Efficient Preconcentration Research Articles

Zn/Al-layered double hydroxide–graphene oxide nanocomposite use in the solid-phase extraction–preconcentration and HPLC determination of diclofenac

A rapid and inexpensive hydrothermal process was employed for the synthesis of a nanocomposite composed of zinc/aluminum-layered double hydroxide with carbonate interlayer anions and graphene oxide (Zn/Al LDH-GO). Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller area analysis, and X-ray diffraction technique were employed for the characterization of the prepared nanocomposite. Considering the possible cooperative adsorption effect of LDH and GO moieties, a column packed with this adsorbent has been used, for the first time, in the solid-phase extraction (SPE) of diclofenac. The analysis of DCF was carried out by employing high-performance liquid chromatography (HPLC). The parameters influencing the SPE and elution processes were optimized by the univariate sequential optimization procedure. Under optimized experimental conditions, the linear calibration plots for the determination of DCF in hospital wastewater and human serum samples were obtained in the ranges of 1–730 µg L−1 (R2 = 0.999) and 4–625 µg L−1 (R2 = 0.998), respectively. The limits of detections were correspondingly 0.12 and 0.5 µg L−1, with the preconcentration factors of 68 and 59. The column stability was excellent, and its efficiency was almost constant, even after 192 adsorption/desorption cycles. The results confirmed the abilities of the developed method for the efficient preconcentration and thus precise trace analysis of DCF in real samples.

Comparative Insight into the Performance of Two Different Amine‐Functionalized CNTs for the Chemical Speciation of Chromium

AbstractPersistent industrial activities have led to an increase in the chromium content in environmental water bodies. The accurate quantification of trace chromium species such as Cr(III) and Cr(VI) is crucial as Cr(VI) can exhibit toxicity even at sub‐ppb levels. We report herein a comparative chromium speciation study using two chemically functionalized nanoadsorbents and determination with hyphenated flow injection‐flame atomic absorption spectrometry (FI‐FAAS). The most efficient preconcentration performance was obtained by optimizing the chemical and hydrodynamic parameters. Cr(VI) concentration was ascertained by the reduction to Cr(III) as the nanoadsorbents were selective for Cr(III) adsorption only; thus, speciation was achieved. The method was selective for Cr(III) in the presence of interfering matrix components. Preconcentration factor >90 and detection limit <0.11 μg L−1 were obtained for both the nanoadsorbents (%RSD∼1.0 %). The adsorption capacity of CNT‐TYR and CNT‐ASA was found to be 42.0 and 43.2 mg g−1, respectively. The application of the proposed method to contaminated water samples gave recoveries >95 %. The accuracy of the method was verified using NIST SRM 1640a.

Efficient pre-concentration of As(III) in food samples using guanidine-modified magnetic mesoporous silica

An efficient magnetic mesoporous structure was designed and prepared for the facile pre-concentration of As(III) ions. To prepare the sorbent, core–shell magnetic silica nanoparticles were covered by MCM-41 like structure and then the surface was modified by guanidine via an amine linker (GA-MSMP). The prepared adsorbent was investigated as an effective and sensitive material for the adsorption of arsenic ions from the aqueous solution by applying a normal batch method. The imperative variables of the adsorption were studied to increase efficiency. The dynamic and static processes were tested that matched a pseudo-second-order of kinetic model and the Langmuir isotherm model, respectively. The sorbent reusability was investigated and it was confirmed that the designed product could be applied at best for six cycles successively without any significant efficiency losing. The synthesized product was tested to determine and pre-concentrate trace amounts of arsenic ions in rice and natural waters as a real sample. A desorption process applying 5 mL of hydrochloric acid (0.5 mol L−1) as an eluent, exhibited about 98% recovery of the As(III) ions adsorbed on the GA-MSMP sorbent. The maximum adsorption capacity of the GA-MSMP was calculated to be 312 mg g−1 for adsorption of As(III) under the optimal conditions.

