Dispersive micro solid-phase extraction (DµSPE) with graphene oxide as adsorbent for sensitive elemental analysis of aqueous samples by laser induced breakdown spectroscopy (LIBS)

Introduction of a new and safe synthesis procedure for Ni-MOF-I in aqueous solution and its application for the extraction of some pesticides from different beverages

For the first time, this research introduces an analytical application of Ni-MOF-I, which was used as an adsorbent in a dispersive micro solid phase extraction procedure followed by dispersive liquid-liquid microextraction for the extraction and preconcentration of seven pesticides from different fruit juices. Also, Ni-MOF-I was synthesized by a new and green method with many advantages over the previously published synthesis procedures. For example, effortless and green synthesis, no need for autoclaves and ovens, and elimination of organic solvent usage are the main highlights. The synthesized Ni-MOF-I was characterized by applying nitrogen adsorption/desorption, energy-dispersive X-ray, scanning electron microscopy, Fourier transform infrared spectrophotometry, and X-ray diffraction analyses. The studied pesticides were extracted and preconcentrated by the proposed method. Then, the extracted analytes in the sedimented organic phase were injected into a gas chromatography-flame ionization detector. Acceptable analytical results such as low limits of detection (0.15-0.60 μg L-1) and quantification (0.50-2.0 μg L-1), reasonable extraction recoveries (51-80%), high enrichment factors (255-400), satisfactory relative standard deviation values of 4.8-7.2% (intra-day precision, n = 6) and 5.3-7.5% (inter-day precision, n = 4), and wide linear ranges were obtained. The proposed method can be introduced as an effective analytical technique based on Ni-MOF-I for the analysis of different pesticides in fruit beverages.

Properties and Characterization Techniques of Graphene Modified Asphalt Binders

Graphene is a carbon-based nanomaterial used in various industries to improve the performance of hundreds of materials. For instance, graphene-like materials have been employed as asphalt binder modifying agents in pavement engineering. In the literature, it has been reported that (in comparison to an unmodified binder) the Graphene Modified Asphalt Binders (GMABs) exhibit an enhanced performance grade, a lower thermal susceptibility, a higher fatigue life, and a decreased accumulation of permanent deformations. Nonetheless, although GMABs stand out significantly from traditional alternatives, there is still no consensus on their behavior regarding chemical, rheological, microstructural, morphological, thermogravimetric, and surface topography properties. Therefore, this research conducted a literature review on the properties and advanced characterization techniques of GMABs. Thus, the laboratory protocols covered by this manuscript are atomic force microscopy, differential scanning calorimetry, dynamic shear rheometer, elemental analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Consequently, the main contribution of this investigation to the state-of-the-art is the identification of the prominent trends and gaps in the current state of knowledge.

Detection of heavy metal ions using laser-induced breakdown spectroscopy combined with filter paper modified with PtAg bimetallic nanoparticles

The rapid and sensitive detection of heavy metal ions is important for environment and human health. Hence, the rapid and sensitive detection of multiple heavy metals simultaneously has become a critical issue. Here, we propose a method based on laser-induced breakdown spectroscopy (LIBS) combined with filter paper modified with PtAg bimetallic nanoparticles (BNPs) (LIBS-FP-PtAgBNPs) for the ultrasensitive detection of Hg²⁺, Cr³⁺, and Pb²⁺. The PtAgBNPs-modified filter paper was used to efficiently and specifically adsorb Hg, Cr, and Pb, and LIBS was used to detect the Hg, Cr, and Pb simultaneously. The limits of detection for Hg, Cr, and Pb were 0.5 μg/L (2.5 nM), 8 μg/L (0.15 μM), and 2 μg/L (9 nM), respectively. Furthermore, this method was successfully applied to determine the concentrations of Hg, Cr, and Pb in real spiked water samples. Compared with other methods based on nanoparticle sensing, LIBS-FP-PtAgBNPs is simpler to use and can achieve highly efficient enrichment, rapid separation, and sensitive detection of heavy metal ions. The optimal detections of Hg, Cr, and Pb were achieved in the pH range of 1-6. The developed method provides a new avenue to realize the rapid and sensitive detection of trace heavy metals in the environment.

