Synthesis of Modified Magnetic Graphene Oxide with Mesoporous Silica for Extraction of the Pharmaceutical Compound Quercetin.

In this study, magnetic mesoporous silica-Fe3O4-graphene oxide nanoparticles (Fe3O4@GO@mSiO2) were synthesized and used as sorbents for magnetic solid-phase extraction (MSPE) of trace amounts of quercetin in natural samples (spinach, green pepper, dill, and red onion). The sorbent produced was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS). The effects of various experimental factors on the percent recovery of quercetin, including extraction time, desorption time, sample solution pH, and adsorbent amount were investigated. The Fe3O4@GO@mSiO2 strategy showed excellent stability and sensitivity for the determination of quercetin, with a suitable linear range of 20-800 µg L-1 and a detection limit of 5.2 µg L-1. The data indicate that Fe3O4@GO@mSiO2 has a specific surface area and suitable adsorption capacity for the determination of quercetin.

Simple and selective extraction of quercetin with microextraction in packed syringe method using modified glass powder by a molecularly imprinted polymer followed by spectrophotometric determination.

A new sample preparation method based on microextraction in packed syringe was developed for preconcentration of quercetin prior to its spectrophotometric determination. Molecularly imprinted polymers as packing material was used for higher extraction efficiency. First, glass powder as support material because of low cost and available substrate was modified, and then molecularly imprinted polymers were synthesized by the sol-gel method using 3-aminopropyltriethoxysilane as a functional monomer and tetraethyl orthosilicate as cross-linker agent. The combination of a molecularly imprinted polymers and microextraction in packed syringe increased the selectivity and sensitivity. The surface morphology and functionality of the prepared molecularly imprinted polymers was characterized using Fourier-transform infrared spectroscopy, Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and thermogravimetric analysis. Different influencing parameters on extraction efficiency such as effect of the number of sample sorption/desorption cycles, type and volume of desorption solvent, pH of the sample solution, and molecularly imprinted polymers amounts were optimized. Under the optimum condition, the proposed method displayed a linear range from 0.01 to 5 µg mL-1 and limit of detection 3.68 ng mL-1 . Relative standard deviation for three replicate determination of 1 µg mL-1 quercetin was 2.1 %. The proposed method was applied successfully for the selective extraction of quercetin from tea and coffee samples.

Preconcentration of Pb(II) by Magnetic Metal-Organic Frameworks and Analysis Using Graphite Furnace Atomic Absorption Spectroscopy.

In this study, a magnetic metal-organic framework (MOF) was synthesized based on magnetic Fe3O4, Cu(II), and benzene-1,3,5-tricarboxylic acid (Cu-BTC) as a sorbent for solid phase extraction (SPE) of trace amounts of Pb(II) in water and lettuce samples. Pb(II) ion was adsorbed on the magnetic MOF and easily separated by a magnet; therefore, no filtration or centrifugation was necessary. The analyte ions were eluted by HCl 0.5 mol·L-1 and analyzed via graphite furnace atomic absorption spectroscopy. The prepared sorbent was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Fourier transform-infrared (FT-IR) spectroscopy. Under optimal experimental conditions, the method had a linear range of 0.1-50 µg·L-1. The limits of detection and quantitation for lead were found to be 0.026 and 0.08 µg·L-1, respectively. The results showed that the prepared sorbent has high selectivity for Pb2+ even in the presence of other interfering metal ions.

Preparation of Molecular Imprinted Polymer Based on Chitosan as the Selective Sorbent for Solid-Phase Microextraction of Phenobarbital.

This study reports the construction of a novel SPME fiber based on chitosan and glutaraldehyde as coating material composites combined with high-performance liquid chromatography with an ultraviolet detector (HPLC-UV) for extraction and detection of phenobarbital. In this technique, the chitosan biopolymer, as a new coating of SPME fiber, was produced on the stainless-steel wire, using glutaraldehyde and phenobarbital as cross-linker and template, respectively. For comparison, a nonimprinted polymer was created using the same procedure to evaluate fiber selectivity (but without the addition of phenobarbital). The SPME-MIP fiber coating was characterized by field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis. The efficiency of fiber was then improved by adjusting the impact of numerous factors such as pH, extraction time, desorption time, desorption solvent, and stirring rate. The results showed that the proposed fiber has a linear range of 0.01-4 µg·mL-1, and detection limit of 7.5 ng·mL-1. The average recoveries in the four concentration levels for the spiked river and well water samples were 95.7 and 95.3%, with relative standard deviations of 3.8 and 5.9% for single fiber and between fibers, respectively.

Preparation of a New Solid-Phase Microextraction Fiber Based on Molecularly Imprinted Polymers for Monitoring of Phenobarbital in Urine Samples.

A simple solid-phase microextraction technique using molecularly imprinted polymers (MIP-SPME) was prepared to monitor phenobarbital in urine samples. In this technique, the fiber was prepared via insertion of the modified stainless-steel wire in the reaction solution including 3-aminopropyltriethoxysilane and tetraethyl orthosilicate in the presence of an acidic catalyst (acetic acid). The fabricated MIP-SPME fiber was utilized to selectively extract phenobarbital from urine samples and prepare it for detection through high-performance liquid chromatography with ultraviolet detection. The synthesized MIPs were characterized by several techniques such as Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, and thermal gravimetric analysis. The effects of various influencing factors on the extraction yield of phenobarbital were considered and optimized. The conditions that yielded the maximum extraction efficiency were as follows: pH of 5, 25 min extraction time, 500 rpm stirring rate, 15 min desorption time and using methanol as elution solvent. Within the range of concentrations of 0.02 to 100 µg mL-1, the method had linear characteristics, with a suitable coefficient of determination (0.9983). We determined limits of detection and limits of quantification to be 9.88 and 32.9 ng mL-1, respectively. The repeatability and reproducibility of the prepared fibers were 4.6 and 6.5%, respectively.

