Solid-phase Extraction Material Research Articles

Fabricating Ultrathin Imprinting Layer for Fast Capture of Valsartan via a Metal Affinity-Oriented Surface Imprinting Method.

Rapid separation and enrichment of targets in biological matrixes are of significant interest in multiple life sciences disciplines. Molecularly imprinted polymers (MIPs) have vital applications in extraction and sample cleanup owing to their excellent specificity and selectivity. However, the low mass transfer rate, caused by the heterogeneity of imprinted cavities in polymer networks and strong driving forces, significantly limits its application in high-throughput analysis. Herein, one novel metal affinity-oriented surface imprinting method was proposed to fabricate an MIP with an ultrathin imprinting layer. MIPs were prepared by immobilized template molecules on magnetic nanoparticles (NPs) with metal ions as bridges via coordination, and then polymerization was done. Under the optimized conditions, the thickness of the imprinting layer was merely 1 nm, and the adsorption toward VAL well matched the Langmuir model. Moreover, it took just 5 min to achieve adsorption equilibrium significantly faster than other reported MIPs toward VAL. Adsorption capacity still can reach 25.3 mg/g ascribed to the high imprinting efficiency of the method (the imprinting factor was as high as 5). All evidence proved that recognition sites were all external cavities and were evenly distributed on the surface of the NPs. The obtained MIP NPs exhibited excellent selectivity and specificity toward VAL, with good dispersibility and stability. Coupled with high-performance liquid chromatography, it was successfully used as a dispersed solid phase extraction material to determine VAL in serum. Average recoveries are over 90.0% with relative standard deviations less than 2.14% at three spiked levels (n = 3). All evidence testified that the MIPs fabricated with the proposed method showed a fast trans mass rate and a large rebinding capacity. The method can potentially use high-throughput separation and enrichment of target molecules in batch samples to meet practical applications.

Fabrication of Magnetic Molecularly Imprinted Polymers for Selective Extraction of Dibutyl Phthalates in Food Matrices.

In this study, a novel magnetic molecularly imprinted polymeric material (Fe3O4@MOF@MIP-160) with a metal-organic backbone (Fe3O4@MOF) carrier was prepared using dibutyl phthalate (DBP) as a template. The material can be used for the efficient, rapid, and selective extraction of trace amounts of phthalic acid esters (PAEs) in food and can detect them via gas chromatography-mass spectrometry (GC-MS). The synthesis conditions of the materials were optimized to prepare the Fe3O4@MOF@MIP160 with the highest adsorption performance. Transmission electron microscopy (TEM), Fourier Transform Infrared Spectra (FT-IR), Vibration Sample Magnetic (VSM), and the Brunauer-Emmett-Teller (BET) method were used to characterize the materials. Compared with Fe3O4@MOF and the magnetic non-imprinted polymeric material (Fe3O4@MOF@NIP), Fe3O4@MOF@MIP-160 possesses the advantages of easy and rapid manipulation of magnetic materials, the advantages of high specific surface area and the stability of metal-organic frameworks, and the advantages of high selectivity of molecularly imprinted polymers. Fe3O4@MOF@MIP-160 has good recognition and adsorption capacity for di-butyl phthalate (DBP) and diethylhexyl phthalate (DEHP): the adsorption capacity for DBP and DEHP is 260 mg·g-1 and 240.2 mg·g-1, and the adsorption rate is fast (reaching equilibrium in about 20 min). Additionally, Fe3O4@MOF@MIP160 could be recycled six times, making it cost-effective, easy to operate, and time-saving as compared to traditional solid-phase extraction materials. The phthalate ester content in drinking water, fruit juice, and white wine was analyzed, with recoveries ranging from 70.3% to 100.7%. This proved that Fe3O4@MOF@MIP160 was suitable for detecting and removing PAEs from food matrices.

