Desorption Volume Research Articles

Trace Extraction of Metoprolol from Plasma, Urine and EBC Samples Using Modified Magnetic Nanoparticles Followed by Spectrofluorimetric Determination for Drug Monitoring Purposes

Background: Metoprolol is a selective β1-adrenergic receptor antagonist (β-blockers). It is widely used for the treatment of hypertension and other related diseases. Metoprolol can be used as a doping agent in sports, thus has been included in the list of forbidden drugs. In Iran, therapeutic drug monitoring (TDM) of β-blockers is an applied procedure in some cases. A therapeutic regimen could be easily managed by the determination of drug levels in biological fluids which is a relatively costly process and requires highly skilled technical staff. Using a simple and low-cost analytical procedure may help to use TDM in routine clinical practice. Methods: A real biological sample was prepared and its pH was adjusted to 3-4, then metoprolol was quickly extracted using magnetic iron oxide nanoparticles (MIONPs) modified by sodium dodecyl sulfate (SDS) and determined by applying spectrofluorimetry at 340 ± 3 nm after excitation at 283 ± 3 nm. Results: The extraction and determination conditions including, the amount of MIONPs and SDS, pH of the solution, standing time, desorption solvent type and volume were investigated and adjusted. Calibration curves were linear over the concentration range of 6–100 ng/mL for plasma and 5–100 ng/mL for water, urine and exhaled breath condensate samples, respectively. Intra and inter-day precision values for determination of metoprolol in different samples were less than 5.6 % and 6 %, respectively, and accuracy (as a relative error) was better than 5 %. Moreover, standard addition recovery tests were carried out, and the analytical recoveries ranged from 86 % to 113 %. The limits of detection (LOD) and limits of quantification (LOQ) of metoprolol were found to be in the range of 2.1-3.4 ng/mL and 6.3- 10.2 ng/mL, respectively. Conclusion: The developed method was successfully applied to biological samples taken from a volunteer who was given an oral tablet of 50 mg metoprolol.

Combination of magnetic solid‐phase extraction with dispersive liquid–liquid microextraction followed by GC‐MS for trace analysis of synthetic cannabinoids in plasma samples

In this work, an efficient extraction method based on a combination of magnetic solid-phase extraction (MSPE) and dispersive liquid–liquid microextraction (DLLME) followed by GC-MS was developed for the determination of 5F-ADB-PINACA (ADB) and AB-FUBINACA (AB). Fe3O4 nanoparticles coated with poly ortho-aminophenol were synthesised and applied as the sorbent. Extraction parameters including pH in both the MSPE (pH 3.5) and DLLME (pH 11) steps, sorbent amount (20 mg), salt effect (10%, w/v), adsorption (20 min) and desorption time (5 min), type and volume of eluent (1.0 ml of acetone) and extraction solvent (25 µl of toluene), were optimised. Enrichment factors of 213 and 437 obtained for ADB and AB, respectively. The linear ranges of the method were obtained 0.2–50 and 0.2–50 ng ml−1 for ADB and AB, respectively. Regression coefficients above 0.998 and LODs of 0.01 and 0.005 ng ml−1 resulted. The intra- and inter-day RSDs% (n = 3) were found to be 8.3 and 7.6%, respectively. Finally, MSPE-DLLME-GC/MS was applied for the determination of analytes in plasma samples. Recoveries were within the range of 87.6–102.6 and 89.4–104% for the ADB and AB, respectively, indicating the suitability of the proposed method for analysis of ADB and AB in complicated matrices.

Spherical conjugated microporous polymers for solid phase microextraction of carbamate pesticides from water samples.

Conjugated microporous polymers (CMPs) with uniform morphology have shown fascinating application in the separation science. In this study, metal-free Knoevenagel condensation was adopted to prepare spherical sp2 carbon-conjugated microporous polymers, which used tetrakis(4-formylphenyl)methane and 1,4-phenylenediacetonitrile as monomers. Due to the remarkable extraction capability for carbamate pesticides (CPs), the as-synthesized CMPs were fabricated as the coating for solid-phase microextraction (SPME). After optimized SPME parameters (adsorption time, salt concentration, sample pH, adsorption temperature, desorption time, desorption solvent and desorption volume), ten CPs in water samples were quantified by ultrahigh performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Linearity in the range 0.005-100ng mL-1 with low detection limits of 0.00060-0.017ng mL-1 was obtained. The intra-day and inter-day precisions expressed as relative standard deviations were 1.5-8.1% and 1.1-8.0%, respectively. Fiber-to-fiber reproducibility was below 7.3%. The CMPs-SPME-UPLC-MS/MS method was applied to detect trace CPs in real water samples with relative recoveries from 91.8% to 108%.

