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Chinese Journal of Chromatography
2022, Vol. 40, No. 10
Online: 08 October 2022

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Preface

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New developments in sample preparation and relevant techniques HUANG Xiaojia 2022, 40 (10):  861-861.  DOI: 10.3724/SP.J.1123.2022.08027 Abstract ( 48 )   HTML ( 41 )   PDF (490KB) ( 39 )

Reviews

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Application of smart responsive materials in phosphopeptide and glycopeptide enrichment ZHAO Yanqing, XU Wenhui, JIA Qiong 2022, 40 (10):  862-871.  DOI: 10.3724/SP.J.1123.2022.06026 Abstract ( 183 )   HTML ( 30 )   PDF (1555KB) ( 257 )   Phosphorylation and glycosylation of proteins, two of the most widely studied post-translational modifications (PTMs), have shown increasing potential in the early non-invasive diagnosis, prognosis, and therapeutic evaluation of diseases. Besides regulating the function of cell membranes and intracellular signal transduction, protein phosphorylation participates in mitochondrial function and cellular and transcriptional metabolism. Protein glycosylation plays an important role in both intracellular and extracellular signal transduction and intracellular endocytosis. Aberrant phosphorylation and glycosylation of proteins are frequently observed in clinical proteomic studies and in the discovery of disease-related biomarkers. There are generally three methods for detecting protein phosphorylation/glycosylation: isotope radiolabeling, western blotting, and mass spectrometry. Mass spectrometry has become the most important and advantageous detection method due to its high throughput and time- and labor-efficiency. However, phosphopeptides and glycopeptides have low stoichiometry and ionization efficiency, and a large number of non-phosphopeptides and -glycopeptides interference. These issues make it difficult to directly detect phosphopeptides and glycopeptides by mass spectrometry. Therefore, the enrichment of phosphopeptides and glycopeptides before mass spectrometry detection is a key step. At present, a variety of materials have been developed for enrichment studies of phosphopeptides and glycopeptides. For example, immobilized metal affinity (IMAC) and metal oxide affinity chromatography (MOAC) methods are mostly used for the enrichment of phosphopeptides. The IMAC mainly uses positively charged metal ions and negatively charged phosphate groups to attract each other for the purpose of enriching phosphopeptides. MOAC materials rely on the chelation of metal atoms and phosphate oxygens to capture phosphopeptides. IMAC and MOAC materials rely on strong interactions between metals and phosphate groups, which often lead to difficult elution. The enrichment method for glycopeptides is mainly based on the difference in hydrophilicity between glycopeptides and non-glycopeptides, which are mainly enriched by hydrophilic interaction chromatography (HILIC). In addition, materials containing compounds such as boronic acid and lectin materials are also widely used for the separation and enrichment of glycopeptides. Smart responsive materials have also been successively reported for the enrichment of phosphopeptides and glycopeptides due to their unique responsiveness and reversibility. Smart responsive materials can respond to external stimuli; undergo structural and property changes; and convert signals such as optical, electrical, thermal, and mechanical into biochemical signals. Responsive molecules are a prerequisite for determining the response properties of smart responsive materials, and their reversible isomerization under different stimuli (such as temperature, pH, light, mechanical stress, and electromagnetic field) will lead to dynamic changes in the physical and chemical properties of materials. Compared with traditional materials, smart responsive materials can be reversibly “turned on” and “off” with better controllability. Exogenous stimuli, including temperature, light, ultrasound, electromagnetic field, and mechanical stress, can be implemented in a specific time and space. Exogenous responsive materials do not depend on changes in the reaction system itself and are non-invasive. Enzymes, pH, redox, solution polarity, and ionic strength are endogenous stimuli. Endogenous responsive materials depend on changes in the reaction system itself, and sometimes the regulation process requires the introduction of other chemicals into the reaction system. The identification, capture, and release of phosphopeptides or glycopeptides can be achieved by modulating the interactions between smart responsive materials and phosphopeptides or glycopeptides (such as hydrogen bonds, and electrostatic and hydrophobic interactions). This review classifies smart responsive materials according to the types of stimuli, which are specifically divided into exogenous and endogenous responsive materials. The enrichment of phosphopeptides and glycopeptides of exogenous/endogenous responsive materials and endogenous/exogenous co-responsive materials are summarized. In addition, we discuss the development prospects of smart responsive materials in the enrichment of phosphopeptides and glycopeptides, and also raised the challenges existing in the application of smart responsive materials in other protein post-translational modifications.

