[Zirconium-based metal-organic framework composites for solid phase extraction of brevetoxin-A from seawater].

Red tides are a type of natural marine disaster caused by harmful algae characterized by a high toxicity, wide distribution, and long duration. Since the concentration of algal toxins in seawater increases with the occurrence of red tides, algal toxins detected in seawater could be used to predict the occurrence and evolution of red tides. Brevetoxin-A (BTX-A) is a secondary metabolite produced by the harmful algae Karenia brevis, whose detection in seawater could form the basis of an accurate warning system for incoming red tides. However, due to the inherent complexity of the seawater matrix and the extremely low levels of BTX-A in seawater, the use of instruments for its direct detection is difficult. Therefore, there is an urgent need to develop a sample pretreatment method for the efficient enrichment of BTX-A in seawater. In this study, a metal-organic backbone material (UiO-66) and its composite with silica microspheres (SiO2@UiO-66) were successfully synthesized using the solvothermal method. The prepared SiO2@UiO-66 exhibited good hydrophilicity, water stability, and large specific surface area. Furthermore, it also exhibited hydrogen bonding and electrostatic interactions with BTX-A, had a strong affinity for BTX-A, and was able to efficiently adsorb BTX-A in complex matrices. Therefore, SiO2@UiO-66 showed potential as a novel packing material for the extraction of BTX-A from solid phase extraction columns. Combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), a highly sensitive detection method for the determination of BTX-A in marine water was established. The established analytical method had a low detection limit (3.0 pg/mL), a wide linear range (10.0 -200.0 pg/mL), and a good linear relationship (R=0.9992). Combined with the Fujian Province Red Tide Monitoring and Early Warning Information 2021 issued by the Fujian Provincial Oceanic and Fisheries Bureau, the analytical method established herein was successfully applied to analyze and monitor the content of BTX-A in actual seawater samples. This highlights the proposed system's potential for use as an early warning factor in the monitoring of red tides, representing a simple and fast pretreatment methodology for the detection of BTX-A in seawater.

Hollow zirconium-porphyrin-based metal-organic framework for efficient solid-phase microextraction of naphthols.

In this work, a hollow zirconium-porphyrin-based metal-organic framework (HZ-PMOF) was prepared as a coating for solid-phase microextraction (SPME) fiber to determine two naphthols. HZ-PMOF coating provided good extraction performance for naphthols because of the rich forces including π-π interactions, hydrogen bonding, and electrostatic interaction between the materials and targets. Furthermore, due to the special shape of the hollow structure, HZ-PMOF coating showed time-saving SPME equilibrium time and higher extraction capacity than zirconium-porphyrin-based metal-organic framework (Z-PMOF) coating without hollow structure. Combining with gas chromatography-tandem mass spectrometry (GC-MS/MS), an analytical method of naphthols with low detection limit (1.0 ng L-1), wider linear range (3.0-1000.0 ng L-1) and good reproducibility (RSD ≤8.6%) was established. Subsequently, naphthols in water samples from five cities in China were successfully detected by this developed method with satisfactory recoveries (81.1%-117.9%) and precision (RSDs, 3.2-9.6%). The results indicated that the prepared HZ-PMOF-coated fiber has good application prospects, and would broaden the application of materials with special morphology in the field of pretreatment.

[Research progress in application of metal-organic framework-derived materials to sample pretreatment].

