Magnetic solid-phase extraction using polydopamine-coated magnetic multiwalled carbon nanotube composites coupled with high performance liquid chromatography for the determination of chlorophenols

Magnetic multi-template molecularly imprinted polymers for selective simultaneous extraction of chlorophenols followed by determination using HPLC

Magnetic multi-template molecularly imprinted polymers (M-mt-MIPs) were successfully synthesized by surface imprinting and multi-template imprinting strategy, using polydopamine coated magnetic multi-walled carbon nanotubes as supporting materials, five typical chlorophenols (CPs) as templates, methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linker. Compared to non-imprinted polymers (NIPs), the as-prepared M-mt-MIPs showed high adsorption capacity (32.58‒80.63 mg g-1), rapid mass transfer and specific selectivity for the five targeted CPs, which were applied as magnetic solid-phase extraction (MSPE) adsorbents. Parameters affecting MSPE efficiency were detailed investigated, such as adsorbents dosage, sample pH, extraction time, type and volume of desorption solvent and salt effect. Combined with HPLC-DAD, a simple, rapid and sensitive method was established, showing good linearity (2‒200 μg L-1), low limits of detection (0.32‒0.49 μg L-1), and high enrichment factors (35.2‒108). The developed M-mt-MIPs-MSPE-HPLC method was applied to enrich and determine CPs in tannery wastewater, wet-blue and crust leather, and satisfactory spiking recoveries were attained in the range of 73.95‒109.7% with relative standard deviations (RSDs) of 2.13-8.48%. This study provided a new alternative material and method to rapid simultaneously extract and analyze low concentration of typical CPs in complicated matrices.

Harnessing an amide-based covalent organic framework in solid-phase extraction for chlorophenol analysis in industrial wastewaters

An amide-based covalent organic framework (COF) was successfully synthesized using the reaction between 1,3,5-trimesoyl chloride and ethylenediamine. The structure and morphology of the COF were characterized using Fourier-transform infrared spectra, nuclear magnetic resonance spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area analysis. The COF was employed as a solid-phase extraction adsorbent for the sampling and preconcentration of chlorophenols from industrial wastewater samples prior to high-performance liquid chromatography with ultraviolet detection. The experimental parameters influencing the extraction efficiency including type and volume of eluent solvent, sample solution volume, salt concentration, sample flow rate, and sample solution pH were investigated and optimized using a response surface methodology employing Box-Behnken-design. Under optimized conditions, calibration curves exhibited good linearities over the range of 0.003-10 µg/mL with determination coefficients (R2) ranging from 0.9982 to 0.9999. The method's limits of detection ranged from 0.001 to 0.01 µg/mL. Good repeatability was achieved with relative standard deviations below 4.7%. The developed procedure utilizing the COF adsorbent was successfully applied to determine chlorophenols accurately and precisely in various industrial wastewater samples.

Preparation of a magnetic phosphazene-based hyper crosslinked polymer for the fast and efficient extraction of chlorophenols from water and peach juice

Two magnetic phosphazene-based hyper crosslinked polymers (M-HCP-OP-TMC and M-HCP-OP-TCL) were newly synthesized by the reaction of Friedel-Crafts acylation, and the M-HCP-OP-TMC showed an excellent extraction capability and rapid adsorption kinetics for chlorophenols as an adsorbent. Then, an efficient analytical method was built for the preconcentration and quantification of chlorophenols from water and peach juice samples by combining M-HCP-OP-TMC based magnetic solid-phase extraction (MSPE) with HPLC-UV detection. The linear response range for the chlorophenols by the method was 0.21-100.0 ng mL-1 for water sample, and 0.36-100.0 ng mL-1 for peach juice sample. The detection limits (S/N = 3) of the proposed method for the analytes were 0.07- 0.25 ng mL-1 and 0.12-0.45 ng mL-1 for water and peach juice samples, respectively. The method recoveries for the spiked samples were in the range of 93.1%-117.1%, and the relative standard deviations were less than 10%. The adsorption of the chlorophenols with the M-HCP-OP-TMC was mainly contributed by π-π stacking and hydrophobic interactions. The results indicate that the method was sensitive and accurate enough for the determination of the chlorophenols from real samples.