Gold nanoparticle conjugated magnetic beads for extraction and nucleation based signal amplification in lateral flow assaying

Analogues and interferents present in complex matrices like blood, plasma or serum influence lateral flow assay (LFA) responses, resulting in weak signals which compromise the limit of detection. Herein, we report a gold nanoparticle conjugated magnetic bead (GMB) based LFA approach for extraction and sensitive visual assaying of proteins in plasma. To validate the approach GMB, conjugated with anti-Troponin I antibodies, is used to capture cardiac marker Troponin I-C-T (cTnICT) in plasma that subsequently flows through on LFA membrane via a test zone containing anti-Troponin C antibodies. The capture of cTnICT-GMB complexes at the test zone produces a characteristic brownish band, enabling concentration dependent visual detection of cTnICT. Subsequently, contrast of these bands are enhanced by a nucleation approach, that utilizes the gold nanoparticles on GMB in the test bands as seed materials for growth of more visible gold clusters, improving visual detection limit of the assay to 0.1 ng/mL in plasma within 20 min, using low sample volumes (<100 μL). The proposed approach exploits the dual functionality of GMBs for efficient preconcentration and facile signal amplification. This assay offers a promising avenue for sensitive detection of analytes in complex matrices at clinically relevant concentrations without requiring tedious sample pre-treatment protocols.

Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices.

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.

Trapping and preconcentration of volatile organic sulfur compounds in water samples by portable and battery-powered trapping device prior to gas chromatography-sulfur chemiluminescence determination

A simple, portable and battery-powered trapping device (iTrap) consisting of a purification tube, a trapping unit and a miniature air pump was developed for the pre-concentration of volatile organic sulfur compounds (VOSCs). The tested VOSCs, including methanthiol (MT), ethanethiol (ET), dimethyl sulfide (DMS), diethyl sulfide (DES) and dimethyl disulfide (DMDS), were firstly purged from water samples and then in situ pre-concentrated with the iTrap prior to their analysis by thermal desorption gas chromatography coupling with a sulfur chemiluminescence detector (TD-GC-SCD). Twenty-six adsorbents were studied to find the most suitable adsorbent for the efficient pre-concentration of VOSCs. Under optimal conditions, limits of detection of 6, 8, 6, 2 and 3 ng L−1 were obtained for MT, ET, DMS, DES and DMDS, respectively. The precisions were better than 5.3% (relative standard deviations, RSDs). The iTrap was successfully applied for the analysis of VOSCs in Certified Reference Materials, several surface water, underground water and wastewater samples collected from Pengzhou city, Sichuan, China. Moreover, the VOSCs trapped in the iTrap were much more stable than those directly stored in water samples and the recoveries for all samples could be maintained at acceptable levels (>73%), even their preservation time as long as 8 h.

Studying the effect of an ionic liquid on cloud point extraction technique for highly efficient preconcentration and speciation analysis of tellurium in water, soil and sediment samples

A simple, novel and highly sensitive ionic liquid-assisted cloud point extraction (IL-CPE) and preconcentration method was developed for the determination and speciation analysis of tellurium, using 1-octyl-3-methylimidazolium chloride as an additive for improving the extraction efficiency of Triton X-114. The Te(IV) species was complexed with ammonium pyrrolidine dithiocarbamate, extracted into the micellar IL/surfactant phase and then directly measured by electrothermal atomic absorption spectrometry (ETAAS). The total Te concentration was obtained after a pre-reduction step and Te(VI) concentration was calculated as the difference between total Te and Te(IV). Several parameters, including the type and concentration of IL and surfactant, time and temperature of the IL-CPE procedure and ETAAS conditions were thoroughly evaluated and optimized. In addition, the action mechanism of the IL on CPE was studied by fluorescence measurements using Laurdan as a polarity probe. The decrease in the internal polarity caused by the incorporation of the IL into the micelles was responsible for the improvement in the extraction efficiency. Under the optimized conditions, a sensitivity enhancement factor of 87 and an extraction efficiency of 90% were achieved. Limits of detection of 1.1 and 1.7 ng L−1 and relative standard deviations of 3.9% and 5.0% for Te(IV) and Te(VI), respectively, were obtained. The developed IL-CPE method was successfully applied for Te speciation analysis in matrices of different complexities, such as waters (tap, underground and seawater), soil and sediment.