Monodisperse pillar[5]arene-based polymeric sub-microsphere for on-line extraction coupling with high-performance liquid chromatography to determine antioxidants in the migration of food contact materials

The monodisperse pillar[5]arene-based polymeric sub-microsphere was prepared by polycondensation of hydroxylated pillar[5]arene and cyanuric chloride through a one-pot reaction in mild condition. The preparation was realized by a simple two-step temperature-programmed process without heating operation. The obtained polymeric sub-microsphere exhibited monodisperse and regular spherical structure with uniform particle size distribution of 220–320 nm accounting for 94%. The prominent adsorption capacity of the polymeric sub-microsphere for antioxidants was demonstrated and attributed to the synergistic effect of the cladding interaction with the π-electron rich cavity and hydrophilic interaction with terminal hydroxyl on pillar[5]arene. Then the pillar[5]arene sub-microsphere was packed into a micro-column to realize effective on-line enrichment of antioxidants coupling with high-performance liquid chromatography (HPLC). The flow rate of extraction and desorption solvent, clean-up and desorption volume were assessed to optimize the method. The method showed wide linear ranges with R2 greater than 0.9926, low limits of detection (0.030–0.20 μg/L) and limits of quantification (0.10–0.67 μg/L). The developed method was successfully applied to determine trace antioxidants in the migration of food contact materials with simulated solution, which demonstrated the promising potential of this method for practical analysis. Furthermore, the migration behavior of antioxidants from food packaging materials into different food matrix was also investigated.

In situ growth of metal-organic framework HKUST-1 in an organic polymer as sorbent for nitrated and oxygenated polycyclic aromatic hydrocarbon in environmental water samples prior to quantitation by HPLC-UV.

An in situ preparation of metal-organic framework (HKUST-1) on the surface of an organic polymer is reported. The hybrid material was evaluated as sorbent for solid-phase extraction (SPE) of oxygenated and nitrated polycyclic aromatic hydrocarbons (PAHs). The growth of HKUST-1 on MAA-based polymer was accomplished using a layer-by-layer assembly strategy. The HKUST-1-polymer was characterized using powder X-ray diffraction and scanning electron microscopy to demonstrate the incorporation of MOF crystals onto the polymer surface. The MOF (nano)crystals were characterized using high-resolution transmission electron microscopy and high-angle annular-dark-field scanning transmission electron microscopy. The water-stable MOF-polymer was evaluated as SPE sorbent, and several variables that can influence the extraction recoveries of PAH derivatives were investigated. Under the selected conditions, the detection limits varied between 4 and 21ng·L-1, and the precision (relative standard deviation) was below 12%. The recovery values for spiked solutionsranged from 95 to 104%, and the enrichment factor achieved was close to 1000-fold using a high sample volume (100mL) and very low desorption volume (100μL). The SPE enrichment combined with HPLC and DAD detector was successfully applied to the extraction and determination of polycyclic hydrocarbons in environmental water samples. Graphical abstract A layer-by-layer synthesis of HKUST-1 onto polymer surface was performed and applied to isolation of PAH derivatives in environmental water samples.

Sensitive determination of urinary muconic acid using magnetic dispersive-solid-phase extraction by magnetic amino-functionalised UiO-66

ABSTRACT In this study, a magnetic-dispersive solid-phase extraction (DSPE) was developed for the extraction and desorption of muconic acid from real urine sample. For this purpose, Fe3O4-SiO2-NH2@ UiO-66 was used as a Metal-Organic Framework (MOF) in the DSPE for extraction of the analyte of interest followed by High-Performance Liquid Chromatography (HPLC) analysis. The synthesised magnetic-MOF was characterised by XRD, VSM, FT-IR, and FE-SEM techniques. The experimental parameters influencing the magnetic-DSPE procedure, such as solution pH, initial sample volume, extraction and desorption time, type and volume of elution solution, and sorbent amount were examined. Under the optimal conditions, the UiO-magnetic DSPE-HPLC procedure provided a good limit of detection (0.001 µg mL−1), the limit of quantification (0.003 µg mL−1), wide linear dynamic range (0.003–25 µg mL−1) and high correlation coefficient (r2: 0.997). Also, the Fe3O4- SiO2- NH2@ UiO-66 exhibited an acceptable accuracy (2.0–4.0%), reproducibility (3.7–6.1%), and per cent recovery (96–98%) for the extraction and desorption of the desired analyte. It can be concluded that the proposed method was efficient for the extraction and analysis of muconic acid from real urine samples. Therefore, the Fe3O4- SiO2- NH2@ UiO-66 – DSPE-HPLC method can be used as a simple, fast, sensitive, reusable, and user-friendly extraction technique to determine trace levels of urinary muconic acid.