Sample pretreatment technology plays a vital role throughout the analysis of complex samples. Sample pretreatment can not only increase the concentration of trace targets in the sample, but also effectively eliminate interference from the sample matrix in instrumental analysis. Adsorbent materials are a key component of sample pretreatment technology. Therefore, the development of efficient and stable new adsorbent materials has acquired significance in research on pretreatment technology. Porous materials are advantageous for use in diverse applications, such as in adsorbents, when they possess controllable nanostructures, a tailored pore surface chemistry, and abundant porosity, and are inexpensive. Particularly in recent years, porous materials derived from metal-organic frameworks (MOFs) feature excellent properties, such as diverse morphology and structure, adjustable pore size, high specific surface area, good thermal stability, and chemical resistance. MOF-derived materials, when used as adsorbents for sample pretreatment, offer the following advantages: (1) The porous materials derived from MOFs typically possess a larger specific surface area than other porous materials. This characteristic is beneficial to improve the extraction capacity and extraction efficiency via an increase in the contact area between the materials and targets; (2) The microscopic porous structure of MOF-derived materials can be easily tuned (by controlling the temperature and time during pyrolysis, gas atmosphere, and heating rate), which is conducive to improve the selectivity of sample pretreatment methods; (3) The metal active sites can be evenly distributed. Owing to the ordered distribution of metal ions in the precursor MOFs and a good periodic framework structure, the metal active sites of the derivatives formed can still maintain a corresponding distance. These metal active sites will not form agglomerates and affect the extraction performance; conversely, other porous materials often require extremely complicated processes to achieve a uniform distribution; (4) Heteroatoms such as nitrogen and sulfur can be easily doped on the framework of MOF-derived porous materials. This doping enables the materials to induce additional interactions such as hydrogen bonding and π-π stacking for adsorbing target analytes. The excellent properties of MOF-derived materials make them promising for use in sample pretreatment. Novel sample pretreatment methods that use MOF-derived materials are constantly being developed. However, the use of MOF-derived materials is limited by the complex preparation process and high production cost of MOF precursors, along with difficulties in mass production. Further, the precise design or functionalization of MOF-derived materials according to the characteristics of targets is a new direction with immense challenges as well as application potential. This review summarizes the application of MOF-derived materials in sample pretreatment methods, including dispersive solid phase extraction (dSPE), magnetic solid phase extraction (MSPE), solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), and dispersive micro solid phase extraction (DMSPE). The preparation methods, functional control, and enrichment efficiencies of various MOF-derived materials are also reviewed. Finally, the application prospects of MOF-derived materials in sample pretreatment are discussed to provide a clear outlook and reference for further related research.

A dual-mode nanoprobe for the determination of parathion methyl based on graphene quantum dots modified silver nanoparticles.

We developed a highly sensitive and selective method for double-signal analysis (fluorescence and ultraviolet-visible spectrophotometry) of organophosphorus pesticides (OPs), based on reversible quenching of graphene quantum dots (GQDs; fluorophores) with silver nanoparticles (AgNPs; absorbers). We used acetylcholinesterase to catalytically convert acetylthiocholine into thiocholine. In turn, by competitive binding to the AgNPs, the produced thiocholine displaces AgNPs from the GQDs and thus induces fluorescence recovery. However, OP analytes inhibit the activity of acetylcholinesterase and, in so doing, retain the silver-graphene nanoparticle complex and fluorescence quenching. The degree of quenching is proportional to the concentration of OPs; the detection limit is as low as 0.017 µg/L. The ultraviolet-visible absorption of GQDs/AgNPs at 390 nm decreases-because of AgNP aggregation that occurs after desorption from the GQDs-and the absorbance is linearly proportional to the OP concentration. Our system has good selectivity to substances that are commonly present in water and vegetables. We successfully applied our method to OP analysis in water, apple, and carrot samples.

Preparation of zwitterionic cysteine-modified silica microsphere capillary packed columns for the on-column enrichment and analysis of glycopeptides in human saliva.

In this work, for the first time, L-cysteine (L-Cys), a zwitterionic hydrophilic compound containing abundant amino and carboxyl was modified on silica microspheres for the fabrication of SiO2@L-Cys capillary packed column. Since the SiO2@L-Cys capillary packed column possessed great hydrophilicity brought by L-cysteine, they could be utilized to enrich glycopeptides with a low detection limit of 5 fmol µL-1 HRP digests as well as a good selectivity of the mixture of HRP and BSA digests up to a molar ratio of 1:50. The capillary packed column were further applied into the glycosylation analysis of human saliva and 69 glycopeptides were identified from 2 µL human saliva digests.

Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: Operation parameters, microbial diversity and nutrient recovery potential.