Selective solid phase extraction of phototoxic furanocoumarins using molecularly imprinted polymers

Furanocoumarins are secondary plant metabolites found in citrus plants. Essential oils from these plants are widely used in cosmetic products. They have attracted attention for their phototoxicity, which can even lead to skin burns. Therefore, the furanocoumarin concentration is controlled by the European Union according to Regulation (EC) No. 1223/2009, where a limit of 1 mg kg−1 is specified in sun protection and bronzing agents. This study describes the synthesis of two molecularly imprinted polymers (methacrylamide and methacrylic acid as monomers) as novel materials for solid phase extraction. After optimisation of the extraction protocol, both polymers gave satisfying recovery results for a furanocoumarin standard mixture containing the six markers proposed by the International Fragrance Association (IFRA). Furthermore, spiked sun oil samples were extracted using an adapted extraction protocol. Since the studies showed promising results including 75–149 % recovery and 100 % loading efficiency for the methacrylic acid polymer, a validation of the analytical method was performed. Analysis was performed using HPLC-MS/MS in high specificity multi-reaction monitoring mode. The validation showed acceptable results for most parameters. In addition, a comparison with commercially available Strata-X cartridges was completed, revealing superior recovery performance of the molecularly imprinted polymer. In conclusion, molecularly imprinted polymers represent a novel and efficient method for selective solid-phase extraction of phototoxic furanocoumarins.

Application of solid-phase extraction materials from ion liquids for the analysis of carbamate pesticide

In this study, ionic liquid immobilised onto silica gel material SiO2-(CH2)3-N(Oct)3Br was successfully synthesised and characterised by Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). This material was applied as the stationary phase of solid-phase extraction for the enrichment of trace amounts of carbamate pesticides in water. The cartridge was eluted with 5 ml of acetonitrile (ACN), blow-dried with nitrogen gas, and re-dissolved in ACN:H2O (40:60, v/v) and analysed by high-performance liquid chromatography - ultraviolet (HPLC-UV) at 210 and 245 nm. Within this process, elution of the cartridge with 5 ml of acetonitrile (ACN) was followed by nitrogen gas blow-drying and subsequent re-dissolution in ACN:H2O (40:60, v/v), culminating in analysis by HPLC-UV at 210 and 245 nm. Optimisation of conditions facilitated the analysis of carbamate pesticides, with the limit of quantitation (LOQ)ranging from 0.36-2.00 μg/l for tap water and 0.4-3.5 μg/l for river water. Furthermore, the method exhibited favourable repeatability, with a relative standard deviation (RSD) of less than 10%, thereby meeting the Association of Official Analytical Collaboration (AOAC) standards.

Affordable cellulose-based solid phase extraction adsorbent for efficient chromatographic analysis of trace contaminants in environmental waters for developing countries

The current work reports on a new low-cost solid phase extraction (SPE) material obtained by crosslinking cellulose with 4,4–methylenebisphenyldiisocyanate (CMDI-1) for the pre-concentration of two contaminants of emerging concern (CEC): Chloramphenicol (CAP) and Bisphenol-A (BPA) from water. The results obtained show good analytical performance with low Limit of Detection of 71.9 ng/L and 10 ng/L for the pre-concentration of CAP and BPA respectively, and a good linear range between 0.5 and 8 µg/L, with r2 values > 0.99. The application of the developed method for the analysis of real water samples achieved good percentage recoveries (86.8 – 96.2 %), comparable to that of an expensive commercial HLB adsorbent (89.8 – 107 %). Response Surface Methodology modelling indicates that adsorbent dose, elution volume, and sample volume had a significant influence on CAP recovery, while solution pH, elution volume, and ionic strength had a significant influence on BPA recovery. From our economic assessment, a pack of 30 SPE tubes of 500 mg CMDI-1 SPE adsorbent will cost 82 % less than a similar amount of Oasis HLB adsorbent. This study demonstrates and validates a feasible and inexpensive approach to the use of cellulose to develop low-cost SPE adsorbents for the effective pre-concentration and determination of trace contaminants in water. The CMDI-1 SPE adsorbent can be easily prepared and adopted for use by water professionals in developing countries to enhance understanding on the presence and fate of such contaminants in the environment and also in technical systems, towards developing relevant environmental protection measures for sustainability.

Mycotoxins-Imprinted Polymers: A State-of-the-Art Review.