Bifunctional Amine- and Thiol-Modified Ti3C2Tx MXene for Trace Detection of Heavy Metals

Surface functionalization of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, also known as MXenes, is a powerful approach for modification of their physical and chemical properties for new applications. In this study, we demonstrate the synthesis of a bifunctional Ti₃C₂T_x MXene modified with amine and thiol groups through a facile condensation reaction. We successfully employed the resulting NH₂/SH-Ti₃C₂T_x MXene as a solid phase in the ultrasonic-assisted dispersive micro solid-phase extraction (d-μ-SPE) method for the analytical determination of heavy metals at trace levels in food and soil samples. The prepared NH₂/SH-Ti₃C₂T_x MXene showed remarkable performance in the ultrasonic-assisted d-μ-SPE method with limits of detection of 0.12 and 2.30 ng mL^-1, with linear dynamic ranges of 0.50-90 μg L^-1 and 10-120 μg L^-1 for cadmium (Cd²⁺) and lead (Pb²⁺) ions, respectively. Furthermore, the extraction efficiencies were greater than 97%, with a relative standard deviation of less than 3% for five separate batch experiments in the determination of 5.0 μg L^-1 of Cd²⁺ and Pb²⁺. This study shows that NH₂/SH-Ti₃C₂T_x can be used as a simple, rapid, reliable, selective, and sensitive material in the d-μ-SPE method for the trace determination of Cd²⁺ and Pb²⁺ in soil and agricultural products. This study demonstrates the utility of MXenes for analytical chemistry and suggests that further advances in methods for the functionalization of MXenes can open new applications for these already exciting materials.

Determining metal elements in liquid samples using laser-induced breakdown spectroscopy and phase conversion technology

A phase conversion technology, involving the loading of brine samples with anionic polyacrylamide (APAM) colloidal droplets, is proposed to detect metal elements rapidly and accurately in liquid samples using laser-induced breakdown spectroscopy. The experimental conditions were optimized by comparing the obtained emission intensities and the signal-to-noise ratios, including the concentration of APAM, volume ratio of APAM solution to sample, delay time, and lens-to-sample distance (LTSD). Three kinds of complex brine samples with slightly soluble salts were used to test the analytical performance of the proposed method. The results show that the discrepancies of the concentrations of Li, Sr and Ca were 0.74-3.59%, compared with those obtained using inductively coupled plasma-optical emission spectrometry. This suggests that the proposed method can successfully determine metal elements in liquid samples, featuring short sample preparation time (less than 20 min), small sample volume (10 μL), and simple operation (no adsorption).

Ultrasensitive and Simultaneous Detection of Multielements in Aqueous Samples Based on Biomimetic Array Combined with Laser-Induced Breakdown Spectroscopy

Ultrasensitive detection of metallic elements in liquids has attracted considerable attention in fields such as environmental pollution monitoring and drinking water quality control. Hence, it is of great significance to develop a sensitive and simultaneous detection strategy for multiple metal elements in liquid. Laser-induced breakdown spectroscopy (LIBS) technology shows unique advantages because of its simple, rapid, and real-time in situ detection, but the laser energy will be greatly attenuated in the liquids; thus, the sensitivity of LIBS for direct detection of metal elements in liquid samples will decrease sharply. In this study, inspired by the structure of Stenocara beetle's back, a superhydrophobic biomimetic interface with hydrophilic array was prepared for enriching low-concentration targets into detection regions, and the biomimetic array LIBS (BA-LIBS) was successfully established. The ultrasensitive and simultaneous detection of nine metal elements in drinking water was realized based on the effective enrichment method. The limits of detection of the nine metal elements in mixed solution ranged from 8.3 ppt to 13.49 ppb. With these excellent properties, this facile and ultrasensitive BA-LIBS strategy might provide a new idea for the prevention and control of metal hazards in the liquid environment.

Triazine-triphenylphosphine based porous organic polymer as sorbent for solid phase extraction of nitroimidazoles from honey and water

A triazine-based porous organic polymer was prepared by facile solvothermal polymerization with cyanuric chloride and triphenyl phosphine as functional monomers. The polymer was characterized and then used for the first time as the sorbent for the effective solid-phase extraction of some nitroimidazoles (NDZs) (metronidazole, ronidazole, secnidazole, dimetridazole and ornidazole). The main experimental influencing parameters for the extraction including the eluent solvent, eluent volume, sample loading rate, sample solution pH, salt concentration and sample volume were investigated. The adsorption kinetics and adsorption isotherms were investigated to elucidate the possible adsorption mechanism. With the triazine-based porous organic polymer as the SPE adsorbent, trace NDZs were effectively extracted. The good enrichment capability for the NDZs was mainly attributed to the hydrogen binding interactions by the aromatic 1,3,5-trizine rings. After the SPE, the extracted analytes were analyzed by high-performance liquid chromatograph with ultraviolet detection. Under the selected conditions, the method had a good linear response for the analytes in the range of 0.06-120 ng mL^-1 for water and 1.5-1200 ng g^-1 for honey samples. The limits of detections (S/N=3) fell in the range of 0.02-0.06 ng mL^-1 for water and 0.5-1.5 ng g^-1 for honey samples. The method recoveries for the analytes for spiked samples were in the range of 80.3-118%. The method can be applied for the determination of the NDZs from real samples.

