic-lipophilic balance cartridges with methanol and HPTLC analysis of extracts on CN modified chromatographic plates followed by videodensitometry at 254 and 366 nm. Optimization of chromatographic separation was performed by systematic variation of the mobile phase composition using genetic algorithm approach and the optimum mobile phase composition for TLC separation was 0.05 M H₂C₂O₄:methanol = 0.81:0.19 (v/v). Linearity of the method was demonstrated in the ranges from 1.5 to 15.0 μg L⁻¹ for enrofloxacine, 100–500 μg L⁻¹ for oxytetracycline, 150–600 μg L⁻¹ for trimethoprim, 300–1100 μg L⁻¹ for sulfaguanidine and 100–400 μg L⁻¹ for sulfamethazine, sulfadiazine and penicillin G/procaine with coefficients of determination higher than 0.991. Mean recoveries ranged from 74.6 to 117.1% and 55.1 to 108.0% for wellspring water and production wastewater, respectively. Only sulfaguanidine showed lower results. The described method has been applied to the determination of pharmaceuticals in wastewater samples from pharmaceutical industry.     

Determination of Cadmium in Fruit and Vegetables by Ionic Liquid Magnetic Microextraction and Flame Atomic Absorption Spectrometry

An ionic liquid-linked dual magnetic microextraction procedure is reported for cadmium(II) with flame atomic absorption spectrometry. Cadmium was complexed with pyrolidine dithiocarbamate and the chelate was extracted into the fine droplets of 1-butyl-3-methylimidazolium hexafluorophosphate by using a vortex mixer with Fe₃O₄ nanoparticles. Plackett–Burman design was used to optimize relevant parameters of the method, including the pH, the volume of ionic liquid, the amount of ammonium pyrolidine dithiocarbamate, the mass of magnetic nanoparticles, and the vortex time. The pH, volume of ionic liquid, and mass of ammonium pyrolidine dithiocarbamate significantly affected the recovery. The limit of detection, preconcentration factor, and relative standard deviation were 0.32 µg L^?1, 80, and 3.4%, respectively. The procedure was validated by the analysis of spinach leaves standard reference material 1570a and recovery measurements. Practical application of the method involved the determination of cadmium in fruit and vegetables.     

Determination of Tetracycline in Water and Honey by Iron(II,III)/Aptamer-Based Magnetic Solid-Phase Extraction with High-Performance Liquid Chromatography Analysis

A novel aptamer-based adsorbent was prepared for the magnetic solid-phase extraction of tetracycline. The Fe₃O₄/aptamer adsorbent was fabricated by immobilizing an aptamer on the surface of Fe₃O₄ magnetic nanoparticles by the reaction between avidin and biotin. The parameters affecting the isolation efficiency such as the pH, extraction time, extraction temperature, eluent, and elution time were investigated in detail. Under the optimal conditions, a linear relationship between the peak area and the concentration of tetracycline was observed in the range from 10.0 to 3000.0?µg L^?1 with a correlation coefficient of 0.9985 and a limit of detection of 2.5?µg L^?1. The developed method was successfully employed for the determination of tetracycline in honey and water samples with recovery values from 82.9 to 107.3% and relative standard deviations less than 7.6%. Compared with previously reported methods for the determination of tetracycline, the proposed protocol provides improvements in the limit of detection and specificity with reduced consumption of adsorbent and organic solvents.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@ionic liquid-β-cyclodextrin polymer magnetic solid phase extraction coupled with HPLC for the separation/analysis of congo red

Fe₃O₄@ionic liquids β-cyclodextrin polymer(Fe₃O₄@mono-6-deoxy-6-(1-ethyl-imidazolium)-β-cyclodextrin iodide polymer, Fe₃O₄@ILs-β-CDCP) was prepared. Magnetic solid phase extraction coupled with high-performance liquid chromatography for the separation/analysis of congo red (CR) in water and drysaltery was established. Fe₃O₄@ILs-β-CDCP showed a higher adsorption capacity toward CR. CR was adsorbed rapidly by Fe₃O₄@ILs-β-CDCP (adsorption efficiency: 95%) and eluted by ethanol (elution efficiency: 96%) at room temperature. Under the optimal conditions, preconcentration factor of the proposed method was 20-fold. The linear range, correlation coefficient (R ²), detection limit (DL) and relative standard deviation were found to be 0.005–100.00 µg mL^?1, 0.9910, 1.8 g L^?1 and 0.61% (n = 3, c = 5.00 µg mL^?1), respectively. The adsorption mechanism of CR on Fe₃O₄@ILs-β-CDCP was studied through the FTIR analysis. The accuracy of the developed method was confirmed by spiking city water, lake water, pond water and drysaltery. Fe₃O₄@ILs-β-CDCP can be used repeatedly for 10 times. This proposed method had been successfully applied to the determination of CR in real samples.     