Mycotoxins are toxic metabolites of molds which can contaminate food and beverages. Because of their acute and chronic toxicity, they can have harmful effects when ingested or inhaled, posing severe risks to human health. Contemporary analytical methods have the sensitivity required for contamination detection and quantification, but the direct application of these methods on real samples is not straightforward because of matrix complexity, and clean-up and preconcentration steps are needed, more and more requiring the application of highly selective solid-phase extraction materials. Molecularly imprinted polymers (MIPs) are artificial receptors mimicking the natural antibodies that are increasingly being used as a solid phase in extraction methods where selectivity towards target analytes is mandatory. In this review, the state-of-the-art about molecularly imprinted polymers as solid-phase extraction materials in mycotoxin contamination analysis will be discussed, with particular attention paid to the use of mimic molecules in the synthesis of mycotoxin-imprinted materials, to the application of these materials to food real samples, and to the development of advanced extraction methods involving molecular imprinting technology.

Sample Preparation Techniques for Growth-Promoting Agents in Various Mammalian Specimen Preceding MS-Analytics.

The misuse of growth-promoting drugs such as beta-2 agonists and steroids is a known problem in farming and sports competitions. Prior to the analysis of biological samples via liquid chromatography (LC)-mass spectrometry (MS) or gas chromatography (GC)-MS, sufficient sample preparation is required to reliably identify or determine the residues of drugs. In practice, broad screening methods are often used to save time and analyze as many compounds as possible. This review was conceptualized to analyze the literature from 2018 until October 2023 for sample preparation procedures applied to animal specimens before LC- or GC-MS analysis. The animals were either used in farming or sports. In the present review, solid phase extraction (SPE) was observed as the dominant sample clean-up technique for beta-2 agonists and steroids, followed by protein precipitation. For the extraction of beta-2 agonists, mixed-mode cation exchanger-based SPE phases were preferably applied, while for the steroids, various types of SPE materials were reported. Furthermore, dispersive SPE-based QuEChERs were utilized. Combinatory use of SPE and liquid-liquid extraction (LLE) was observed to cover further drug classes in addition to beta-2 agonists in broader screening methods.

Mesoporous silica imprinted nanocomposites for selective adsorption and detection of levofloxacin

The proper treatment of antibiotics has become a formidable challenge in environmental remediation. In this work, a mesoporous molecularly imprinted polymer (mMIP) was successfully fabricated on SiO2 by the sol gel process and used to selectively adsorb and detect antibiotic levofloxacin (LEVO). The adsorption characteristics of LEVO-mMIP were explored in diverse respects (e.g., kinetics, isotherms, and selectivity). The mMIP exhibited higher LEVO adsorption capacity (115 mg/g), higher specific selectivity, and faster kinetics (10 min). The prepared mMIP also exhibited enhanced reusability/durability (n = 8 cycles). The LEVO-mMIP was thus used as dispersive solid phase extraction material for the extraction of LEVO from actual samples (e.g., tap/river water and pharmaceutical formulations) with the aid of high performance liquid chromatography (LOD of 0.07 ng/mL and good recoveries of 90.76–108.17% (RSD of 2.55–5.09%)). As such, the potential utility of mMIP is validated for the adsorption and detection of LEVO in environmental matrices.

Preparation of mixed-mode weak cation exchange magnetic solid-phase extraction sorbent and its application in the extraction of 21 illicit drugs from wastewater

The detection of illicit drugs in wastewater can effectively monitor and evaluate the trend of illicit drug abuse. A novel mixed-mode cation exchange magnetic sorbent Fe3O4 @poly(ST/DVB/MA-COOH) was prepared and firstly applied as magnetically dispersed solid phase extraction material to efficiently, rapidly, and selectively extract 21 illicit drugs from wastewater. The selectivity of the sorbent was mainly attributed to the electrostatic interaction. The effects of Fe3O4 @poly(ST/DVB/MA-COOH) preparation and extraction conditions on the adsorption performance were thoroughly discussed. Among the 21 illicit drugs, the absolute extraction recovery values for 19 illicit drugs were greater than 80 % and the entire adsorption process could be achieved in one minute. Subsequently, the Fe3O4 @poly(ST/DVB/MA-COOH) sorbent combined with UHPLC-MS/MS was used to establish a quantitative method for the effectively extracted 19 illicit drugs in wastewater. The method had a good determination coefficient in the range of 0.2–200 ng/L and the limits of detection of the method were 0.03–0.67 ng/L. The spiked recovery values were in the range of 87.0–119.6 %. Finally, the method was successfully applied to the detection of 19 illicit drugs in wastewater samples and also compared with the commonly used SPE method. The obtained results indicate that Fe3O4 @poly(ST/DVB/MA-COOH) has great advantages in the detection of illicit drugs in wastewater.