Evaluation of Thin Film Microextraction for trace elemental analysis of liquid samples using LIBS detection

An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene oxide was used as adsorbent material. The mould deposition procedure was found to produce more homogeneous graphene oxide layers, leading to more uniform distribution of the adsorbed analytes on the graphene oxide surface. Experimental parameters affecting the TFME procedure, such as the adsorbent amount and extraction time, were studied. Under optimum microextraction conditions, the analytical figures of merit of the proposed TFME-LIBS method were evaluated, leading to limits of detection ranging from 41 μg kg^-1 and 52 μg kg^-1. Method trueness, evaluated from the analysis of a real sample of bottle water, led to recovery values about 70%, indicating the existence of strong matrix effects probably due to the presence of major cations in the bottle water. After 50% dilution of the sample with deionized water, recoveries values improved to 100%-108%.

A Simple and Sensitive Dispersive Micro-Solid-Phase Extraction Coupled with High-Performance Liquid Chromatography for Quantification of Honokiol and Magnolol in Complex Matrices

Background

Honokiol and magnolol were considered as markers for the analysis of Cortex Magnoliae Officinalis, its related Chinese Patent Medicines and their metabolites. However, the determination of these two analytes in a water-soluble sample is difficult and therefore requires a more efficient method.

Objective

To develop a sensitive method for the determination of honokiol and magnolol in a water-soluble sample for better quality control of Cortex Magnoliae Officinalis and its related Chinese Patent Medicines.

Method

In this work, a combination of dispersive micro-solid-phase extraction (DMSPE) and high-performance liquid chromatography (HPLC) has been developed for simultaneous preconcentration and determination of honokiol and magnolol in complex bio-samples. Several experimental factors affecting the extraction efficiency were optimized by single factor test.

Results

Under the optimized extraction conditions, the proposed method exhibited good linearity of not less than 0.9998, satisfactory precision with relative standard deviation of less than 1.3%, and acceptable mean recoveries of 97.3% and 101.5% for honokiol and magnolol, respectively. Furthermore, the method exhibits extremely high sensitivity with detection limits of 0.0097 and 0.0231 ng/mL, which is even more sensitive than those methods developed by MS.

Conclusions

The method established in this study is fast, economic, accurate, easy to operate, and importantly well suited to the extraction and analysis of honokiol and magnolol in a real complex sample matrix.

Eco-friendly alginate encapsulated magnetic graphene oxide beads for solid phase microextraction of endocrine disrupting compounds from water samples

In the proposed method iron crosslinked alginate encapsulated magnetic graphene oxide beads were synthesized and used as an adsorbent for the microextraction of endocrine disrupting compounds from water samples and further analyzed by high performance liquid chromatography with ultraviolet detector. The beads were characterized using spectroscopic techniques, such as Fourier transform infra-red spectroscopy for the determination of different functional groups, Scanning electron microscopy for surface morphology, X-ray diffraction for phase determination and energy dispersive X ray spectroscopy for elemental composition. The results revealed that beads surface have functional groups of alginate and graphene oxide which are involved in π-π, n-πinteractions and hydrogen bonding for the bisphenol A and epichlorohydrin adsorption. The experimental conditions were studied for two endocrine disrupting compounds (Epichlorohydrin ad Bisphenol A) and at optimum conditions the adsorption capacity was 6.73 mgg^-1 for epichlorohydrin and 7.01 mgg^-1 for bisphenol A. The kinetic and equilibrium studies revealed that the adsorption process follow pseudo-second order kinetics and Langmuir equilibrium models. Analytical parameters were calculated for the microextraction of epichlorohydrin and bisphenol A. Limit of detection was 8.25 ngL^-1 and 13.99 ngL^-1 (n = 4) for epichlorohydrin and bisphenol A, respectively. Different solvents used for microextraction and maximum extraction of both endocrine disrupting compounds were obtained with methanol. The proposed method was applied to spiked samples and the recovery values were 97.17 ± 3.13% for epichlorohydrin and 99.46 ± 1.39% for bisphenol A. The magnetic graphene oxide encapsulated inside an alginate shows nontoxic green chemical with high extraction performance for toxic organic compounds in water treatment.