Indirect determination of mercury(II) by using magnetic nanoparticles, CdS quantum dots and mercury(II)-binding aptamers, and quantitation of released CdS by graphite furnace AAS.

This work describes an aptamer based method for highly sensitive determination of Hg(II). A Hg(II)-binding ssDNA aptamer was linked to silica-coated magnetic nanoparticles (magNPs). Then, a conjugate composed of graphene and CdS quantum dots (Gr-CdS) was linked to the complementary ssDNA. On mixing the two components, a duplex of type magNP-dsNNA-Gr/CdS is generated. If Hg(II) is added, it wills capturing the aptamer, and this leads to the release of Gr/CdS because of the formation of a stable thymine-Hg2+-thymine link. External magnetic force is used to remove the remaining complex. The released graphene-CdS is decomposed by HNO3 and injected into a graphite furnace AAS. The detectable amount of Cd is proportional to the concentration of Hg(II) in the sample. Under the optimal conditions, the method has a linear response in the 2.50 aM to 0.25 nM Hg(II) concentration range, and the detection limit is as low as 7.6 aM (at S/N = 3). It has high selectivity for Hg(II) over other metal ions. Graphical abstract.

Electrochemical exfoliation of pencil graphite for preparation of graphene coating as a new versatile SPME fiber for determination of polycyclic aromatic hydrocarbons by gas chromatography.

A graphene coating was prepared through electrochemical exfoliation of pencil graphite and then used as a fiber coating for headspace solid-phase microextraction of polycyclic aromatic hydrocarbons (PAHs) from water samples by GC analysis technique with flame ionization detector since flame ionization detector work according to the principle of ions released in the combustion of the sample species if there are any organic compounds. The graphene layers were produced by applying an anodic voltage of +2 V to the pencil graphite electrode in 1 M sulfuric acid solution as an electrolyte. The adsorbent was characterized by using scanning electron microscopy. Following thermal desorption, the PAHs (specfically naphthalene, acenaphthene, fullerene, phenanthrene, anthracene and fluoranthene) were quantified by GC. Under optimum conditions (extraction temperature, 65 °C; extraction time, 35 min; salt concentration of 20% w/v; desorption temperature, 260 °C; desorption time, 5 min), the limits of detection range between 10 and 90 ng L-1, and the linear ranges extend from 0.05-50 µg L-1. The repeatability of the extraction process and the fiber-to-fiber reproducibility were in the ranges of 4.3-0.2% and 7.3-9.8%, respectively. Graphical abstractSchematic representation of electrochemical exfoliation of pencil core to prepare a headspace solid phase microextraction (HS-SPME) graphene fiber coating. After applying a voltage, the graphene nanosheets thus produced are used for determination of polycyclic aromatic hydrocarbons (PAHs) in water samples.

Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry.

Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between -2.1 to 13.9 for lidocaine, -4.2 to 11.0 for prilocaine and between -4.5 to -2.4 for ropivacaine in plasma samples while the values were ranged from -4.6 to 1.6 for lidocaine, from -4.2 to 15.5 for prilocaine and from -3.3 to -2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L-1 for all of the studied drugs. The correlation coefficients values were ≥0.995. The limit of detection values were obtained 4 nmol L-1 for lidocaine and prilocaine, and 2 nmol L-1 for ropivacaine.

Electrochemical preparation of zinc oxide/polypyrrole nanocomposite coating for the highly effective solid-phase microextraction of phthalate esters.

In this work, zinc oxide/polypyrrole nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid-phase microextraction fiber coating for extraction of ultra-trace amounts of environmental pollutants, namely, phthalate esters, in water samples. The fiber nanocomposite were prepared by a two-step process including the electrochemical deposition of polypyrrole on the surface of stainless steel in the first step, and electrochemical deposition of zinc oxide nanosheets in the second step. Porous structure together with zinc oxide nanosheets with the average diameter of 30 nm were observed on the surface by using scanning electron microscopy. The effective parameters on extraction of phthalate esters (i.e., extraction temperature, extraction time, desorption temperature, desorption time, salt concentration, and stirring rate) were investigated and optimized by one-variable-at-a-time method. Under optimized conditions (extraction temperature, 90°C; extraction time, 40 min; desorption temperature, 270°C; desorption time, 5 min; salt concentration, 25% w/v; and stirring rate, 1000 rpm), the limits of detection were in the range of 0.05-0.8 µg/L, and the repeatability and fiber-to-fiber reproducibility were in the ranges of 6.1-7.3% and 8.7-10.2%, respectively.

Evaluation of Graphene as a Solid-Phase Extraction Sorbent for the Preconcentration and Determination of Trace Amounts of Nickel in Food Samples Prior to Flame Atomic Absorption Spectrometry.

A sensitive and low cost SPE method for the extraction, preconcentration, and flame atomic absorption spectrometric determination of nickel at ng/mL levels is described. Parameters governing the extraction efficiency including pH of the solution, eluent type, sample volume, and matrix ions were investigated for optimization of the presented procedure. The enhancement factor was calculated as 96.5. The calibration curve was linear with R2 of 0.999 in the concentration range from 2 to 200 ng/mL. The RSD was 5.35% (n=7), the LOD was 0.588 ng/mL, and relative recoveries from vegetable samples ranged between 99 and 109.5%.