Trace analysis of Pt (IV) metal ions in roadside soil and water samples by Fe3O4/graphene/polypyrrole nanocomposite as a solid-phase extraction sorbent followed by atomic absorption spectrometry

A novel Fe₃O₄/graphene/polypyrrole nanocomposite has been successfully synthesised via a simple chemical method and applied as a new magnetic solid-phase extraction (MSPE) sorbent for the separation and pre-concentration of trace amounts of Pt (IV) in environmental samples followed by flame atomic absorption spectrometric (FAAS) detection. The nanocomposite has been characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Seven important parameters, affecting the extraction efficiency of Pt (IV), including pH, adsorption time, desorption solvent type and concentration, desorption time, elution volume and sample volume, were investigated. Under the optimised conditions, the calibration graph was linear in the range of 50–1500 μg L^?1 (R = 0.993). The detection limit and pre-concentration factor (PF) for Pt (IV) were found to be 16 μg L^?1 and 112.5, respectively. Under the optimised solid-phase extraction (SPE) conditions, the adsorption isotherm and the adsorption capacity of the nanocomposite for Pt (IV) were studied. Pt (IV) adsorption equilibrium data were fitted well to the Langmuir isotherm and the maximum adsorption capacity of the magnetic sorbent was calculated from the Langmuir isotherm model as 416.7 mg g^?1. The precision of the method was studied as intraday and interday variations. A relative standard deviation percentage (RSD%) value less than 3.0 indicates that the method is precise. Also, the accuracy of the method was tested by the analysis of the standard reference material (NIST SRM 2556) and by recovery measurements on spiked real samples. It was also shown that the optimised method was suitable for the analysis of trace amounts of Pt (IV) in roadside soil, tap water and wastewater samples.     

Trace determination of lead(II) ions by using a magnetic nanocomposite of the type Fe3O4/TiO2/PPy as a sorbent,and FAAS for quantitation

Microchimica Acta - The authors describe a magnetic nanoadsorbent consisting of magnetite nanoparticles coated first with titanium dioxide and then with polypyrrole (PPy). It is shown to be a...     

Magnetic nanocomposite of self‐doped polyaniline–graphene as a novel sorbent for solid‐phase extraction

This work is the first study on the extraction efficiency of self‐doped polyaniline that is immobilized on the graphene‐modified magnetic nanoparticles. The new material was used as a sorbent for the magnetic solid‐phase extraction of methyl‐, propyl‐, and butylparabens. The use of graphene provides a high surface area and prevents aggregation of the nanoparticles. The self‐doped polyaniline also provides multifunctionality, high extraction capacity, and chemical stability even in the basic medium. The parabens were acetylated for determination by gas chromatography with flame ionization detection. The effects of monomer ratio, extraction solvent, sorbent amount, sample volume, desorption solvent volume, adsorption and desorption times, and sample ionic strength were optimized. Preconcentration factors obtained were from 190 to 310. The detection limits of the method were <2.8 μg/L. Linear ranges of the method were 5–2000 μg/L for propyl and butyl parabens, and 10–2000 μg/L for methyl paraben. The method was applied for the determination of the parabens in cosmetic products and extraction recoveries were 89–101% with RSDs ≤7.9%.     

Polyimide‐coated magnetic nanoparticles as a sorbent in the solid‐phase extraction of polycyclic aromatic hydrocarbons in seawater samples

Magnetic polyimide poly(4,4′‐oxydiphenylene‐pyromellitimide) nanoparticles were successfully synthesized and developed for the solid‐phase extraction of polycyclic aromatic hydrocarbons in seawater samples. The aromatic rings of polyimide coating provided a good adsorption capacity (28.3–42.5 mg/g) for polycyclic aromatic hydrocarbons because of the π–π stacking interaction. The developed method was used as a simple, fast, and efficient extraction and preconcentration technique for the trace analysis of polycyclic aromatic hydrocarbons. The high chemical, physical and thermal stability, excellent reusability, and good magnetic properties are the merits of the sorbent. High preconcentration factors (41–63) were obtained. The sorbent was also characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X‐ray spectrometry, transmission electron microscopy, and vibrating sample magnetometry. After optimizing several appropriate extraction parameters, the results indicated that the extraction recoveries of polycyclic aromatic hydrocarbons were in the range of 61.6–94.7%, with relative standard deviations between 2.9 and 5.4%, the calibration graph was linear in the concentration range of 1–100 μg/L (r > 0.9991) with limit of detection in the range of 0.15–0.19 μg/L (n = 3). Seawater samples were analyzed as real samples and good recoveries (68.5–99.5%) were obtained at different spiked values.     

Preparation and evaluation of thermally stable nano-structured self-doped polythiophene coating for analysis of phthalate ester trace levels

Nano‐structured self‐doped polythiophene (SPT) electrodeposited in the presence of fluorinated organic acid was applied as a thermally stable conductive polymer‐based solid‐phase microextraction (SPME) fiber candidate. Quantitative determination of trace levels of phthalate esters including dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), and diethylhexyl phthalate (DEHP) was carried out using this novel fiber, coupling with gas chromatography‐flame ionization detector (GC‐FID). The SPT coating was proved to be stable at high temperatures (～350°C) with a high extraction capacity and long lifetime (more than 60 times). Improved temperature resistance was obtained by the presence of sulfonated groups in the backbone of polymer. Thermal stability of novel SPT was superior to common polythiophene (synthesized in LiClO₄). The extraction procedure was optimized by means of the Taguchi orthogonal array experimental design with an OA₁₆ (4⁵) matrix including extraction temperature, extraction time, salt concentration, stirring rate, and headspace volume. The good linearity was obtained for most compounds with correlation coefficients (R²) of between 0.993 and 0.995. The detection limits were lower than 0.12 ng/mL for dimethyl phthalate, DEP, dibutyl phthalate, and diethylhexyl phthalate. The method was successfully applied to the analysis of water samples with the recoveries from 90±1 to 107±1%.     