Gas transport through coal particles: Matrix-flux controlled or fracture-flux controlled?

In laboratory measurements, methane ad-/de-sorption behavior on coal is known to be directly related to the particle size. As expected, coal exhibits a relatively high initial desorption rate for smaller coal particles which results in a different gas desorption volume and pressure curves from platter ones for larger coal particles. Both fracture-dominated and matrix-dominated flow theories had been proposed to explain the difference in shapes of desorption curves. These two theories, however, are contradictory to each other and neither of them is completely convincing. Based on the newly developed relationship of apparent diffusion coefficient and apparent permeability, this work uses a dual-permeability concept to explain the different shapes of desorption curves. Numerical simulation solutions indicate that the switching dominance of the fracture and matrix permeability systems produces variable desorption curve shapes. With continuing decrease of coal particle size, the flow will gradually change from fracture-dominated to matrix-dominated mode. The critical apparent permeability ratio dividing the domination of these two systems is in the order of ~10−2, in contrast to the initial hypothesis that if one system dominates the overall gas flow, its permeability must be smaller than that of the other. As particle radius decreases, this parameter first increases and then remain at a certain value. At last, the simulated desorption curves were validated with laboratory desorption experimental data.

Study on desorption and diffusion dynamics of coal reservoir through step-by-step depressurization simulation——an experimental simulation study based on LF-NMR technology

Pressure dropping control is one of the key technologies for coalbed methane surface development. Low-field nuclear magnetic resonance (LF-NMR) technology was adopted to study methane diffusion and pore dynamics of various pressure drop procedures. Calibration, isothermal desorption, pressure step-down desorption, and pore dynamic experiments were conducted with high-rank coal samples. The results include the following four aspects. 1) Calibration experiments of methane content and LF-NMR T2 spectrum in confined cylindrical coal samples show that adsorbed, porous medium-confined and bulk methane can be distinguished and quantitatively calculated using LF-NMR technology. 2) According to the desorption equation fitting using LF-NMR technology, ultimate desorption volume at different stages of depressurization is calculated and the overall desorption process has been divided into inefficiency, slow, rapid, and sensitive stage. 3) LF-NMR desorption experiments with constant confine pressure show that cumulative desorption volume of two and three step-down pressure reductions are higher than that of one-step and uniform pressure reductions. Synchronisation of rapid or sensitive desorption stage and large effective diffusion coefficient (De) are keys to achieve a high cumulative gas production. 4) De varies significantly along with the variation of equilibrium gas pressure at the inefficiency and slow desorption stage, which is mainly affected by the surface coverage. Stress compression and matrix shrinkage coupling influence the pore structure at rapid and sensitive stage, thereby on De. The different desorption results using various depressurization schemes are the reason that pore deformation behaviour causing dynamic variation of the diffusion process. The above results can provide a basis for optimising the drainage work of coalbed methane.

Pore morphology characterization and its effect on methane desorption in water-containing coal: An exploratory study on the mechanism of gas migration in water-injected coal seam