Development of hydroxypropyl cellulose and graphene oxide modified molecularly imprinted polymers for separation and enrichment of podophyllotoxin

A novel hydroxylpropyl cellulose (HPC) modified graphene oxide (GO)-based molecularly imprinted polymers (HPC-GO-MIP) have been developed as a solid phase extraction (SPE) material for the selective separation and extraction of podophyllotoxin. In this strategy, the cellulose with rich hydroxyl groups was introduced to form bi-functional monomers with methacrylic acid to provide more recognition sites for the improving of extraction efficiency, then GO was added as a two-dimensional substrate for MIP to improve the material morphology and surface area. The extraction performances of obtained HPC-GO-MIP material were tested, and the results prove its high efficiency and selectivity for podophyllotoxin extraction. The saturated adsorption capacity reached 23.1 μg/mg, and high enrichment efiiciency of 463.8 folds was realized under the premise of ensuring the recovery rate. The selective imprinting factor was much higher than those of kaempferol and quercetin, which were the main compounds in podophyllum fruit. Under the optimized SPE conditions, the HPC-GO-MIP based SPE-HPLC method showed the detection limit of 14.2 ng/mL for podophyllotoxin assay. When applied to podophyllum fruit samples, the material showed excellent ability of selective separation and enrichment of podophyllotoxin, and the relative standard deviations (RSD) of intra and inter batches were less than 8.1 % and 5.7 % in real samples detection. The HPC-GO-MIP SPE method broadened the application for high multiple extraction in trace analyte samples and provided a valuable solution to improve the selective separation and detection.

Selectivity of β-Cyclodextrin Polymer toward Aquatic Contaminants: Insights from Ultrahigh-Resolution Mass Spectrometry of Dissolved Organic Matter.

Selectivity in solid-phase extraction (SPE) materials has become increasingly important for analyte enrichment in sensitive analytical workflows to alleviate detrimental matrix effects. Molecular-level investigation of matrix constituents, which are preferentially extracted or excluded, can provide the analytical chemist with valuable information to learn about their control on sorbent selectivity. In this work, we employ nontargeted Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) to elucidate the molecular chemodiversity of freshwater-derived dissolved organic matter (DOM) extracted by the selective model sorbent β-cyclodextrin polymer (β-CDP) in comparison to conventional, universal SPE sorbents (i.e., Oasis HLB, Supel-Select HLB, and LiChrolut EN). Statistical analysis of MS data corroborated the highly selective nature of β-CDP by revealing the extracted DOM spectra that are most dissimilar to original compositions. We found that its selectivity was characterized by pronounced discrimination against highly oxygenated and unsaturated DOM compounds, which were associated with the classes of lignin-like, tannin-like, and carboxylic-rich alicyclic molecules. In contrast, conventional sorbents excluded less highly oxygenated compounds and showed a more universal extraction behavior for a wide range of DOM compositional space. We lay these findings in a larger context that aids the analyst in obtaining an a priori estimate of sorbent selectivity toward any target analyte of interest serving thereby an optimization of sample preparation. This study highlights the great value of nontargeted ultrahigh-resolution MS for better understanding of targeted analytics and provides new insights into the selective sorption behavior of novel sorbents.