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Progress in sample pretreatment and detection methods of hexabromocyclododecanes CHENG Jiawen, MA Jiping, LI Shuang, TIAN Yong 2022, 40 (10):  872-881.  DOI: 10.3724/SP.J.1123.2022.03030 Abstract ( 207 )   HTML ( 32 )   PDF (1797KB) ( 92 )   Hexabromocyclododecanes (HBCDs) are a group of brominated flame retardants that are extensively employed in the industrial production of plastics, furniture, and construction materials. Due to their regular use and massive emissions, HBCDs have been distributed in the environment (air, water, soil, and sediments). Due to their high toxicity, persistent and long-distance transport, and bioaccumulation, HBCDs were listed in the Stockholm Convention in 2013. Thus, the accurate analysis and strict control of the pollution levels of HBCDs in environmental samples are critical to the government’s long-term environmental supervision mechanism. However, the concentration levels of HBCDs in real samples are low, combined with complex matrices, which seriously limits the determination of HBCDs. The target isomers are particularly transformed or degraded, which makes analysis challenging due to the high temperatures and specific organic solvents. The physicochemical features, toxic and environmental dangers, usage, and standard limitations of HBCDs are briefly discussed herein. Sample pretreatment and instrument detection of HBCDs in various matrices are summarized (i. e., soil, sediment, food, electronics, atmosphere, animals, and water). More than 70 research papers (2000-2022) from the Science Citation Index (SCI) and Chinese core publications are cited herein. First, the entire process of extraction, purification, separation, and enrichment of HBCDs is compared, including soxhlet extraction (SE), ultrasonic-assisted extraction (UAE), accelerated solvent extraction(ASE), supercritical fluid extraction (SFE), solid phase extraction (SPE), dispersed solid phase extraction (DSPE), liquid-liquid extraction (LLE), dispersive liquid-liquid microextraction (DLLME), and solid phase microextraction (SPME). In the literature, UAE is the most commonly employed process, accounting for a quarter of all HBCDs sample pretreatments. Additionally, SPE sample pretreatment technology can completely separate the targets and impurities to reduce the effect of matrix; and enrich the targets to improve sensitivity of method. By using SPE technology, the enrichment factor can be increased due to the massive sample volume, thus enabling detect HBCDs concentrations (nanogram per liter level) in water. Second, the advantages and disadvantages of instrument approaches are examined and discussed, including gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), liquid chromatography (LC), and liquid chromatography-tandem mass spectrometry (LC-MS/MS), which offer a reference for meeting the requirements in the determination of HBCDs in real samples, i. e., the total HBCDs can be detected by GC or GC-MS and three HBCD isomers (α-HBCD, β-HBCD, γ-HBCD) can be determined by LC or LC-MS. By using the triple quadrupole mass spectrometer, the sensitivity of the method can be improved. Till date, LC-MS/MS has been chosen as an instrument for the determination of HBCDs in various matrices (i. e., seawater, marine sediment, marine organisms, toys, and electronic products) in China. However, there are several challenges. The sample pretreatment is tedious; large sample volumes and organic solvent utilization. These challenges point to the development trends of analytical approaches for HBCDs. The development of green, automated, low-cost, fast, and efficient sample pretreatment approaches for new adsorption materials is the main development direction in the analysis of HBCDs in the future.