Photobioreactor is deemed to be one of limiting factors for the commercial application of wastewater treatment based on microalgae cultivation. In this study, a novel Flat-Plate Continuous Open Photobioreactor (FPCO-PBR) was developed to treat piggery biogas slurry. The operation parameters, microbial stability and nutrient recovery potential of FPCO-PBR were investigated. Results showed that the appropriate influent mode for FPCO-PBR was multi-point or spraying mode. The optimal hydraulic retention time and interval time for biomass harvesting of FPCO-PBR were both 2 d. Nitrogen and phosphorus recovery rate were 30 mg L-1 d-1 and 7 mg L-1 d-1 respectively under optimal operating parameters. Microbial diversity remained relatively stable in FPCO-PBR. Biomass production rate of FPCO-PBR was 0.47 g L-1 d-1 under optimal operating parameters. The revenue generated from biomass was estimated to be 15.06 $ kg-1, which means that treating one ton of wastewater can generate $ 7.08 in revenue.

Analysis of Perfluorinated Compounds in Environmental Water Using Decyl-perfluorinated Magnetic Mesoporous Microspheres as Magnetic Solid-Phase Extraction Materials and Microwave-Assisted Derivatization Followed by Gas Chromatography-mass Spectrometry.

In this work, a new method was developed for perfluorinated compounds (PFCs) analysis in water samples based on decyl-perfluorinated magnetic mesoporous nanocomposites microspheres-assisted extraction and microwave-assisted derivatization followed by gas chromatography-mass spectrometry analysis. The decyl-perfluorinated magnetic mesoporous nanocomposites have several advantages such as fast separation ability, good dispersibility in water sample and high selective preconcentration of PFCs. Various parameters, including eluting solvent and volume, the amounts of absorbents, extraction time and elution time, the microwave-assisted derivatization conditions were optimized. Validation studies showed that this method has good linearity (r2 > 0.9970), satisfactory precision (RSD < 7.8%) and high recovery (93-107%). The limits of detection were found to be 0.055-0.086 µg/L and the limits of quantification be 0.18-0.28 µg/L, respectively. The results indicated that the proposed method has advantages of convenience, good sensitivity and high efficiency. The method has been applied successfully to analyze perfluorinated organic acids in real water samples.

Novel electrochemical immunoassay for human IgG1 using metal sulfide quantum dot-doped bovine serum albumin microspheres on antibody-functionalized magnetic beads.

A new magneto-controlled electrochemical immunosensing system was developed for the sensitive detection of low-abundance protein (IgG1 used in this case) with a sandwich-type assay format on monoclonal mouse anti-human Fab-specific IgG1-functionalized magnetic bead. Metal sulfide (CdS) quantum dot-doped bovine serum albumin (QD-BSA) was synthesized and functionalized with monoclonal Fc-specific anti-human antibody. In the presence of IgG1, the immobilized antibody on magnetic bead was selective to capture the Fab region of the analyte, followed to be sandwiched by the conjugated antibody onto QD-BSA. The subsequent anodic stripping voltammetric analysis of cadmium ion, released by acid from quantum dot, was conducted at an in situ prepared mercury film electrode. Under optimal conditions, the voltammetric current increased with the increasing of target IgG1 within a dynamic working range from 10 pg mL-1 to 100 ng mL-1. The limit of detection of this immunosensor was evaluated to 3.4 pg mL-1 at 3sblank criterion. The precision, selectivity and method accuracy were acceptable. Analysis of human serum samples revealed good accordance with the results obtained by commercial enzyme-linked immunosorbent assay method. Importantly, this concept offers promise for cost-effective analysis of low-abundance cancer biomarkers without the need of natural enzymes.

Target-responsive aptamer release from manganese dioxide nanosheets for electrochemical sensing of cocaine with target recycling amplification.

A novel electrochemical sensing platform based on manganese dioxide (MnO2) nanosheets was developed for sensitive screening of target cocaine with the signal amplification. Ferrocene-labeled cocaine aptamers were initially immobilized onto MnO2 nanosheets-modified screen-printed carbon electrode because of π-stacking interaction between nucleobases and nanosheets. The immobilized ferrocene-aptamer activated the electrical contact with the electrode, thereby resulting in the sensor circuit to switch on. Upon target cocaine introduction, the analyte reacted with the aptamer and caused the dissociation of ferrocene-aptamer from the electrode, thus giving rise to the detection circuit to switch off. The released aptamer was cleaved by DNase I with target recycling. Under optimal conditions, the decreasing percentage of the electronic signal relative to background current increased with the increasing cocaine concentration in the dynamic range of 0.1-20nM, and the detection limit was 32pM. The reproducibility, selectivity and method accuracy were acceptable. Importantly, this concept offers promise for rapid, simple, and cost-effective analysis of cocaine biological samples without the needs of sample separation and multiple washing steps.

