Enhancing Analytical Potential for Ultratrace Analysis of Inorganic Oxyanions Using Extraction Procedures with Layered Double Hydroxides

This article provides an overview of the use of layered double hydroxides (LDHs) as effective sorbents in various extraction methods, including column-based solid-phase extraction (SPE), dispersive solid-phase extraction (DSPE), and magnetic solid-phase extraction (MSPE), for the separation and preconcentration of inorganic oxyanions of chromium, arsenic, and selenium. The primary focus is on enhancing the analytical performance of spectrometric detection techniques, particularly in terms of sensitivity and selectivity when analyzing low concentrations of target analytes in complex matrices. LDHs, which can be readily prepared and structurally modified with various substances, offer promising potential for the development of novel analytical methods. When used in analytical extraction procedures and following careful optimization of experimental conditions, the developed methods have yielded satisfactory results, as documented by studies reviewed in this paper. This review is intended to assist analytical chemists in scientific laboratories involved in developing new extraction procedures.

Chemometrically-aided general approach to novel adsorbents studies: Case study on the adsorption of pharmaceuticals by the carbonized Ailanthus altissima leaves

A chemometrically based approach was applied to select the most efficient drug adsorbent among the biochars obtained from the novel feedstock, the leaves of the invasive plant (Ailanthus altissima). The representative target adsorbates (atenolol, paracetamol, ketorolac and tetracycline) were selected on the basis of their physicochemical properties to cover a wide chemical space, which is the usual analytical challenge. Their adsorption was investigated using design of experiments as a comprehensive approach to optimise the performance of the adsorption system, rationalise the procedure and overcome common drawbacks. Among the response surface designs, the central composite design was selected as it allows the identification of important experimental factors (solid-to-liquid ratio, pH, ionic strength) and their interactions, and allows the selection of optimal experimental conditions to maximise adsorption performance. The biochars were prepared by pyrolysis at 500 °C and 800 °C (BC-500 and BC-800) and the ZnCl2-activated biochars were prepared at 650 °C and 800 °C (AcBC-650 and AcBC-800). The FTIR spectra revealed that increasing the pyrolysis temperature without activator decreases the intensity of all bands, while activation preserves functional groups, as evidenced by the spectra of AcBC-650 and AcBC-800. High temperatures during activation promoted the development of an efficient surface area, with the maximum observed for AcBC-800 reaching 347 m2 g-1. AcBC-800 was found to be the most efficient adsorbent with removal efficiencies of 34.1, 51.3, 55.9 and 38.2 % for atenolol, paracetamol, ketorolac and tetracycline, respectively. The models describing the relationship between the removal efficiency of AcBC-800 and the experimental factors studied, showed satisfactory predictive ability (predicted R2 > 0.8) and no significant lack-of-fit was observed. The results obtained, including the mathematical models, the properties of the adsorbates and the adsorbents, clearly indicate that the adsorption mechanisms of activated biochars are mainly based on hydrophobic interactions, pore filling and hydrogen bonding.

Neodymium sorption on the Na-form of Transcarpathian clinoptilolite

The sorption properties of Na-modified Ukrainian Transcarpathian clinoptilolite towards neodymium aqueous solutions under dynamic conditions have been investigated. The sorption capacity of the Na-from of Transcarpathian clinoptilolite towards Nd(III) significantly depends on the concentration of neodymium salt, the pH of the solution, and the heat treatment temperature of the sorbent. Nd(III) is most efficiently sorbed from slightly alkaline solutions (pH 8.5), mainly by adsorption of neutral hydrolyzed forms of Nd(OH)3 on the surface of Na-clinoptilolite samples preheated at 75 °C. During the passage of an Nd(III) solution with a concentration of 1 μg mL-1 through the sorbent at a rate of 3 mL min-1 under optimal conditions, the sorption capacity of Na-clinoptilolite is 7.2 mg g-1, which is in 4 and 2.3 times higher than that of natural and acid-modified forms of this zeolite. It is shown that under the experimental conditions with an increase in the flow rate, the thickness of the stationary surface layer decreases, which leads to a decrease in the sorption capacity of Na-clinoptilolite. The best Nd(III) desorbents are solutions of mineral acids and acidified solutions of alkali metal salts (except NaCl), which provide 93-98 % extraction of lanthanide from the zeolite matrix. The method for neodymium trace amounts preconcentration from aqueous solutions in a solid-phase extraction mode with a further determination of this rare earth element by a spectrophotometric method was developed. The detection limit of this method is 0.75 ng mL-1 and the linearity was evaluated in the range of 2.5-500 ng mL-1.