Self-assembled magnetic nanoplatform Fe3O4@SiO2-NH2@Au for magnetic solid-phase extraction of bisphenol A

Developing magnetic adsorbent that combines the merits of quick response, excellent enrichment capacity, uniform and stable dispersivity is of paramount importance in pollutants pretreatment. In this work, tunable strawberry-like Fe3O4 @SiO2-NH2 @Au@ 2-ME magnetic solid phase extraction materials were prepared via assembly method. The obtained nanocomposites were characterized using scanning electron microscopy, X-ray diffraction spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and whereafter the preparation method was optimized. Integrating magnetic solid-phase extraction with high-performance liquid chromatography and fluorescence detection, a comprehensive enrichment and detection method toward bisphenol A (BPA) was well established. This method demonstrated high efficiency and rapidity, achieving rapid enrichment of BPA. The as-developed method exhibited good linear correlation within the range of 10.0–500 μg·L−1, with a recovery of 85–92%. It showed excellent sensitivity and reproducibility in BPA extraction with low limit of detection (LOD, 0.274 μg·L−1), limit of quantitation (LOQ, 0.913 μg·L−1) and relative standard deviation (RSD, 1.5%, n = 6), respectively. The proposed Fe3O4 @SiO2-NH2 @Au nanoplatform firmly supports the envision that proper surface functionalization of magnetic substrate could promote the enrichment capacity toward various pollutants in actual application scenarios.

Synthesis, characterization and uptake studies of diglycolamic acid and diglycolamide analogs adsorbents for extraction of rare earth elements

Tetraalkyldiglycolamides are known for their high extracting efficiency of rare earth elements (REEs) from nitric acid solutions (1–6 mol/L). Nevertheless, solid-phase extractants based on diglycolamides (DGA) are poorly studied for REEs extraction. This paper explores the design and synthesis of novel REEs adsorbents by grafting silica with diglycolic acid-based ligands. The newly developed solid-phase materials were investigated for their potential to effectively separate REEs from various media. The functionalization of the silica with different ligands was quantified, and the adsorbents' extraction capacities and selectivity for REEs over Calcium (Ca2+), Aluminium (Al3+) and Iron (Fe3+) were evaluated. Si-NH-DGA emerged as the most efficient adsorbent for Gd3+ extraction, exhibiting a remarkable capacity of 44 mg/g at pH 4–6. However, modifications involving ether oxygen substitution with a methylamino group or sulfur led to reduced extraction efficiencies. Si-NH-DGA-NMe2 demonstrated strong binding of REEs in nitric acid solutions (1–3 mol/L HNO3) with corresponding adsorption capacities for Y3+, La3+, Gd3+ and Yb3+ being 16.3, 14.2, 22.8, and 30.2 mg/g, respectively. Furthermore, it displayed remarkable selectivity for REEs over Ca2+. The equilibrium extraction for Gd occurred within 60 min for Si-NH-DGA and Si-NH-DGA-NMe2 under their respective optimal conditions. Disodium EDTA solution demonstrated a high stripping efficiency for Gd3+ in the Si-NH-DGA-NMe2 column extraction, yielding a significant concentration factor (CF = 85). In the same column, following five cycles of loading/stripping of Gd3+, there was an average capacity loss of 6%. Si-NH-DGA-NMe2 emerged as a promising material for solid-phase extraction from concentrated nitric acid solutions, characterized by high capacity and good selectivity towards middle and heavy REEs. This structure has the potential to be further optimized for the development of a solid-phase extraction column for REEs separation and purification. The findings also highlight the potential of Si-NH-DGA-NMe2 as a candidate for REEs adsorption for potential industrial applications and the purification of acidic waste solutions.

Method development for analysis 13 per‐ and polyfluoroalkyl acids in tap water by HPLC‐MS/MS

AbstractThe purpose of this study was to develop a sensitive, accurate and simple method for analysis of 13 perfluoroalkyl acids (8 perfluoroalkyl carboxylic acids and 5 perfluoroalkyl sulfonic acids) in tap water by LC‐MS/MS. This paper focuses on optimizing the chromatographic instrumental operating parameters and the solid phase extraction conditions using HLB cartridges. Results from the method validation showed that the method has sub ng/L LOQs (0.10‐0.60 ng/L), quantitative recoveries at the concentrations near the LOQs (74.4‐122.8%) and high repeatability with acceptable %RSD (15.6‐38.3%). The analytical procedure was then applied to assess how significant the contamination of PFAAs in tap water of Ho Chi Minh City. Besides that, a new self‐made solid phase extraction material prepared by grafting an ionic liquid on silica was used to enrich the target analytes. Preliminary results show that the material based on 1‐octyl‐3‐(3‐(triethoxysilyl) propyl)‐1H‐imidazolium bromide has promising retention ability for these compounds, the recoveries on ionic liquid‐based materials ranged from 36.3‐69.0%.