Analysis of chlorophenols in environmental water using polydopamine-coated magnetic graphene as an extraction material coupled with high-performance liquid chromatography.

In this work, polydopamine-coated magnetic graphene nanocomposites were synthesized by a simple solvothermal reaction and self-polymerization of dopamine, and the as-made nanocomposites were successfully applied as an effective adsorbent for the preconcentration of the four chlorophenols in environmental water samples before high-performance liquid chromatography. The polydopamine-coated magnetic graphene nanocomposites have several advantages such as a high surface area, fast separation ability, super-hydrophilicity, and high peak intensities for aromatic analytes. Various parameters, including eluting solvent and volume, the amounts of absorbents, extraction time and elution time were optimized. Validation experiments showed that the optimized method had good linearity (r(2) > 0.9990), satisfactory precision (RSD < 6.7%) and high recovery (90-105%). The limits of detection were 0.013-0.020 µg/L and the limits of quantification ranged from 0.043 to 0.070 µg/L. The results indicated that the proposed method had advantages of convenience, good sensitivity, and high efficiency. The method has been applied successfully to analyze chlorophenols in real water samples.

Simultaneous Determination of Five Alkaloid Compounds in a Drug Based on a Hydrophilic Monolithic Column by Capillary Electrochromatography.

A novel capillary electrochromatography (CEC) method was developed by using a hydrophilic monolithic column for the simultaneous determination of five alkaloids in a drug. The monolithic stationary phase was first prepared via in situ polymerization of acrylamide (AM), glycidyl methacrylate (GMA), N,N'-methylenebisacrylamide (MBA) and 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) in a ternary porogen solvent system consisting of cyclohexanol, dodecanol and toluene. The obtained monolithic stationary phase was subsequently modified by 0.1 mol/L ammonia water for opening epoxide groups of GMA. The separation performance and efficiency of the resulting monolithic column were investigated by the use of five compounds (thiourea, aniline, naphthylamine, diphenylamine and dimethyl acetamide) by CEC. The optimized monolithic column has obtained high column efficiencies with 74,000-121,000 theoretical plates/m. Finally, the prepared monolithic column was used to separate and determine five alkaloids (piperine, nuciferine, kukoline, berberine and tetrandrine) using CEC. Under the conditions of acetonitrile/10 mM phosphate buffer solution (65/35, v/v, pH 8.5) and 15 kV applied voltage, the baseline separation of five alkaloids was achieved. The proposed method has been successfully applied to the determination of berberine in a tablet sample. The percentage of recovery of spiked tablet samples ranged from 93.4 to 108.0% with relative standard deviations (RSDs) <9.20%.

A novel fluorescent reagent for recognition of triplex DNA with high specificity and selectivity.

A fluorescent agent (DMT) was screened for recognizing triplex DNA with a specific and selective characteristic, which was embedded into the triplex DNA structure. The triplex DNA was firstly formed by a complementary target sequence through two distinct and sequential events. The conditions including pH and hybridization time, fluorescent agent concentration and embedding time were optimized in the experiment. Under the optimum conditions, the fluorescence signal was enhanced up to 9-fold in comparison with the DMT embedding into the ssDNA, dsDNA and G-quadruplexes. Under the same fluorescence conditions, the changes of the fluorescence signal were also investigated by several kinds of base mismatched DNAs in the experiment. The results showed that our biosensor provided excellent discrimination efficiency toward the perfectly mismatched target DNA with no formation of triplex DNA. We preliminarily deduced the mechanism of the fluorescent reagent for recognizing triplex DNA with high specificity and selectivity.