Homogeneous liquid-liquid extraction as an alternative sample preparation technique for biomedical analysis

Liquid-liquid extraction is a widely used technique of sample preparation in biomedical analysis. In spite of the high pre-concentration capacities of liquid-liquid extraction, it suffers from a number of limitations including time and effort consumption, large organic solvent utilization, and poor performance in highly polar analytes. Homogeneous liquid-liquid extraction is an alternative sample preparation technique that overcomes some drawbacks of conventional liquid-liquid extraction, and allows employing greener organic solvents in sample treatment. In homogeneous liquid-liquid extraction, a homogeneous phase is formed between the aqueous sample and the water-miscible extractant, followed by chemically or physically induced phase separation. To form the homogeneous phase, aqueous samples are mixed with water-miscible organic solvents, water-immiscible solvents/cosolvents, surfactants, or smart polymers. Then, phase separation is induced chemically (adding salt, sugar, or buffer) or physically (changing temperature or pH). This mode is rapid, sustainable, and cost-effective in comparison with other sample preparation techniques. Moreover, homogeneous liquid-liquid extraction is more suitable for the extraction of delicate macromolecules such as enzymes, hormones, and proteins and it is more compatible with liquid chromatography with tandem mass spectrometry, which is a vital technique in metabolomics and proteomics. In this review, the principle, types, applications, automation, and technical aspects of homogeneous liquid-liquid extraction are discussed.

Beech sawdust based adsorbents for solid-phase extraction of pesticides and pharmaceuticals

Carbonaceous solid-phase extraction (SPE) sorbent, efficient in isolation and enrichment of multiclass pesticides and pharmaceuticals from water, was synthesized starting from cheap waste beech sawdust and using KOH as the activated agent. The first step in carbon material preparation was hydrothermal carbonization of the waste beech sawdust. Following hydrothermal treatment, the obtained material was activated, using different amounts of KOH. It was found that applied activation leads to changes in material structure, an increase in specific surface area, and a decrease in the number of surface oxygen groups compared to carbonized sample. SPE procedure of multiclass pesticides and pharmaceuticals from water using activated carbonized beech sawdust (AcSD) was optimized by selecting the appropriate elution solvents, the sample pH, and the sample volume to obtain the highest enrichment efficiency. The optimized SPE procedure was applied for water analysis using different AcSD samples as a sorbent for analyte preconcentration. Activated carbon sorbent, obtained with the highest amount of KOH, showed the highest recoveries regarding the most analytes, which were comparable with the recoveries obtained by commercial cartridges.

Solid phase extraction of β-sitosterol and α-tocopherol from sunflower oil deodorizer distillate using desilicated zeolite

In this study, the efficiency of using zeolite-based adsorbents in a solid phase extraction (SPE) procedure of α-tocopherol and β-sitosterol isolation from Sunflower Oil Deodorizer Distillate (SuDOD) with­out pre-treatment was investigated. The results showed that 99.2% α-tocopherol and 97.3% β-sitosterol were suc­cessfully isolated as pure fractions from SuDOD, when desilicated ZSM-5-type zeolite (DSiZSM-5) was used as adsorbent on a SPE. A simple and rapid HPLC method for simultaneous α-tocopherol and β-sitosterol analysis was developed and validated according to AOAC guidelines. It was found that the inclusion of a DSiZSM-5 SPE step increased the precision of the α-tocopherol and β-sitosterol analysis. In conclusion, DSiZSM-5 zeo­lite was proven to be an efficient adsorbent which can be used not only for the recovery of α-tocopherol and β-sitosterol from SuDOD in industrial scale, but also in a laboratory scale clean-up method prior to the analysis of α-tocopherol and β-sitosterol.