A simple and efficient preconcentration method based on vortex assisted reduced graphene oxide magnetic nanoparticles for the sensitive determination of endocrine disrupting compounds in different water and baby food samples by GC-FID

This study utilized reduced graphene oxide magnetic nanoparticles Fe3O4/rGO-MNP to preconcentrate two alkyl phenols, two organochlorine pesticides and one organophosphate pesticide from water and baby food samples for the determination by gas chromatography flame ionization detector (GC-FID). Parameters of the micro-solid phase extraction (μ-SPE) were fully optimized to boost the measurement signals of the analytes. Optimum extraction conditions were applied to aqueous standard solutions to validate the method. The limit of detection ranged between 0.48 and 2.4 μg/L, recording about 60–100 folds enhancement in detection power when compared directly with the detection limits of the instrument before preconcentration. The optimum method was applied to aqueous samples and spiked recovery tests produced satisfactory results. The baby food sample was treated with the QuEChERS standard method before applying the μ-SPE method. Matrix matching was used to overcome matrix interference to obtain approximately 1.0 % recovery results for all analytes spiked at different concentrations.

Supercritical fluid extraction followed by supramolecular solvent microextraction as a fast and efficient preconcentration method for determination of polycyclic aromatic hydrocarbons in apple peels.

In this work, reverse micelle-based supramolecular solvent microextraction method coupled with supercritical fluid extraction and used for determining trace amounts of polycyclic aromatic hydrocarbons in apple peels. The extract was analyzed by high-performance liquid chromatography equipped with a fluorescence detector. Coupling supramolecular solvent microextraction with supercritical fluid extraction method, resolve low preconcentration factor of supercritical fluid extraction method, improved limit of detection of polycyclic aromatic hydrocarbons and allow the use of supramolecular solvent microextraction in solid matrices. The effective parameters on the supramolecular solvent microextraction and supercritical fluid extraction efficiency were optimized using one variable at a time and face centered design methods, respectively. Under the optimum condition, the limits of detection and limits of quantifications were in the range of 0.34-1.27 and 1.03-3.82µg/kg, respectively. Analysis of polycyclic aromatic hydrocarbons in apple peels showed that the supercritical fluid extraction/ supramolecular solvent microextraction method provide great potential for trace analysis of polycyclic aromatic hydrocarbons in fruit samples (RSDs<7.7%).

CO2-effervescence assisted dispersive micro solid-phase extraction based on a magnetic layered double hydroxide modified with polyaniline and a surfactant for efficient pre-concentration of heavy metals in cosmetic samples.

In this paper, a CO2-effervescence assisted dispersive micro solid-phase extraction procedure (CO2-EA-DμSPE) using a magnetic layered double hydroxide modified with polyaniline and a surfactant (Zn-Al-LDH-PA-DBSNa-Fe3O4) was applied for the pre-concentration of heavy metals (Ni2+, Pb2+, Co2+, and Cd2+). The final analysis of the analytes was carried out by atomic absorption spectroscopy. XRD, FTIR, and SEM studies were used for the characterization of the synthesized nanoadsorbent. For the maximum extraction efficiency, effective factors (including pH, nanoadsorbent dosage, and volume of the eluent) were investigated using the central composite design (CCD) method. Under the optimum conditions, the preconcentration factor was more than 20. The linear ranges for Ni2+, Pb2+, Co2+, and Cd2+ were obtained as (5-550), (7-750), (5-500), and (3-100) ng mL-1, respectively. The proposed method provided low detection limits (1.4, 2.1, 1.5, and 0.9 ng mL-1 for Ni2+, Pb2+, Co2+, and Cd2+, respectively) and suitable repeatability (relative standard deviation values (RSDs) below 6.1%, n = 6). Finally, the current method was successfully used for the extraction of heavy metals from cosmetic samples.

A highly efficient preconcentration route for rapid and sensitive detection of endotoxin based on an electrochemical biosensor.