Simultaneous determination of nucleoside and purine compounds in human urine based on a hydrophobic monolithic column using capillary electrochromatography.

A novel capillary electrochromatography method was developed by using a polymethacrylate ester based monolithic column for the simultaneous separation and determination of five nucleoside and purine compounds in urine. The porous monolithic column was first designed by mean of in situ copolymerizing stearyl methacrylate, trihydroxymethylpropyl trimethylacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid in a ternary porogenic solvent including cyclohexanol, 1,4-butanediol, and water. The performance and influence factors of the monolithic columns were investigated and evaluated by a CEC method. The five compounds including guanine, adenine, adenosine, cytidine, and N6 -methyladenosine were selected as analytes. Under the optimized condition of 6.0 mM phosphate buffer at pH 5.0 without ACN, five analytes were rapidly separated in 4 min with the high separation efficiency. The recoveries of spiked samples were ranged from 89.0 to 109.0% with RSDs less than 4.83%. Therefore, the proposed method could possibly provide for rapid separation and detection of the nucleoside and purine compounds in biomedicine sample.

On-line concentration and pressurized capillary electrochromatography analysis of five ß-agonists in human urine using a methacrylate monolithic column.

A pressurized capillary electrochromatography (pCEC) method combined with an online concentration was developed for the separation and determination of five ß2 -blockers (terbutaline, salbutamol, formoterol, procaterol and salmeterol) in human urine. A stearyl methacrylate-based monolithic column was prepared as the separation column. The various separation parameters including acetontrile concentration, applied voltage, pH and concentration of the running buffer were investigated. On-line concentration methods in combination of the chromatographic zone-sharpening effect and field-enhanced sample-stacking effect were utilized to improve detection sensitivity. The on-line concentration parameters including injection voltage, injection time, as well as sample matrix were systematically studied. Compared with the conventional sample injection, the on-line concentration technique appeared to improve the corresponding sensitivities 20∽50-fold. Furthermore, good precision was obtained with relative standard deviations (RSDs) for retention times within 1.09% and for peak areas less than 3.55% (n = 5). The established method was successfully applied to the determination of above-mentioned ß2 -agonists in urine samples. The recoveries of spiked urine samples were between 85.0 and 113.3% with RSDs less than 5.39%.

Preparation and evaluation of a hydrophilic poly(2-hydroxyethyl methacrylate-co-N,N'-methylene bisacrylamide) monolithic column for pressurized capillary electrochromatography.

A polar polymethacrylate-based monolithic column was introduced and evaluated as a hydrophilic interaction CEC stationary phase. The monolithic stationary phase was prepared by in situ copolymerization of a neutral monomer 2-hydroxyethyl methacrylate and a polar cross-linker N,N'-methylene bisacrylamide in a binary porogenic solvent consisting of dodecyl alcohol and toluene. The hydroxyl and amino groups at the surface of the monolithic stationary phase provided polar sites which were responsible for hydrophilic interactions. The composition and proportion of the polymerization mixture was investigated in detail. The mechanical stability and reproducibility of the obtained monolithic column preformed was satisfied. The effects of pH and organic solvent content on the EOF and the separation of amines, nucleosides, and narcotics on the optimized monolithic column were investigated. A typical hydrophilic interaction CEC was observed on the neutral polar stationary phase. The optimized monolithic column can obtain high-column efficiencies with 62,000-126,000 theoretical plates/m and the RSDs of column-to-column (n = 9), run-to-run (n = 5), and day-to-day (n = 3) reproducibility were less than 6.3%. The calibration curves of these five narcotics exhibited good linearity with R in the range of 0.9959-0.9970 and linear ranges of 1.0-200.0 µg/mL. The detection limits at S/N = 3 were between 0.2 and 1.2 µg/mL. The recoveries of the separation of narcotics on the column were in the range of 84.0-108.6%. The good mechanical stability, reproducibility, and quantitation capacity was suitable for pressure-assisted CEC applications.

Capillary electrochromatography of three ß2-agonists in human urine using a lauryl methacrylate-based monolithic column.