Electrochemically synthesized NiFe layered double hydroxide modified Cu(OH)2 needle-shaped nanoarrays: A novel sorbent for thin-film solid phase microextraction of antifungal drugs

Herein, we applied a simple electrosynthesis process to deposit nickel-iron layered double hydroxides (NiFe LDH) on the surface of copper hydroxide (Cu(OH)₂) needle-shaped nanoarrays and introduce a new sorbent for thin-film solid phase microextraction (TF-SPME). For this purpose, the nanoarrays were grown via electrochemical anodization on a copper foil's surface and then modified with NiFe LDH. The synthesized sorbent was characterized by field emission-scanning electron microscopy, Brunauer-Emmett-Teller (BET), and Barrett-Joiner-Halenda (BJH) analysis, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The Cu(OH)₂-NiFe LDH based TF-SPME method was used to measure antifungal drugs in veterinary plasma samples followed by HPLC-UV analysis. The effects of various parameters in the extraction efficiency, including pH (5.0), extraction time (20 min), stirring rate (500 rpm), and salt effect (5.0%), type of eluent (acetonitrile), eluent volume (100 μL) and desorption time (5 min) were thoroughly optimized. Under the optimum conditions, limits of detection for ketoconazole, clotrimazole, and miconazole were obtained below 10 ng mL^-1. Intra-day, inter-day and film-to-film RSDs% were obtained less than 6.2%, 7.3% and 7.0%, respectively. Moreover, calibration plots were linear from 30 to 5000 ng mL^-1 for ketoconazole, 8.0-1000 ng mL^-1 for clotrimazole, and 15-1000 ng mL^-1 for miconazole, with determination coefficients between 0.9937 and 0.9971. Finally, good relative recoveries (%) in the range of 85-97% were obtained for measuring trace amounts of antifungal drugs in dogs' plasma samples. As a result, the method can be considered as an appropriate alternative to the conventional sample preparation methods for measuring trace amounts of antifungal drugs in biological samples.

Ultrasound-assisted dispersive micro-solid-phase extraction based on N-doped mesoporous carbon and high-performance liquid chromatographic determination of 1-hydroxypyrene in urine samples

In this research, a new ultrasound-assisted dispersive micro-solid-phase extraction method based on N-doped mesoporous carbon sorbent followed by high-performance liquid chromatography equipped with diode array detector for trace measurement of 1-hydroxypyrene as a metabolite of exposure to polycyclic aromatic hydrocarbons was optimized. Herein, the hard template method was used for the preparation of N-doped mesoporous carbon sorbent. The prepared sorbent was characterized using the Brunauer-Emmett-Teller method, transmission electron microscopy, and elemental analysis. Parameters affecting the extraction of the target metabolite were investigated using the Box-Behnken design method. Considering optimum parameters, the plotted calibration curve for 1-hydroxypyrene was linearly correlated with the concentration span of 0.1-50 μg/L for urine media. The accuracy of the optimized procedure was examined through the relative recovery tests on the fortified urine specimens. The relative recoveries fell between 95 and 101%. The method detection limit of the proposed procedure was also calculated to be 0.03 μg/L.

3D Printing in analytical sample preparation

In the last 5 years, additive manufacturing (three-dimensional printing) has emerged as a highly valuable technology to advance the field of analytical sample preparation. Three-dimensional printing enabled the cost-effective and rapid fabrication of devices for sample preparation, especially in flow-based mode, opening new possibilities for the development of automated analytical methods. Recent advances involve membrane-based three-dimensional printed separation devices fabricated by print-pause-print and multi-material three-dimensional printing, or improved three-dimensional printed holders for solid-phase extraction containing sorbent bead packings, extraction disks, fibers, and magnetic particles. Other recent developments rely on the direct three-dimensional printing of extraction sorbents, the functionalization of commercial three-dimensional printable resins, or the coating of three-dimensional printed devices with functional micro/nanomaterials. In addition, improved devices for liquid-liquid extraction such as extraction chambers, or phase separators are opening new possibilities for analytical method development combined with high-performance liquid chromatography. The present review outlines the current state-of-the-art of three-dimensional printing in analytical sample preparation.