An impedimetric aptasensor for the detection of endotoxin in a microfluidic chip was proposed, in which the Apt/AuNPs/SPCE sensing surface was fabricated in a screen-printed electrode with good biological activity and stability. The quantitative detection of endotoxin was accomplished by electrochemical impedance spectroscopy (EIS) measurement before and after exposing to samples. The impedance biosensor offers an ultrasensitive and selective detection of endotoxin down to 500 pg mL-1 with a wide linear range from 500 pg mL-1 to 200 ng mL-1. According to the Langmuir isotherm model, the interactions between the target molecules and the sensing surface had been analyzed and strong binding was concluded. Compared to the traditional static incubation methods, the microfluidic biosensor realizes the enrichment of endotoxin owing to the confined space and continuous flow nature, so that the lowest detection concentration is reduced from 5 ng mL-1 to 500 pg mL-1, which is much lower than the existing technology, and the total assay time is shortened from 1.0 h to 0.5 h. The proposed microfluidic impedance biosensor provides a new strategy for the design of an aptasensor to realize the rapid detection of target biomolecules with high sensitivity and it can be integrated into wearable medical devices due to its flexible properties.

Ultrasensitive SERS-Based Plasmonic Sensor with Analyte Enrichment System Produced by Direct Laser Writing.

We report an easy-to-implement device for surface-enhanced Raman scattering (SERS)-based detection of various analytes dissolved in water droplets at trace concentrations. The device combines an analyte-enrichment system and SERS-active sensor site, both produced via inexpensive and high-performance direct femtosecond (fs)-laser printing. Fabricated on a surface of water-repellent polytetrafluoroethylene substrate as an arrangement of micropillars, the analyte-enrichment system supports evaporating water droplet in the Cassie–Baxter superhydrophobic state, thus ensuring delivery of the dissolved analyte molecules towards the hydrophilic SERS-active site. The efficient pre-concentration of the analyte onto the sensor site based on densely arranged spiky plasmonic nanotextures results in its subsequent label-free identification by means of SERS spectroscopy. Using the proposed device, we demonstrate reliable SERS-based fingerprinting of various analytes, including common organic dyes and medical drugs at ppb concentrations. The proposed device is believed to find applications in various areas, including label-free environmental monitoring, medical diagnostics, and forensics.

Coupling Single-Drop Microextraction with SERS: A Demonstration Using p-MBA on Gold Nanohole Array Substrate.

Single-drop microextraction (SDME) was coupled with surface-enhanced Raman scattering (SERS) to provide sample extraction and pre-concentration for detection of analyte at low concentrations. A gold nanohole array substrate (AuNHAS), fabricated by interference lithography, was used as SERS substrate and para-mercaptobenzoic acid (p-MBA) was tested as a probe molecule, in the concentration range 10−8–10−4 mol L−1. With this approach, a limit of 10−7 mol L−1 was clearly detected. To improve the detection to lower p-MBA concentration, as 10−8 mol L−1, the SDME technique was applied. The p-MBA Raman signature was detected in two performed extractions and its new concentration was determined to be ~4.6 × 10−5 mol L−1. This work showed that coupling SDME with SERS allowed a rapid (5 min) and efficient pre-concentration (from 10−8 mol L−1 to 10−5 mol L−1), detection, and quantification of the analyte of interest, proving to be an interesting analytical tool for SERS applications.

Preconcentration of ultrafine ilmenite ore using a superconducting magnetic separator

The ilmenite lain in ultrafine ilmenite ore cannot be treated easily. In this study, a superconducting magnetic separator (SMS) was proposed to preconcentrate the ultrafine ilmenite. During this process, the essential condition for capturing the ilmenite from the ultrafine ore, key technology for obtaining an efficient preconcentration, and analysis of the ilmenite concentrates were investigated with theoretical descriptions, statistically designed experiments, and scanning electronic microscopy (SEM) detection, respectively. The descriptions and experiments indicated that the grade and recovery of ilmenite concentrate can be increased by the high-velocity slurry and high-intensity magnetic field, respectively; the synergy of the slurry velocity and magnetic intensity was demonstrated to be the key technology to improve the preconcentration efficiency. The SEM analysis demonstrated that the minimal agglomeration between ultrafine minerals in SMS further benefited the efficient preconcentration. Hence, the SMS provides an efficient way to preconcentrate ultrafine ilmenite ore.