Water-injected technique was once considered as an effective way to solve the gas-induced problems in the mining industry, but has been stagnant due to its unstable conditions. A systematic knowledge on the micro-mechanism of water injection into coal seams is beneficial to better understand water-based techniques. However, the laboratory investigations considering the engineering background of water injection as well as the pore morphology of targeted coal seam have been rarely studied. In this paper, characterization of pore morphology and the effect of injected water on gas desorption characteristic were carried out using pore structure analyzers (N2 adsorption and mercury intrusion methods), high-resolution scanning electron microscopy and a home-made instrument (water-injecting desorption test). The pore morphology results from pore size distribution, fractal dimension, pore shape and connectivity indicate that the essential configuration of pore structure is well-developed larger pores containing abundant smaller pores with extensive distribution of constricted pores that are inaccessible to fluid migration. The influence of pore morphology on desorption process may be attributed to the microporous constrictions with non-effective pores, which are geometrically interpreted by pore blocking mechanism. The desorption test results show the total desorption volumes and initial effective diffusion coefficient have the reduce rates of 26.65% and 38% with the moisture content increasing from dry to 1.8% while have a little change as moisture increases (1.8%–11.2%), demonstrating the obstruction of water molecule on gas desorption pathway and the existence of extremity moisture content. Water injection has a remarkable effect on the average desorption rates in the initial period of 10 min; however, the ultimate desorption volume of 0.81 mL/g with higher moisture content of 11.2% is not sensitive to adsorption equilibrium pressure. Moreover, combined with the mature water-injected technique in the actual coal seam, a conceptual design was summarized to consider the effect of the constricted pore morphology on the interactions of “water-gas-coal”, which may demonstrate the micro-mechanism of gas migration in the far water-injected coal seam. Meanwhile, in the near water injection zone, due to more energetic gas molecules forming gas bubble in the aqueous condition, nucleation appears to be imagined to explain the pressure-insensitive phenomenon. These findings are of great guiding significance to the theoretical studies and field applications of actual water-injected coal seam.

Variation in permeability during CO2–CH4 displacement in coal seams: Part 1 – Experimental insights

The injection of CO2 into deep coal seams can improve the recovery of CH4 and contribute to the geological sequestration of CO2. To reveal the controlling factors associated with CO2 displacing CH4, experiments were conducted to simulate the process under different confining pressures (8, 12, 16, and 20 MPa) and CO2 injection pressures (1–6 MPa). The results show that coal can adsorb more CO2 than CH4. However, the permeability of CH4 is greater than that of CO2 under inlet gas pressures of 1–5 MPa. For CH4 saturated coals, the CH4 desorption volume is higher under CO2 displacing conditions compared to pure CH4 desorption processes under the same pressures. The coal adsorbed CO2 decreases under high pore and confining pressures, indicating the displacement results may be better in shallow buried coals. The axial, radial, and bulk strains of coal show steady, sharp, and then slow declining trends with decreasing pore pressures, and the inflection points generally occur at 5.25 and 3.25 MPa. Meanwhile, the strain in three directions decreases exponentially with the increase of effective stress, and the radial strain is higher than the axial strain under each confining pressure. With the combined influences of effective stress, matrix swelling/shrinkage, and gas slippage, the permeability decreases first and then increases with the decrease of pore pressure. With the decrease of pore pressure and the increase of confining pressure, the combined influence of the three factors on coal permeability gradually weakens. The results would be beneficial for controlling the injection process and permeability variation predicting during CO2 sequestration and the replacement of CH4 in coals at different burial depths.

Laboratory measurements of methane desorption behavior on coal under different modes of real-time microwave loading

This paper presents a technique for accelerating coalbed methane (CBM) desorption to increase extraction efficiency using microwaves. Methane desorption experiments with and without real-time microwave loading (ML) were carried out in the laboratory. To avoid high temperatures in the samples, ML was employed via two modes; continuous ML (CML) with low power and discontinuous ML (DML) with high power. The results show that total desorption volumes were increased from 1.87 to 3.26 times under CML and from 1.91 to 4.13 times under DML. The desorption rate using CML decreased smoothly like the rate without ML but the desorption rate was higher. The DML caused the desorption rate to increase rapidly and sharp peaks were evident on its desorption rate graph. For DML, the maximum desorption rate increased by a factor of 10.8. Kinetic analysis indicated that both CML and DML increased the diffusion coefficient and reduced diffusion attenuation. For the same microwave output energy, DML with short-term microwave bursts with high power has a better stimulating effect on methane desorption than CML. That ML significantly enhances methane desorption indicates that ML can greatly improve CBM productivity, and thus it has the potential to become a new CBM stimulation technology.