Metal-Organic Framework@Carbon Hybrid Magnetic Material as an Efficient Adsorbent for Pollutant Extraction

The preparation of a hybrid magnetic metal-organic framework (MOF)@carbon from a MOF-derived porous carbon is reported. MOF-74(Co) is used as a precursor for the synthesis of a magnetic carbon with homogeneous cobalt particle distribution (C-MOF-74) by a direct carbonization step. The cobalt particles present in the carbon are partially converted to zeolitic imidazolate framework (ZIF)-67 by reaction with 2-methylimidazole to obtain a core-shell ZIF-67@C-MOF-74. The effect of the reaction time and 2-methylimidazole concentration in the conversion procedure is studied by X-ray diffraction and scanning microscopy. Because of its high surface area, dual porosity, and magnetic properties, ZIF-67@C-MOF-74 exhibits high extraction capacity (180 mg g^-1), fast adsorption rate, and excellent recyclability for Congo red adsorption. In addition, the prepared material shows high efficiency in the extraction of different phenolic compounds. The developed procedure can be easily adapted to different carbons and MOFs, thus potentially enabling the preparation of a wide number of new hybrid materials.

Recent advances in the application of layered double hydroxides in analytical chemistry: A review

In recent years, layered double hydroxides (LDHs) have garnered a lot of attention in analytical chemistry, due to their advantages such as relatively simple synthesis, low cost, possession of large specific surface area and high catalytic activity, and biocompatibility. The most common applications of LDH in analytical chemistry such as sorbents in sample extraction, electrode materials in electrochemical sensing and color indicators in colorimetric detection have been well reported. Generally, the LDHs are prepared as composites with nanomaterials, or constructed with specific three-dimensional structures, befitting the applications desired for them. However, the applications of LDHs (as extraction sorbents, color indicators and in electrochemical sensing) are usually limited in these scenarios. To help address these challenges, future trends and developmental prospects of LDHs materials in analytical chemistry are discussed in this article. Besides, the strategies associated with the design of LDHs, including the structural aspects, for potential analytical applications are presented and reviewed.

Materials for Solid-Phase Extraction of Organic Compounds

This review provides an overview of the most recent developments involving materials for solid-phase extraction applied to determine organic contaminants. It mainly concerns polymer-based sorbents that include high-capacity, as well as selective sorbents, inorganic-based sorbents that include those prepared using sol-gel technology along with structured porous materials based on inorganic species, and carbon nanomaterials, such as graphene and carbon nanotubes. Different types of magnetic nanoparticles coated with these materials are also reviewed. Such materials, together with their main morphological and chemical features, are described, as are some representative examples of their application as solid-phase extraction materials to extract organic compounds from different types of samples, including environmental water, biological fluids, and food.

Cork sheet as a sorptive phase to extract hormones from water by rotating-disk sorptive extraction (RDSE)

This work reports for the first time the use of laminar cork as a sorptive phase in a microextraction technique, rotating-disk sorptive extraction (RDSE). Typical hormones (estrone, estradiol, estriol and ethinyl estradiol) were selected as analyte models and extracted from wastewater samples on laminar cork with statistically equivalent extraction efficiency to that provided by Oasis HLB. The cork characterization was performed by confocal fluorescence microscopy (CLSM), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), allowing the identification of lignin, suberin and polysaccharides (cellulose and hemicellulose) as the main components of the cork. The best conditions for extraction were as follows: rotation velocity of the disk, 2000 rpm; extraction time, 45 min; and sample volume, 20 mL. The analytical features of the developed method show that calibration curves for all analytes have R² values higher than 0.99. The absolute recoveries were higher than 63%, and the precision, expressed as relative standard deviation, ranged from 2 to 16%. The LOD and LOQ ranges were 3-19 and 10-62 ng L^-1, respectively. The proposed method was applied to the analysis of wastewater, and the concentrations of hormones in a wastewater treatment plant in Santiago, Chile, ranged from <LOQ to 48 ng L^-1.

Metal-Organic Frameworks for Food Safety

Food safety is a prevalent concern around the world. As such, detection, removal, and control of risks and hazardous substances present from harvest to consumption will always be necessary. Metal-organic frameworks (MOFs), a class of functional materials, possess unique physical and chemical properties, demonstrating promise in food safety applications. In this review, the synthesis and porosity of MOFs are first introduced by some representative examples that pertain to the field of food safety. Following that, the application of MOFs and MOF-based materials in food safety monitoring, food processing, covering preservation, sanitation, and packaging is overviewed. Future perspectives, as well as potential opportunities and challenges faced by MOFs in this field will also be discussed. This review aims to promote the development and progress of MOF chemistry and application research in the field of food safety, potentially leading to novel solutions.