Synthesis of sulphonic acid functionalized magnetic mesoporous silica for Cu(II) and Co(II) adsorption

Sulphonic acid functionalized core-shell magnetic mesoporous silica nanoparticles have been synthesized and used for preconcentration and enrichment of Cu(II) and Co(II). Mercapto groups were introduced via co-condensation which were then oxidized by H2O2 to incorporate the sulphonic acid functionality on the silica shell. The higher surface area of the sorbent and magnetic core simplified the extraction process. The adsorption of Cu(II) and Co(II) was achieved in less than 30 min at pH 7. The data showed that the adsorption mechanism followed pseudo-second order rate. The experimental data fits well in Langmuir, Freundlich and Temkin adsorption models. The maximum adsorption capacities for Cu(II) and Co(II) were 132 mg/g and 99.1 mg/g respectively. The newly synthesized material was successfully employed to develop an efficient preconcentarion method prior to the analysis of Cu(II) and Co(II) by graphite furnace atomic absorption spectrometer (GFAAS). The factors affecting the analysis were optimized and interferences from co-existing ions were also investigated. The detection limits for Cu(II) and Co(II) were 20 ng/L and 27 ng/L respectively. The results indicate that the new sorbent can be used for efficient preconcentration of Cu(II) and Co(II) from complex environmental samples.

Ultrasound assisted combined molecularly imprinted polymer for the selective micro-solid phase extraction and determination of aflatoxins in fish feed using liquid chromatography-tandem mass spectrometry

A combined procedure based on using ultrasounds for target isolation followed by porous membrane-protected micro solid phase extraction using a molecularly imprinted polymer as an adsorbent has been developed as a highly selective extraction and clean-up procedure for isolating aflatoxins B1, B2, G1, and G2 from fish feed before ultra-high-performance liquid chromatography tandem mass spectrometry determination. Polymeric adsorbent beads have been synthesized by the precipitation polymerization method which guarantees a homogeneous particles size distribution and the integrity of the generated imprinted cavities. In addition, polymerization was performed using a higher proportion of organic solvent (toluene) in the porogen mixture, which generates MIP particles adequate for interacting with targets dissolved in organic (hydro-organic) mixtures (extracts from fish feed). These approaches led to a selective and high efficient pre-concentration method for AFs. Ultrasound-assisted extraction (10 mL of 60:40 acetonitrile/0.1 M KH2PO4 pH 6.0, 40% amplitude, continuous sonication for 7.0 min) allowed an efficient aflatoxins isolation from fish feed. In addition, the resulting pH of the extract (pH 7.0) has been found to be the optimum for performing clean-up/pre-concentration (enrichment factor of 33.3) by molecularly imprinted polymer based micro-solid phase extraction (orbital horizontal shaking speed at 150 rpm for 10 min for loading, and 5 mL of 95:5 acetonitrile/formic acid as eluting solution using ultrasounds 35 kHz for 15 min). The current proposal was shown to be an accurate and precise method through relative standard deviation of intraday and inter-day tests below 20% and analytical recoveries in the range of 80–100%. The limits of detection were within the 0.42–1.15 μg kg−1 range, quite lower than those established by European Commission guidelines for aflatoxins in animal feeds.

Large‐volume sample stacking with polarity switching for analysis of azo dyes in water samples by capillary electrophoresis

ABSTRACTA simple, fast and efficient on-line pre-concentration method (large-volume sample stacking) by capillary electrophoresis was proposed for determination of azo dyes residues (allura red [AR], sunset yellow [SY] and tartrazine [TAR]) in water samples. Pre-concentration variables involved in the system were optimised using of a Box–Bhenken design. Under the optimal conditions: injection time 150.0 s, pre-concentration time 120.0 s and reverse potential −8.0 kV, the proposed methodology improved the analytical sensibility achieving limits of detection of 21.0–41.4 µg L−1 with enrichment factors of 82.1–210.8 fold. The large-volume sample stacking-capillary electrophoresis method was validated and applied to determine azo dyes residues in 20 water samples (bottled, spring and tap water). Two samples were positive for sunset yellow and tartrazine with a concentration of 25.3 and 30.2 µg L−1 and % RSD less than 10.0% in all cases.