Nanoscale Ion-Exchange Materials: From Analytical Chemistry to Industrial and Biomedical Applications.

Nano-sized ion exchangers (NIEs) combine the properties of common bulk ion-exchange polymers with the unique advantages of downsizing into nanoparticulate matter. In particular, being by nature milti-charged ions exchangers, NIEs possess high reactivity and stability in suspensions. This brief review provides an introduction to the emerging landscape of various NIE materials and summarizes their actual and potential applications. Special attention is paid to the different methods of NIE fabrication and studying their ion-exchange behavior. Critically discussed are different examples of using NIEs in chemical analysis, e.g., as solid-phase extraction materials, ion chromatography separating phases, modifiers for capillary electrophoresis, etc., and in industry (fuel cells, catalysis, water softening). Also brought into focus is the potential of NIEs for controlled drug and contrast agent delivery.

Method development and quantification of all B vitamins and selected biosynthetic precursors in winter and spring samples from the North Sea and de novo synthesized by Vibrio campbellii

The simultaneous analysis of B vitamins and biosynthetic precursors in seawater is of great interest as it gives a better insight into the fluctuations of their availability for marine organisms and thus allows us to better understand the nature of interactions between prototrophic and auxotrophic organisms. The analysis of these micronutrients is challenging, as they are usually present in the marine environment in minuscule quantities only. Additionally, some of them are light- and heat-sensitive which complicates their handling. To meet these circumstances, the presented sample work-up method for seawater started with a freeze-drying step for volume reduction of the sample. This shortened the duration of the subsequent solid phase extraction and resulted in an increase in recovery. When comparing three solid phase extraction materials (C18, HLB, PPL), PPL was found to be the most suitable. This method was applied for the quantification of all eleven B vitamins and six precursors in waters from the southern North Sea taken in winter and spring. Quantification was performed by LC-MS. The winter samples showed higher concentrations for nearly all analytes, in contrast to the uptake of most nutrients at the beginning of a potential algal bloom in spring and low analyte concentrations in springtime waters. In addition, the marine bacterium Vibrio campbellii, prototrophic for most B vitamins, was cultivated without the addition of B vitamins in order to measure them intra- and extracellularly during growth. In most cases, intracellular concentrations per cell decreased towards the end of the exponential growth phase, while extracellular concentrations increased. Extracellular B vitamin and precursor concentration measurements show that V. campbellii is in exchange with its environment and thereby possibly enables growth of B vitamin auxotrophs in the environment.

TiO2@ZnO nanocomposite: bifunctional material for solid phase extraction of U(VI) and Th(IV) and photocatalytic degradation of organic contaminant

TiO2@ZnO nanocomposite: bifunctional material for solid phase extraction of U(VI) and Th(IV) and photocatalytic degradation of organic contaminant

A free elution immunoassay for chloramphenicol in chicken and egg after magnetic ZIF-8 adsorption separation

The excellent adsorption and rapid separation capabilities of magnetic MOFs make them desirable pretreatment materials for solid substrates. In this study, magnetic ZIF-8 (mZIF-8) was synthesized in situ by a one-step method in the aqueous solution of magnetic beads. Isothermal adsorption verified that the maximum adsorption capacity of (011) crystal-exposed rhombic dodecahedral ZIF-8 for chloramphenicol was up to 128.31 mg/g (mZIF-8 = 67.18 mg/g). Kinetic adsorption revealed that the type of ZIF-8/mZIF-8 adsorption on chloramphenicol belongs to the pseudo-secondary adsorption kinetics of chemical monomolecular layers. Characterization by FTIR, XPS, and XRD revealed that mZIF-8 interacts with chloramphenicol mainly by π-π electron stacking, electrostatic attraction, and hydrogen bonding interaction. ELISA confirmed that chloramphenicol remained antigenically active after adsorption by mZIF-8. The adsorption and separation of chloramphenicol residues in chicken and egg were completed by mZIF-8 within 20 min. mZIF-8 can be used directly for elution-free ELISA after the adsorption of chloramphenicol. The limits of detection (IC10) of the mZIF-8 + ELISA in chicken and eggs were 1.18 ng/mL and 0.64 ng/mL, respectively. mZIF-8 is expected to be used as a magnetic solid-phase extraction material for the rapid pretreatment of antibiotic residues in other complex solid matrices.