Magnetic Graphene Oxide Composite for the Microextraction and Determination of Benzophenones in Water Samples

Magnetite nanoparticles (Fe₃O₄) functionalized with graphene oxide (GO) have been synthesized through a silanization process of the magnetic nanoparticles with tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane and further coupling of GO. The synthesized nanomaterials have been characterized by several techniques, such as transmission electron microscopy (TEM), and infrared and Raman spectroscopy, which enabled the evaluation of the different steps of the functionalization process. The hybrid nanomaterial has been employed for the extraction of five benzophenones (benzophenone-1, benzophenone-3, 4-hydroxybenzophenone, benzophenone-6 and benzophenone-8) in aqueous samples by dispersive micro-solid phase extraction, combining the magnetic properties of magnetite nanoparticles with the excellent sorption capacity of graphene oxide via hydrophobic interactions with the analytes. The subsequent separation and quantification of the analytes was performed by liquid chromatography with tandem mass spectrometric detection, achieving limits of detection (LODs) in the range 2.5 to 8.2 μg·L^-1, with relative standard deviations ranging from 1.3-9.8% and relative recovering in the range 86 to 105%. Positive swimming pool water samples analysed following the developed method revealed the presence of benzophenones in from 14.3 to 39 μg·L^-1.

Matte photographic paper as a low-cost material for metal ion retention and elemental measurements with laser-induced breakdown spectroscopy

Matte photographic paper was explored as a low-cost material for metal-ion retention. The extraction was promoted by ultrasound, the mechanical waves of which forced adhesion to the photographic paper surface of an ion pair formed by DTAB (dodecyltrimethylammonium bromide) with the anionic coordination complex formed by metal ions and SPADNS (1,8-dihydroxy-2-(4-sulfophenylazo)naphthalene-3,6-disulfonic acid trisodium salt). As a proof of concept, the migration of copper ions present in aqueous solution to the solid phase and their direct measurement by laser-induced breakdown spectroscopy (LIBS) was evaluated. The main parameters that affected the extraction (paper type and sonication time) and analyte detection in the solid phase (delay, spot size and accumulated number of pulses) were optimised in a univariate way. The conditions influencing the complexation reaction and formation of the ion pair in aqueous solution (pH and copper, SPADNS and DTAB concentrations) were set according to a previous study. Under the optimised conditions, it was possible to use this extraction technology as an alternative in determining copper content in aqueous solutions by LIBS, overcoming the intrinsic difficulties of this instrumental technique in the analysis of liquid samples. The calibration curves were obtained in a linear range of 0.50-7.50 mg L^-1 copper in solution, with detection and quantification limits estimated at 0.08 and 0.24 mg L^-1, respectively. The precision of the method was less than 4.3% and the accuracy was checked by spike and recovery tests on liquid samples with different chemical compositions and by comparison of LIBS results with graphite furnace atomic absorption spectrometry data. The potential of the proposed method for extraction of Al³⁺, Ag⁺, Fe³⁺, Mn²⁺, Ni²⁺ and Zn²⁺ was also evaluated and adequate extraction efficiencies were obtained. The proposed method stands out due to its low cost and ease of execution.

Determination of 2,4-Dichlorophenoxyacetic acid in food and water samples using a modified graphene oxide sorbent and high-performance liquid chromatography

In the present work, dispersive micro-solid phase extraction (D-μ-SPE) method using magnetic graphene oxide tert-butylamine (GO/Fe₃O₄/TBA) nanocomposite, as an efficient sorbent, was applied for determining 2,4-dichlorophenoxyacetic acid (2,4-D) in water and food samples. Detection was carried out using high-performance liquid chromatography (HPLC) instrument. Influential parameters of D-μ-SPE such as sorbent and its amount, elution solvent and its volume, adsorption and desorption times and pH of sample solution were investigated and optimized. Under the optimized conditions, limit of detection and quantitation values were 0.007 and 0.02 μg/mL, respectively. Recovery data for several real samples were obtained within the range of 88.0-94.0% with a relative standard deviation (RSD) less than 7.5%. The proposed method was successfully applied to quantitative determination of 2,4-D in several vegetables and water samples.

Direct analysis of calcium in liquid infant formula via laser-induced breakdown spectroscopy (LIBS)

The present work illustrates the potential of laser-induced breakdown spectroscopy (LIBS) for the direct analysis of liquid food products. The aim of the experiment was to predict calcium content in ready-to-feed infant formula. The analysis was performed by a LIBS system coupled to a liquid sample chamber with a rotatory wheel that presents the liquid to the laser beam as a thin film. Multivariate analysis with partial least squares regression (PLSR) was performed to correlate LIBS spectral data to reference calcium contents. The obtained PLSR model exhibited a good fit and linearity, as indicated by the coefficients of determination for calibration (R_c²) and cross-validation (R_cv²), with values of 0.96 and 0.89, respectively. The robustness of the calibration model was assessed by external validation showing a root-mean-square error of prediction of 6.45 mg 100 mL^-1. These results demonstrated the potential of LIBS for real-time analysis of liquid food products.