A cortisol nanocomposite-based electrochemical sensor for enantioselective recognition of mandelic acid

An electrochemical chiral sensor was designed based on graphene (GR) as a catalyst for signal enhancement. Hydrocortisone has been immobilized as a chiral selector on GR to discriminate electrochemical signals of mandelic acid (MA) enantiomers. A two-step electrodeposition strategy was used to fabricate hydrocortisone-loaded overoxidized polypyrrole film (HC-OPPy) on graphene-modified glassy carbon electrode, which was successfully utilized as a working electrode for direct monitoring of MA enantiomers based on an inhibitory sensing mechanism. The stepwise modification of the surface was confirmed by cyclic voltammetry, impedance spectroscopy, and scanning electron microscopy. Because of the different interactions of enantiomers with the chiral electroactive platform, voltammetric signals with different intensities were observed for S-MA and R-MA at 1.36 and 1.40 V (vs. Ag/AgCl), respectively. The introduced design for the chiral sensor, with exploiting the chemometrics tools such as partial least squares, principle component regression, and genetic algorithm, was able to discriminate highly overlapping signals of MA enantiomers in their mixtures. The hydrocortisone-based sensor showed a linear response towards MA enantiomers within a concentration range of 1.0–25 mM with a detection limit of 0.25 mM (S/N = 3). The sensor not only extends the enantioselective sensing of MA enantiomers but also stimulates new opportunities for investigating stereo-selective behavior of hydrocortisone. The recognition mechanism was also investigated using docking analysis and DFT calculations.

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Fabrication of graphene/Fe3O4@polythiophene nanocomposite and its application in the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples

Polythiophene (PT) was used as a surface modifier of graphene/Fe₃O₄ (G/Fe₃O₄) composite to increase merit of it, and also overcome some limitations and disadvantages of using G/Fe₃O₄ alone as solid phase extraction (SPE) sorbent. An in-situ chemical polymerization method was employed to prepare G/Fe₃O₄@PT nanocomposites. Application of this newly designed material in the magnetic SPE (MSPE) of polycyclic aromatic hydrocarbons (PAHs), as model analytes, in the environmental water samples was investigated. The characterization of the hybrid material was performed using transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform-infrared (FT-IR) spectroscopy and vibrating sample magnetometry. Seven important parameters, affecting the extraction efficiency of PAHs, including: amount of adsorbent, adsorption and desorption times, type and volume of the eluent solvent, initial sample volume and salt content of the sample were evaluated. The optimum extraction conditions were obtained as: 4 min for extraction time, 20 mg for sorbent amount, 100 mL for initial sample volume, toluene as desorption solvent, 0.6 mL for desorption solvent volume, 6 min for desorption time and 30% (w/v) for NaCl concentration. Good performance data were obtained at the optimized conditions. Detection limits were in the range of 0.009–0.020 μg L⁻¹ in the real matrix. The calibration curves were linear over the concentration ranges from 0.03 to 80 μg L⁻¹ with correlation coefficients (R²) between 0.995 and 0.998 for all the analytes. Relative standard deviations were ranged from 4.3 to 6.3%. Appropriate recovery values, in the range of 83–107%, were also obtained for the real sample analysis.     

Analysis of mono-nitrotoluenes in water samples by using nano-structured polypyrrol as a sorbent of solid-phase microextraction

Nano-structured polypyrrole (PPY) was used as a coating of solid-phase microextraction (SPME) fibre to increase the extraction efficiency of headspace solid phase microextraction (HS-SPME) of mono-nitrotoluene (MNT) isomers in water samples. The nano-structured PPY was prepared electrochemically by template-free method in the presence of dodecylbenzene sulphonate (DBS) as dopant. Nano-fibrous structures of PPY with a diameter in the range of 38–129 nm were obtained. The porous surface structure of the film, revealed by scanning electron microscopy (SEM), provided high surface areas and allowed for high extraction efficiency of MNT isomers. The extraction procedure was optimised by selecting the appropriate extraction parameters including the time and temperature of adsorption, salt concentration and stirring rate. The calibration graphs obtained by HS-SPME using the proposed fibre followed by GC-FID analysis were linear in a concentration range of 0.1–500 µg L^?1 (r > 0.999) with detection limits below 0.012 µg L^?1 for three isomers. Repeatability of the method was less than 6% (RSD%, n = 4). Good recoveries (88–108%) were obtained for the extraction of mono-nitrotoluenes in real water samples.     

Fibers coated with a graphene-polyaniline nanocomposite for the headspace solid-phase microextraction of organochlorine pesticides from seawater samples

We have prepared a fiber for solid-phase microextraction of organochlorine pesticides. A graphene-polyaniline composite was electrochemically deposited on a platinum fiber by exploiting the unique properties of polyaniline and graphene. The modified fiber displays thermal stability up to 320 °C and can be used more than 70 times. It possesses high extraction efficiency due to the high specific surface of graphene. The Pt fiber was used for the extraction and subsequent GC determination of the pesticides heptachlor, aldrin, endrin and p,p’-DDT in aqueous samples. The effects of extraction time, extraction temperature, stirring rate, salinity and headspace volume were optimized. Calibration plots are linear (with an R² of 0.990) in the 0.2 to 250 μg L^–1 concentration range, and the limits of detection are below 11 ng L^–1 (at an S/N of 3). The relative standard deviations for three replicate measurements with a single fiber were <11.0 %. The recovery of the pesticides from spiked seawater samples ranged from 81 % to 112 %.