Square-Wave Anodic Stripping Voltammetry (SWASV) for the Determination of Ecotoxic Metals,Using a Bismuth-Film Electrode

This article reviews the use of square wave anodic stripping voltammetry for the simultaneous determination of ecotoxic metals (Pb, Cd, Cu, and Zn) on a bismuth-film (BiFE) electrode. The BiFE was prepared in situ on a glassy-carbon electrode (GCE) from the 0.1 mol L^?1 acetate buffer solution (pH 4.5) containing 200 µg L^?1 of bismuth (III). The addition of hydrogen peroxide to the electroanalytical cell proved beneficial for the interference-free determination of Cu (II) together with zinc, lead, and cadmium, using the BiFE. The experimental variables were investigated and optimized with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. The performance characteristics, such as reproducibility, decision limit (CC_a), detection capability (CC_β), sensitivity, and accuracy indicated that the method holds promise for trace Cu²⁺, Pb²⁺, Cd²⁺, and Zn²⁺ levels by employment of Hg-free GCE with SWASV. CCa, and CCβ were calculated according to the Commission Decision of 12 August 2002 (2002/657/EC). Linearity was observed in the range 20–280 µg L^?1 for zinc, 10–100 µg L^?1 for lead, 10–80 µg L^?1 for copper, and 5–50 µg L^?1 for cadmium. Using the optimized conditions, the stripping performance of the BiFE was characterized by low limits of detection (LOD). Finally, the method was successfully applied in real as well as in certified reference water samples.     

Facile synthesis of Fe3O4/MoS2 nanohybrid for solid phase extraction of Ag(I) and Pb(II): kinetic,isotherm and thermodynamic studies

Recently, MoS₂ with abundant electron density in its structure attracted more attention as an adsorbent for environmental remediation. However, hard manipulation of target solution owing to high dispersibility in aqueous media restricts its application as adsorbent. Preparation of Fe₃O₄/MoS₂ nanohybrid can solve this problem. Also, this nanohybrid improves adsorption capacities of target ions. In this work, Fe₃O₄ nanoparticles, MoS₂ nanosheets and hybrid of these two were synthesised and then characterised by X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Fourier transforms infrared spectra, Brunauer–Emmett–Teller surface area and vibrating sample magnetometer. Subsequently, adsorption of Ag(I) and Pb(II) ions from aqueous solution by these three adsorbents was examined in detail and compared with each other while the adsorption conditions including the pH value, contact time, dosage of sorbent, elution conditions and interfering ions have been optimised. According to obtained results, prepared nanohybrid showed enhanced adsorption capacities for both ions relative to naked Fe₃O₄ and MoS₂. The limits of detection for Ag(I) and Pb(II) were calculated as 0.49 µg L^?1 and 2.7 µg L^?1, respectively, and the relative standard deviation percentages (n = 5) for Ag(I) and Pb(II) were 2.8%, and 3.0%, respectively. Furthermore, the preconcentration factors were 300 and 75 for Ag(I) and Pb(II) ions, respectively. Moreover, kinetic studies showed that pseudo-second-order model can better describe target analytes adsorption properties by every three adsorbents. Regeneration of the adsorbents was performed with HCl/thiourea mixture.     

Polythiophene-coated Fe3O4 nanoparticles as a selective adsorbent for magnetic solid-phase extraction of silver(I), gold(III), copper(II) and palladium(II)

We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe₃O₄ magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L^?1 concentration range (R²?>?0.998), limits of detection in the range from 0.2 to 2.0 μg L^?1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.

Synthesis of 2-mercaptobenzothiazole/magnetic nanoparticles modified multi-walled carbon nanotubes for simultaneous solid-phase microextraction of cadmium and lead

This study describes the successful sequential modification of multi-walled carbon nanotube (MWCNT) by Fe₃O₄ magnetic nanoparticles and 2-mercaptobenzothiazole (MBT) followed by its application as a novel sorbent for simultaneous magnetic solid phase microextraction of lead and cadmium. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the chemical surface modification of the MWCNT. The ions retained on the 2-MBT/magnetic nanoparticles modified MWCNTs were eluted with 1.0 mL of nitric acid (0.8 mol L^?1) in methanol solution and determined by the flame atomic absorption spectrometry. All parameters affecting the extraction condition were thoroughly investigated and optimised. Under the optimised condition preconcentration factor of 150.0, enhancement factors of 149.0 and 149.2 and limits of detection of 0.21 and 0.01 µg L^?1 were achieved for lead and cadmium, respectively. Using the prepared magnetic nanocomposite, the possible interference of other common ions associated with lead and cadmium determination was effectively avoided and the method was successfully applied to the simultaneous determination of the target ions in various environmental water samples.     

Custom-Made C18 Column for Simultaneous Determination of Endocrine Disrupting Substances in Water by Diode-Array and Fluorescence Detectors

A C₁₈ stationary phase was synthesized for a custom-made HPLC column. When compared to a commercial C₁₈ column, better chromatographic performances were obtained. This column was successfully applied for simultaneous determination of p,p′-DDT, o,p′-DDT, benzo(a)anthracene, benzo(b)fluoranthene, and benzo(a)pyrene in waters by high performance liquid chromatography coupled with dual detectors (diode array and fluorescence detectors) combined with solid phase extraction. Low method detection limits were obtained, i.e., p,p′-DDT: 0.5 µg L^?1, o,p′-DDT: 1 µg L^?1, benzo(a)anthracene: 2.5 ng L^?1, benzo(b)fluoranthene: 5 ng L^?1, and benzo(a)pyrene: 2.5 ng L^?1. High recoveries that ranged from 82 to 94% were obtained for all compounds.     