Effects of particle mixing on characteristics of gas desorption and non-constant dynamic diffusion in coal

ABSTRACT Gas drainage technology is closely related to the flow of methane in coal. Desorption and diffusion of gas in coal is an important basic research area, and particle size is one of the influencing factors. In this study, the desorption and diffusion characteristics of coal samples mixed with different particle sizes over time were measured under constant temperature and pressure. The results show that in the initial stage, the desorption volume and desorption rate of coal samples are relatively large. The improved desorption model can well fit the data and the order of desorption volume is negatively correlated to the mean particle size of coal samples. The single small particle coal sample has the largest desorption volume which reached 3.77ml/g. Both the unipore model and the constructed unsteady dynamic diffusion model can well describe the diffusion of gas in coal, the diffusion coefficient of coal sample decreases with time, and the decay rate decreases gradually with time until it remains unchanged. The calculation results of the two models show that the diffusion coefficient ranges of gas in coal between 10−10m2/s and 10−12m2/s. For single-particle coal samples, the diffusion coefficient is positively correlated with particle size. The diffusion coefficient D is affected by the particle size and the degree of compaction between coal particles. These observations indicate that coal samples with different particle sizes will affect the desorption and diffusion of gas, and it has a positive impact on methane recovery.

Magnetic solid-phase extraction and a portable photocolourimeter using a multi-colour light emitting diode for on-site determination of nitrite

In this study, a new, simple, cheap, fast method for on-site determination of trace amount of nitrite in atmospheric liquids and surface water is suggested. The proposed method is based on a combination of magnetic solid phase extraction with a designed portable photometer based on light-emitting diodes. The colour reaction of nitrite was carried out with 4-nitroaniline in acidic medium and then coupled with naphth-1-ol in alkaline medium to form an azo product. The reaction and extraction conditions (e.g., acidity for diazotization and alkalinity for naphth-1-ol coupling, and other reagent concentrations, amount of sorbent, desorption solvent type and volume, etc.) were optimized. Under the optimal conditions, the calibration graph was linear in the range of 0.01–0.3 mg L−1 with the limit of detection (LOD) of 0.0013 mg L−1. The enhancement factor was about 110. Relative standard deviations (RSDs) for the extraction of 0.03 and 0.1 mg L−1 of nitrite were obtained 2.49% and 5.34% for five replicates, respectively. The proposed method was able to analyse nitrite ion in water samples with satisfactory recovery ranged from 87% to 103%.

A high throughput approach to rotating-disk sorptive extraction (RDSE) using laminar cork for the simultaneous determination of multiclass organic micro-pollutants in aqueous sample by GC-MS

In this study, a high throughput approach to rotating-disk sorptive extraction (RDSE) using laminar cork as extraction phase is demonstrated for the first time in the determination of 20 multiclass organic micro-pollutants including pesticides, PAHs and UV filters compounds from aqueous samples with gas chromatography mass spectrometry (GC-MS). The influencing parameters (desorption solvent, volume and time, extraction time and sample pH and ionic strength) were carefully optimized using multivariate designs. The optimal conditions were 10 min for extraction using 35 mL of water samples and a liquid desorption using 1 mL of MeOH:AcOEt (50:50% v/v) for 20 min. A low-cost apparatus that allows six extractions simultaneously, providing a high throughput of 5 min per sample turnaround times, considering the sample preparation step was used for the first time in this modified RDSE methodology. Satisfactory analytical performance was achieved with limits of detection (LOD) between 0.08 and 1.5 μg L−1 and limits of quantification (LOQ) between 0.3 and 4.8 μg L−1. The relative recoveries for the analytes were determined using river and lake water samples spiked at different concentrations and ranging from 80% to 119% for all analytes, with relative standard deviations (RSD) lower than 20%. The extraction efficiency obtained for the proposed configuration with laminar cork was significantly superior to powdered cork, demonstrating an interesting new configuration for new applications.

Magnetic molecularly imprinted polymers prepared by reversible addition fragmentation chain transfer polymerization for dispersive solid phase extraction of polycyclic aromatic hydrocarbons in water