A new method of online concentration capillary electrochromatography using a lauryl methacrylate-based monolithic column was developed for determination of three ß(2)-agonists including salbutamol, procaterol, and formoterol. The separation parameters including acetonitrile concentration, running buffer pH, and concentration were evaluated. To improve the sensitivity, an online concentration method with combination of the chromatographic zone-sharpening effect and field-enhanced sample-stacking effect has been developed in which the concentration parameters including injection voltage, injection time, as well as sample matrix were systematically studied. Under the optimized conditions, baseline separation of three ß(2)-agonists was achieved within 4 min. When compared to the conventional sample injection, this online concentration technique increased their corresponding sensitivities up to 45-, 36-, and 320-fold, respectively. Furthermore, good repeatability was obtained with relative standard deviations (RSDs) for migration times within 0.84% and those for peak areas less than 6.35% (n = 5) in the experiment. The proposed method was successfully applied to the determination of above-mentioned ß(2)-agonists in urine sample. The recoveries of spiked urine samples were between 82.4% and 109.1% with RSDs less than 9.97%.

Analysis of plant hormones by microemulsion electrokinetic capillary chromatography coupled with on-line large volume sample stacking.

A novel method of microemulsion electrokinetic capillary chromatography (MEEKC) coupled with on-line large volume sample stacking was developed for the analysis of six plant hormones including indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, 1-naphthaleneacetic acid, abscisic acid and salicylic acid. Baseline separation of six plant hormones was achieved within 10 min by using the microemulsion background electrolyte containing a 97.2% (w/w) 10 mM borate buffer at pH 9.2, 1.0% (w/w) ethyl acetate as oil droplets, 0.6% (w/w) sodium dodecyl sulphate as surfactant and 1.2% (w/w) 1-butanol as cosurfactant. In addition, an on-line concentration method based on a large volume sample stacking technique and multiple wavelength detection was adopted for improving the detection sensitivity in order to determine trace level hormones in a real sample. The optimal method provided about 50-100 fold increase in detection sensitivity compared with a single MEEKC method, and the detection limits (S/N = 3) were between 0.005 and 0.02 µg mL(-1). The proposed method was simple, rapid and sensitive and could be applied to the determination of six plant hormones in spiked water samples, tobacco leaves and 1-naphthylacetic acid in leaf fertilizer. The recoveries ranged from 76.0% to 119.1%, and good reproducibilities were obtained with relative standard deviations (RSDs) less than 6.6%.

Electrochromatographic characterization of methacrylate ester-based monolith and capillary electrochromatography separation of flavonoids.

A porous polymethacrylate ester-based monolithic column for capillary electrochromatography (CEC) was designed by mean of in situ co-polymerizing lauryl methacrylate (LMA), ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in a ternary porogenic solvent including cyclohexanol, 1,4-butanediol and water. After investigating the influence factors of the CEC monolithic columns, four flavonoids (i.e., Rutin, Quercetin, Kaempferol, and Quercitrin) were separated and assayed to evaluate this monolithic column with CEC method. Under optimum conditions, the CEC method exhibited high separation efficiency, with rapid separation time of 3-4 min, for the four flavonoid samples using 10mM phosphate buffer containing 70% acetonitrile (pH 9.0). Importantly, the proposed method could provide a promising approach for rapid separation and detection in biomedicine.

pCEC coupling with ESI-MS for the analysis of beta(2)-agonists and narcotics using a poly-(1-hexadecene-co-TMPTMA) monolithic column.

A pressure-assisted CEC with ESI-MS based on poly(1-hexadecene-co-trimethylolpropane trimethacrylate) monolithic column for rapid analysis of two beta(2)-agonists and three narcotics was established in this article. After the organic polymer-based monolithic column was prepared by an in-situ polymerization procedure, a systematic investigation of the pressure-assisted CEC separation and ESI-MS detection parameters was performed. Baseline separation of the studied analytes could be obtained using the solution containing 75% ACN v/v and 20 mmol/L ammonium acetate with pH 8.0 as running buffer, when applying separation voltage of 20 kV and assisted pressure of 5 bar. Under the optimized conditions, two beta(2)-agonists and three narcotics could be completely resolved and accurately determined within 15 min. Finally, the proposed method was successfully used for real urine samples detection.