Magnetic metal-organic frameworks-101 functionalized with graphite-like carbon nitride for the efficient enrichment of glucocorticoids in cosmetics

In this work, magnetic metal-organic frameworks-101 functionalized with graphite-like carbon nitride material (Fe₃O₄/g-C₃N₄/MIL-101) has been simply prepared for the efficient enrichment of glucocorticoids in cosmetics. Due to the introduction of g-C₃N₄, the water stability of MIL-101 has been greatly improved. This composite material also showed better selectivity for glucocorticoids than those for polycyclic aromatic hydrocarbons and benzene compounds due to the hydrogen bonding effect with g-C₃N₄ and the size-matching effect with MIL-101. When the prepared material was used as the sorbents in magnetic solid-phase extraction (MSPE) and coupled with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS), a sensitive MSPE-UPLC-MS/MS method was developed. Under the optimal conditions, the calibration curves were linear over the concentration ranging from 0.01 to 2 μg/L with correlation coefficients (R²) between 0.9915 and 0.9995. The limit of detection (LOD) was as low as 2 ng/L with the RSDs lower than 5.5%. The recoveries ranged from 77.3% to 113%. The LOD of glucocorticoids in real samples analysis was improved by nearly three orders of magnitude compared to current literature records. The results indicated that Fe₃O₄/g-C₃N₄/MIL-101 could be used as MSPE extractant to determine glucocorticoids in complex cosmetics matrix.

Selective extraction of aliphatic amines by functionalized mesoporous silica-coated solid phase microextraction Arrow

Mesoporous silica-coated solid phase microextraction (SPME) Arrow systems were developed for capturing of low-molecular-weight aliphatic amines (LMWAAs) from complicated sample matrices. Specifically, silicas of type MCM-41, SBA-15 and KIT-6 were chosen as substrates to afford size-exclusion selectivity. They possess ordered multidimensional pore-channel structures and mesopore sizes between 3.8 and 8.2 nm. Their surface acidity was enhanced by grafting them with a layer of titanium hydrogenphosphate (-TP). This enhanced the chemical selectivity for basic LMWAAs. The siliceous coatings increased the extraction of ethylamine, diethylamine (DEA) and triethylamine (TEA) by factors of 18.6–102.5, 4.8–10.8 and 2.6–4.0, respectively, when compared to the commercial SPME Arrow with polydimethylsiloxane/divinylbenzene coating. Among them, the MCM-41 and MCM-41-TP coated SPME Arrows demonstrated exceptional selectivity towards LMWAAs that were quantified by gas chromatography-mass spectrometry (GC-MS). The total peak area ratios of LMWAAs/ten competing compounds were 25.4 and 36.3, respectively. The extraction equilibrium was reached within 20–30 min. The MCM-41 and MCM-41-TP derived SPME Arrows gave very similar results (18.4 ± 2.1–376 ± 12 ng g⁻¹ to DEA and TEA) when applied to urban mushroom samples. SPME Arrow with MCM-41 coatings followed by GC-MS was applied also to the analysis of atmospheric air and urine samples resulting in high selectivity due to the size and mesoporous structure of the functionalized silica, and its chemical interactions with the LMWAAs.

Graphical abstract

Simple method for the determination of personal care product ingredients in lettuce by ultrasound-assisted extraction combined with solid-phase microextraction followed by GC-MS

A simple method for the simultaneous determination of personal care product ingredients: galaxolide, tonalide, oxybenzone, 4-methylbenzyliden camphor, padimate-o, 2-ethylhexyl methoxycinnamate, octocrylene, triclosan, and methyl triclosan in lettuce by ultrasound-assisted extraction combined with solid-phase microextraction followed by gas chromatography with mass spectrometry was developed. Lettuce was directly extracted by ultrasound-assisted extraction with methanol, this extract was combined with water, extracted by solid-phase microextraction in immersion mode, and analyzed by gas chromatography with mass spectrometry. Good linear relationships (25-250 ng/g, R2  > 0.9702) and low detection limits (1.0-25 ng/g) were obtained for analytes along with acceptable precision for almost all analytes (RSDs < 20%). The validated method was applied for the determination of personal care product ingredients in commercial lettuce and lettuces grown in soil and irrigated with the analytes, identifying the target analytes in leaves and roots of the latter. This procedure is a miniaturized and environmentally friendly proposal which can be a useful tool for quality analysis in lettuce.