Development of a Modified QuEChERS Method Based on Magnetic Multi-Walled Carbon Nanotubes as a Clean-Up Adsorbent for the Analysis of Heterocyclic Aromatic Amines in Braised Sauce Beef

Heterocyclic aromatic amines (HAAs) generated during the cooking of meats cause adverse effects on human health. The purpose of the current research was to develop a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method using magnetic multi-walled carbon nanotubes (Fe3O4-MWCNTs) as clean-up adsorbents for the rapid determination of HAAs in braised sauce beef. The significant parameters in extraction and clean-up processes were screened and optimized. Under optimal conditions, the LODs ranged from 3.0 ng/g to 4.2 ng/g. The recoveries (78.5−103.2%) and relative standard deviations RSDs (<4.6%) of five HAAs were obtained. These are in accordance with the validation criteria (recovery in the range of 70−120% with RSD less than 20%). Compared with conventional clean-up adsorbents (PSA or C18), Fe3O4-MWCNTs displayed equivalent or better matrix removal efficiency, while making the pretreatment process easier and more time-saving through magnetic separation. Less usage of adsorbent makes the method possess another advantage of being lower in cost per sample. The method developed was successfully applied to analyze real samples collected from local deli counters, demonstrating Fe3O4-MWCNTs could be considered as an effective alternative adsorbent with great potential in the QuEChERS process.

Synthesis of nitrogen-rich magnetic hypercrosslinked polymer as robust adsorbent for the detection of neonicotinoids in honey, tomatoes, lettuce and Chinese cabbage

In this study, a novel nitrogen-rich magnetic hypercrosslinked polymer (Fe3O4@Ph-HCP) was fabricated via a facile one-pot reaction of 1,3,5-triphenylbenzene, 2,4-dichloropyrimidine and phenyl-functionalized magnetic Fe3O4 nanoparticles. The Fe3O4@Ph-HCP possessed high specific surface, abundant nanopores and good stability. Especially, Fe3O4@Ph-HCP exhibited excellent adsorption capability with fast adsorption rate to neonicotinoid insecticides. It was applied as a superior magnetic adsorbent for rapid enrichment and isolation of four neonicotinoid insecticides (thiamethoxam, imidacloprid, acetamiprid and thiacloprid) from honey, tomato, lettuce and Chinese cabbage samples prior to high performance liquid chromatography-diode array detection. Under the optimized conditions, the good linearity was obtained in the range of 1-1000 ng g-1 for honey, tomato, lettuce and Chinese cabbage samples, and the detection limits (S/N = 3) were 0.30-0.67 ng g-1 for honey, 1-1.5 ng g-1 for tomato, lettuce and Chinese cabbage. The spiked recoveries were 80.1-111%, and relative standard deviations were less than 10.0%. These results demonstrate that the developed method can be used as a good alternative method for sensitive determination of neonicotinoid insecticides in complex samples.

Sugar based cationic magnetic core-shell silica nanoparticles for nucleic acid extraction

Nucleic acid (NA) extraction is an essential step in molecular testing for a wide range of applications. Conventional extraction protocols usually suffer from time consuming removal of non-nucleic acid impurities. In this study, a new magnetic nanoparticle (MNP) is presented to simplify the NA extraction. A core-shell design, comprising of a ferromagnetic core coated with mesoporous silica, forms the basis of the functional nanoparticle. Chemical functionalization of the silica coating includes a multistep synthesis, in which an activated nanoparticle is coupled with a triethylene glycol spaced glycosyl imidazole. The molecular design aims for charge interactions between the imidazolium-based positive nanoparticle surface and nucleic acids, with specific hydrogen bonding between the surface bonded carbohydrate and nucleic acid targets to ensure nucleic acid selectivity and avoid protein contamination. Two different carbohydrates, differing in molecular size, were selected to compare the efficiency in terms of NA extraction. A triethylene glycol spacer provides sufficient flexibility to remove particle surface constraints for the interaction. The Brunauer-Emmett-Teller (BET) analysis shows a significantly larger surface area for the disaccharide-based particles NpFeSiImMalt (∼181 m2 g-1) compared to the monosaccharide analogue NpFeSiImGlc (∼116 m2 g-1) at small particles sizes (range ∼ 15 nm) and sufficient magnetization (29 emu g-1) for easy isolation by an external magnetic field. The particles enabled a high DNA particle loading ratio of 30-45 wt% (MNP/DNA ratio), reflecting an efficient extraction process. A high desorption rate (7 min) with more than 86% of unchanged DNA loading was recorded, indicating low damage to the target extract.