Ion Chromatography with Post-column Reaction and Serial Conductivity and Spectrophotometric Detection Method Development for Quantification of Transition Metal Dissolution in Lithium Ion Battery Electrolytes

We present a method for the separation and determination of transition metals in electrolytes based on ion chromatography (IC) with post-column reaction (PCR) and serial conductivity and spectrophotometric detection. Three IC columns [Metrosep C4—250/4.0 (column A), Metrosep C6—250/4.0 (column B), and Nucleosil 100-5SA—250/4.6 (column C)] with different capacities, and stationary phases were used and compared with each other for method development. All spectrophotometric measurements were carried out with 4-(2-pyridylazo)resorcinol (PAR) as PCR reagent at a wavelength of 500 nm. To characterize the precision of the separation, the selectivity for the analysis of transition metals (nickel, cobalt, copper, and manganese) in the presence of large amounts of lithium and the resolution of the peaks were determined and compared with one another. Furthermore, the limits of detection (LOD) and quantification (LOQ) were determined for the transition metals. The LODs and LOQs determined by column C were as follows: cobalt (LOD/LOQ): 9.4 µg L^?1/31.3 µg L^?1, manganese (LOD/LOQ): 7.0 µg L^?1/23.5 µg L^?1, and nickel (LOD/LOQ): 6.3 µg L^?1/21.1 µg L^?1. Finally, the concentration of transition metal dissolution of the cathode material Li₁Ni_1/3Co_1/3Mn_1/3O₂ (NCM) was investigated for different charge cut-off voltages by the developed IC method.     

Simple Method for Determination of Lead in Hair Dyes Using Slurry Sampling Graphite Furnace Atomic Absorption Spectrometry

A fast, simple and sensitive method for determining of lead in hair dyes using graphite furnace atomic absorption spectrometry with slurry sampling was developed. Multivariate optimization was used to establish optimal analytical parameters through a fractional factorial and a central composite design. The samples were submitted for direct analysis without prior digestion and were diluted in 2.5% v/v HNO₃ and 1.5% v/v H₂O₂. Palladium (chemical modifier) and rhodium (permanent modifier) were selected from several potential modifiers. The optimal conditions were a pyrolysis time of 10 s (liquid and dust dyes) 20 s (cream dyes), a pyrolysis temperature of 789°C (liquid dyes) or 750°C (cream and dust dyes) and an atomization temperature of 1800°C for all dyes. Under optimum conditions, the calibration graph is linear in the 1.50–50.0 µg L^?1 concentration range, with a detection limit of 0.33, 0.44, and 0.39 µg L^?1 for liquid, dust, and cream hair dyes, respectively. The relative standard deviation ranged from 1.63 to 4.56%. The recovery rate ranged from 85 to 108%, and no significant differences were found between the results obtained with the proposed method and the microwave decomposition analysis method of real samples. The concentration ranges obtained for lead in the hair dyes samples were 1.00–11.3 µg L^?1 for liquid dyes, 14.0–100 µg kg^?1 for dust dyes, and 19.9–187 µg kg^?1 for cream dyes.     

Molecularly imprinted stir bar sorptive extraction coupled with high-performance liquid chromatography for trace analysis of naphthalene sulfonates in seawater

In this paper, a novel molecularly imprinted polymer coated stir bar has been used to selectively extract naphthalene sulfonates (NS_s) directly from seawater sample. 1-Naphthalene sulfonic acid (1-NS) was used as template molecule. The effects of different parameters were optimized on the extraction efficiency and the optimum conditions were established as: the absorption and desorption times were fixed, respectively, at 10 and 15 min, stirring speed was 700 rpm, pH was adjusted to 4.1, amount of NaCl was 1 mol L^?1 and extraction process was performed at a temperature of 50 °C. The linear ranges were 2–250 µg L^?1 for 3,6-NDS-1-OH (1-naphthol-3,6-disulfonic acid), 4–250 µg L^?1 for 2-NS (2-naphthalene sulfonate) and 3–250 µg L^?1 for 1-NS. The detection limits were within the range of 0.32–0.95 µg L^?1. Under optimum conditions, the detection limits of the NSs were 0.84, 0.95 and 0.32 µg L^?1 with the enrichment factor of 117-, 41- and 77-fold for 2-NS, 1-NS, and 6-NDS-1-OH, respectively. The repeatability of the method was satisfactory (0.53 ≤ RSD ≤6.0 %, n = 10). The method has been successfully applied for the analysis of trace amounts of three naphthalene sulfonates in seawater of Chabahar Bay.