Magnetic molecularly imprinted polymers (MMIPs) combine nanotechnology and molecular imprinting technology to offer selective and tunable enrichment for water analysis. In this paper, a selective sorbent was prepared by surface polymerization onto magnetic Fe3O4@SiO2 nanoparticles through reversible addition fragmentation chain transfer (RAFT) polymerization. The MMIPs were used for dispersive solid phase extraction (DSPE) of 16 PAHs as priority pollutants in aqueous matrices. After preconcentration, the analysis was performed using gas chromatography with an atmospheric pressure chemical ionization-tandem mass spectrometry (APGC–MS/MS). The extraction method is based on the dispersion of MMIPs in an aqueous sample using an ultrasonic bath which provides rapid equilibrium of analytes between the sorbent and sample solution. The enriched analytes were retrieved by collecting MMIP particles and desorbed into an organic solvent before instrumental analysis. A design of experiment (DOE) approach was applied to optimize several extraction parameters including the mass of MMIPs, the sample volume, salt addition, collection time, desorption volume, and desorption time. A fractional factorial design (FFD) (26-2) was performed to assess the influence of the selected factors on the extracted amount of analytes. The most effective factors including the mass of MMIPs, the volume of sample solution, and salt content was further investigated using central composite design (CCD) and yielded quadratic models between dependent and independent variables. The optimum conditions of DSPE obtained by desirability function (DF) were employed for preconcentration of PAHs in water samples. The evaluation showed that the MMIPs provide higher extraction efficiency compared to nanoparticles such as Fe3O4, Fe3O4@SiO2 and non-imprinted polymer, demonstrating the creation of selective recognition binding sites at the surface of magnetic nanoparticles. The LODs and LOQs ranged from 1 to 100 pg mL−1 and 2 to 200 pg mL−1, respectively. Finally, the MMIP-DSPE method was successfully applied for preconcentration and trace quantification of PAHs in real samples such as produced water and river water samples.

Polymer phase transition characteristics coupled with GC-MS for the determination of phthalate esters.

Phthalate esters are easily released from plastics materials and migrate into the soil and water environment, causing serious pollution and posing a great threat to the health of human beings. A novel temperature-sensitive extractant combined with liquid-liquid microextraction was developed to preconcentrate three phthalates in the water environment. To optimize the extraction efficiency for the three phthalate esters, various parameters, including polymer molecular weight, salt type, salt addition, adsorption time, desorption solvent, desorption volume, and desorption time have been studied. Under optimal conditions, limits of detection and limits of quantification were in the range of 0.007-0.120and 0.021-0.350µg/L, respectively. Linearities varied in the range of 5-1000 µg/L, with the correlation coefficients of 0.9867-0.9997. The preconcentration factors were in the range of 25-75. The relative recoveries of the three phthalate esters were in the range of 82.2-105.6% at the spiked levels. The relative standard deviations were in the range of 0.7-9.2% based on triplicate measurements. The results indicate that the temperature-sensitive material is a good extractant for phthalate esters in water samples.

One‐step synthesized magnetic MIL‐101(Cr) for effective extraction of triazine herbicides from rice prior to determination by liquid chromatography‐tandem mass spectrometry

The magnetic metal-organic framework MIL-101(Cr) material-based solid-phase extraction method coupled with high-performance liquid chromatography and tandem mass spectrometry was applied to extract seven triazine herbicides in rices. Fe3 O4 /MIL-101(Cr) was synthesized using reduction-precipitation method, in which steps including pre-synthesis and modification of Fe3 O4 nanoparticles were by-passed. Various parameters including extraction solvent type and volume, ultrasonic extraction time, amount of Fe3 O4 /MIL-101(Cr) microspheres, adsorption time, desorption volume and time were investigated. Under optimal conditions, the proposed method had the limit of detection (S/N=3) and the limit of quantification (S/N=10) of 1.08-18.10 and 3.60-60.20 pg/g, respectively. Relative standard deviations calculated for all herbicides with concentrations of 2 and 20ng/g were in the range of 0.5 to 13% (n=3). In addition, at the two above-mentioned concentrations, the method achieved relative recoveries percentages of 79.3 to 116.7% when applied to determine the triazine herbicides in real samples spiked. This rapid, green, non-polluting, pre-concentrated extraction method was successfully developed and applied to analyze herbicides in rice samples.

Synthesis of magnetic nanoparticles to detect Sudan dye adulteration in chilli powders

Magnetic nanoparticles were synthesised to extract Sudan dyes from chilli powders. The adsorbents used were magnetic ferroferric oxide nanoparticles coated with polystyrene. The extraction procedures for Sudan dyes comprised liquid-solid extraction and magnetic solid phase extraction. The conditions were optimised to achieve efficient magnetic solid phase extraction, including extraction and desorption time, type and volume of the desorption solvent, and the mass of the adsorbents. Repeatability tests showed satisfactory recovery rates of 80.2–115.8%, with a relative standard deviation <3.8%. The results suggested that the proposed extraction method was effective and efficient to extract Sudan dyes from chilli powders. The extraction process was simpler compared with traditional approaches because the adsorbents can be rapidly removed from the sample matrix using a permanent magnet. The use of recyclable adsorbents decreased the cost greatly. Chilli powder samples collected from local markets in Singapore were tested using the proposed method under optimum conditions.