Synthesis of a magnetic micro-eutectogel based on a deep eutectic solvent gel immobilized in calcium alginate: Application for green analysis of melamine in milk and dairy products

A new three-component magnetic eutectogel composed of a crosslinked copolymeric deep eutectic solvent (DES) and polyvinylpyrrolidone-coated Fe3O4 nano-powder impregnated in calcium alginate gel was synthesized and applied as a sorbent material in a green alternative micro solid-phase extraction of melamine in milk and dairy products. The analyses were performed using the HPLC-UV technique. The copolymeric DES was prepared through thermally-induced free-radical polymerization of [2-hydroxyethyl methacrylate]:[thymol] DES (1:1 mol ratio) as functional monomer, azobisisobutyronitrile (as initiator), and ethylene glycol dimethacrylate (as crosslinker). The sorbent was characterized using ATR-FTIR, 1H &13C FT-NMR, SEM, VSM, and BET techniques. The stability of the eutectogel in water and its effect on the pH of the aqueous solution was studied. A one-at-a-time approach was applied to optimize the impact of significant factors influencing sample preparation efficiency (sorbent mass, desorption conditions, adsorption time, pH, and ionic strength). The method validation was performed by evaluating matrix-matched calibration linearity (2–300 μg kg−1, r2 = 0.9902), precision, system suitability, specificity, enrichment factor, and matrix effect. The obtained limit of quantification (0.38 μg kg−1) was lower than the established maximum level for melamine by Food and Drug Administration (FDA) (0.25 mg kg−1), Food and Agriculture Organization (FAO) (0.5 & 2.5 mg kg−1), and The European Union (EU) (2.5 mg kg−1) in milk and dairy products. The optimized procedure was applied for the analysis of melamine in bovine milk, yogurt, cream, cheese, and ice cream. The obtained normalized recoveries of 77.4–105.3% (RSD% <7.0%) were acceptable regarding the practical default range set by the European Commission (70–120%, RSD≤20%). The sustainability and green aspects of the procedure were evaluated by the Analytical Greenness Metric Approach (0.6/1.0) and the Analytical Eco-Scale tool (73/100). This paper presents the first-time synthesis and application of this micro-eutectogel for the analysis of melamine in milk and milk-based dairy products.

Evaluation of a Resorcinarene-Based Sorbent as a Solid-Phase Extraction Material for the Enrichment of L-Carnitine from Aqueous Solutions

We present five new sorbents for the evaluation of the pre-concentration of L-carnitine. The sorbents were obtained from copolymerization between butylmethacrylate (BuMA) and ethylene dimethacrylate (EDMA), which were physically modified on their surface by each one of the five synthetized resorcinarenes of variable chain length studied, with long-chain resorcinarenes exhibiting better fixation on the copolymer. The characterization of the synthesized resorcinarenes was done using FTIR-ATR, 1H NMR, 13C NMR, and mass spectrometry, while characterization of the sorbents was done using FTIR-ATR and scanning electron micrography (SEM). The molecular interaction between L-carnitine and the synthesized resorcinarenes was studied in DMSO via 1H-NMR spectroscopy and, in the gas phase, via electrospray ionization-mass spectrometry (ESI-MS). The results showed that the short-chain resorcinarenes underwent a stable interaction with the neurotransmitter. Once the sorption of resorcinarenes on the copolymer was accomplished, the best parameters for the evaluation of the L-carnitine preconcentration were established. The solution tests were carried out through LC/MS analysis, obtaining better results for L-carnitine absorption with the short-chain resorcinarenes such as tetra(ethyl)calix[4]resorcinarene and tetra(propyl)calix[4]resorcinarene.