Application of zinc/aluminum layered double hydroxide nanosorbent in a fixed-bed column for SPE-preconcentration followed by HPLC determination of diclofenac in biological and hospital wastewater samples

A zinc/aluminum layered double hydroxide (Zn/Al LDH) with carbonate interlayer anions was synthesized by the co-precipitation method. The prepared sorbent was examined for the solid phase extraction (SPE) and high performance liquid chromatography (HPLC) determination of the trace amounts of diclofenac (DCF) in human serum, as a complex matrix, and hospital wastewater samples. The first step of the procedure was the extraction of DCF by the synthesized Zn/Al LDH via an anion exchange mechanism, in which the interlayer carbonate anions were involved. A univariate sequential optimization procedure was conducted to find the optimal value of the parameters affecting the extraction process. The second step was the elution of the adsorbed DCF by a sodium hydroxide solution (2 mol L−1), followed by HPLC analysis of DCF. Under the optimal experimental conditions, the calibration plots for the determination of DCF in hospital wastewater and human serum samples were linear in the ranges of 3–415 (R2 = 0.999) and 9–300 (R2 = 0.997) μg L−1, respectively. The corresponding limits of detection were found to be as 0.16, 1.5 μg L−1, and the evaluated preconcentration factors were 41 and 37. The stability of the studied LDH allowed using a column packed with this adsorbent for 185 adsorption-desorption cycles. The results demonstrated the potentials of the developed method for efficient preconcentration and thus precise trace analysis of DCF in real samples.

Mineralogical and Chemical Characterization of Zr-REE-Nb Ores from Khalzan Buregtei (Mongolia)—Approaches to More Efficient Extraction of Rare Metals from Alkaline Granitoids

Alkaline rocks are worldwide observed as hosts for rare metal (Zr-REE-Nb) minerals. The classification of the ore bearing rock type is challenging due to the fact that textures and mineral assemblage are obscured by post-magmatic alteration. In addition, the alteration causes fine and intricate intergrowth of the ore minerals with associated gangue. Hence, intensive comminution is necessary to liberate the ore minerals, which is one parameter hampering the economical use of this deposit type. This study provides a quantitative mineralogical investigation of the ore bearing rock suite at Khalzan Buregtei as an example of rare metal deposits. R1-R2 multication parameters are shown to be highly appropriate as quantitative mineralogical indicators based on readily available major element datasets to visualize and quantify alteration types of the ore bearing rock suite. The ore minerals were found to be associated with a cluster-forming assemblage of post-magmatic phases. Automated mineralogy was applied to quantify the textural properties of the ore mineral clusters. This finding permits efficient pre-concentration of rare metal ore at coarser particle size fraction, requiring less energy consuming comminution.

Dispersive liquid–liquid microextraction based on green type solvents—"deep eutectic solvents"—for highly selective separation and efficient preconcentration of nickel in water samples

This study proposed a fast, feasible, and sensitive method for nickel preconcentration and separation in different actual samples through the use of deep eutectic solvent based dispersive liquid–liquid microextraction (DES-DLLME). This method involves dissolving a suitable extraction solvent in a dispersive solvent and its rapid syringing into water sample to obtain a turbid solution. Phase separation could be then carried out by centrifugation and the analyte can be determined. 2,2′-furildioxime was employed as the chelating agent through formation of a hydrophobic complex with nickel. To reach maximum recovery, some variables including type and volume of dispersive solvent, volume of extraction solvent, pH, 2,2′-furildioxime concentration, and salt concentration were optimized. Under optimal conditions, nickel calibration graph was linear in the range of 5.0–100 µg L−1. The detection limit and preconcentration factor were obtained as 1.7 µg L−1 and 40 µg L−1, respectively. Finally, this method was successfully applied for the extraction and determination of nickel in water samples with a relative recovery of 98.8–101.0%.