Amine modified magnetic polystyrene for extraction of drugs from urine samples

Polystyrene is one of the best candidates as the extracting medium due to its high stability in different media and acceptable extraction capability. However, the hydrophobic nature and low wettability of polystyrene limits its application to non–polar analytes. To resolve this limitation, in this project, amine groups were chemically attached to the surface of magnetic polystyrene. The resulting hydrophilic magnetic particles were expected to be capable of extracting both polar and non–polar analytes. Non–steroidal anti–inflammatory drugs (NSAIDs) were chosen for testing the applicability of modified magnetic polystyrene according to the importance of their analysis and also their wide polarity range. Major parameters associated with the extraction procedure were optimized using central composite design (CCD) method and pH 3, extraction time of 15 min, desorption volume of 350 μL and desorption time of 4 min were chosen as optimized values. Under these conditions, figures of merit were calculated including: linear dynamic range (0.5–1000 μg L−1), linear equation and limits of detection (0.1–3 μg L−1). To investigate the method precision, inter–day, intra–day and synthesis–to–synthesis relative standard deviation (RSD) were studied (<12%). All studies were conducted using blank urine samples spiked with aspirin, salicylic acid, ibuprofen, diclofenac and mefenamic acid. Naproxen was chosen as the internal standard and high–performance liquid chromatography–UV–Vis (HPLC–UV) was employed for the subsequent determination after extraction. To evaluate the applicability of the method for real sample analysis, urine samples from patients under treatment were analyzed and acceptable results were obtained. The aminated magnetic polystyrene revealed superior extraction efficiency, much higher than polystyrene before functionalization. In addition, hospital wastewater sample was tested and acceptable extraction efficiencies were obtained.

Direct Coupling of Dispersive Extractions with Magnetic Particles to Mass Spectrometry via Microfluidic Open Interface.

Microextraction coupled to mass spectrometry (MS) has great potential in analytical chemistry laboratories operating in a variety of fields. Indeed, microextraction methods directly coupled to MS can be of large value given that they can provide not only analyte extraction and enrichment but also effective sample cleanup. In recent years, the practicality in handling high active surface area, versatility, and environmentally friendly features of magnetic dispersive microextraction technologies has contributed to an explosion in the number of methods and technologies reported in the literature for a wide range of applications. However, to the best of our knowledge, no technology to date has been capable of efficiently merging these two rising concepts in a simple and integrated analytical workflow. In this context, the microfluidic open interface is presented for the direct coupling of dispersive magnetic extraction to mass spectrometry. This technology operates under the concept of a flow-isolated desorption volume, which generates a stagnant droplet open to ambient conditions while continuously feeding the ionization source with solvent by means of the self-aspiration process intrinsic of the electrospray ionization (ESI) interface. To improve the efficiency of the final analytical workflow, a novel dispersive magnetic micro- and nanoparticle extraction protocol for biofluid droplets was developed. The final methodology entailed the dispersion of a small amount of magnetic particles (20-70 μg) in a droplet of biofluid (≤40 μL) for extraction, followed by a particle collection step using a homemade 3D-printed holder containing an embedded rare-earth magnet. In the final step, the holder is set on top of the microfluidic open interface (MOI) for desorption in the isolated droplet. Switching the valve transfers the desorbed analytes to the ESI source in less than 5 s. As proof of concept, the completely new setup was applied to the determination of prohibited substances from phosphate-buffered saline (PBS) and human urine using Fe2O3 magnetic nanoparticles (50 nm) functionalized with C18. The limits of quantitation (LOQs) obtained were in the low-ppb range in all cases, and acceptable precision (≤20%) and accuracy (80-120%) were attained. Also, taking advantage of the fast extraction kinetics provided by the radial diffusion associated with small particles, we employed the methodology for the selective extraction of phosphopeptides from 40 μL of tryptic β-casein digest using 70 μg of magnetic Ti-IMAC microparticles. To conclude, the technology and methodology herein presented provided excellent capabilities comparable to those of other solid-phase microextraction (SPME-MS) approaches while dramatically minimizing the amount of sample and sorbent required per analysis, as well as affording significantly fast extraction times due to the enhanced kinetics of extraction.