Mini-review

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Research progress on the application of derived porous carbon materials in solid-phase microextraction KUANG Yixin, ZHOU Suxin, HU Yalan, ZHENG Juan, OUYANG Gangfeng 2022, 40 (10):  882-888.  DOI: 10.3724/SP.J.1123.2022.06011 Abstract ( 173 )   HTML ( 39 )   PDF (1746KB) ( 78 )   The concentrations of target analytes in samples are low, and complex matrices can lead to a variety of interferences. Therefore, it is important to pretreat the samples before analysis. Compared to the time-consuming, tedious, and environmentally unfriendly solvent-based sample pretreatment methods, pretreatment techniques based on adsorption have more promising applications. Adsorption-based pretreatment technologies include solid-phase extraction, dispersive solid-phase extraction, magnetic solid-phase extraction, and solid-phase microextraction. Among them, solid-phase microextraction integrates sampling, extraction, enrichment, and injection into a single step. It has the advantages of being solvent-free, highly efficient, time efficient, and labor efficient. The extraction efficiency of solid-phase microextraction is closely related to the coating materials. There are various types of coating materials, including metal-organic frameworks, covalent organic frameworks, molecular imprinted polymers, porous carbon materials and so on. Porous carbon materials include traditional porous carbon materials such as activated carbon, carbon nanotubes, carbon molecular sieves, and derived porous carbon materials. Given their advantages of large specific surface area, controllable porous structure, large number of active sites, as well as good physical and chemical stability, porous carbon materials have been widely used in batteries, supercapacitors, catalysis, adsorption, and separation. Porous carbon materials are also popular coating materials for solid-phase microextraction. In particular, derived porous carbon materials find widespread use given their variety and designability. Most of these materials are derived from biomass and metal-organic framework precursors. In addition, past studies have mainly focused on the structural optimization of derived porous carbon materials. However, the applications of derived porous carbon materials in solid-phase microextraction are restricted by the following problems. (1) The preparation of porous carbon materials derived from covalent organic frameworks has seen great progress. However, there are only a few studies on their applications in solid-phase microextraction. (2) The prepared-derived porous carbon materials have excellent extraction abilities as when applied to solid-phase microextraction coatings. However, there is less systematic and clear mechanism to explain it. (3) Most derived porous carbon materials when used as solid-phase microextraction coatings show nice extraction performance only for specific analytes such as polar or non-polar substances. Therefore, in this paper, the research progress of derived porous carbon materials in solid-phase microextraction over the past three years has been summarized, and future research prospects have been prospected. Covalent organic frameworks can be used as precursors to prepare derived porous carbon materials with a narrow pore size distribution and a large specific surface area. It is necessary to further develop porous carbon materials derived from covalent organic frameworks as solid-phase microextraction coatings. The specific mechanism underlying this extraction effect should also be clarified. In addition, it is necessary to develop high-performance derived porous coating materials for broad-spectrum and high-sensitivity analysis of pollutants with different physical and chemical properties. Therefore, hierarchical porous carbon materials should be widely studied in solid-phase microextraction because of their multimodal pore sizes. A total of 56 references are cited in this paper, most of which are from the Elsevier database.

Articles

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Preparation and application of graphene oxide functionalized melamine-formaldehyde aerogel coated solid-phase microextraction tube SUN Min, LI Chunying, SUN Mingxia, FENG Yang, FENG Jiaqing, SUN Haili, FENG Juanjuan 2022, 40 (10):  889-899.  DOI: 10.3724/SP.J.1123.2021.12032 Abstract ( 131 )   HTML ( 18 )   PDF (2808KB) ( 50 )   Many solid-phase microextraction (SPME) sorbents have been developed from aerogels because of their low densities, large surface areas, and high porosities. Melamine-formaldehyde (MF) aerogel, made from melamine and formaldehyde by a sol-gel reaction, is one of the typical organic aerogels. MF aerogel has better mechanical strength, chemical stability and extraction performance than inorganic aerogels. The performance of the aerogel is limited in some fields, while composite aerogels can meet different requirements such as good mechanical strength and strong adsorption performance. Graphene oxide (GO) is a two-dimensional nanomaterial composed of a single layer of carbon atoms and provides π-π interaction by a large π-electron. In addition, the oxygen-containing groups at the edge of the lamellar structure improve the hydrophilicity of the material and can interact with various compounds. To improve the extraction performance of MF aerogel for polycyclic aromatic hydrocarbons (PAHs), GO/MF aerogels were prepared by functionalizing MF aerogel with GO. In this study, 1.2612 g of melamine and 80 mg of sodium carbonate were dissolved in 30 mL of water, and the mixture was heated to 80 ℃ under stirring. Then, 2.8 mL formaldehyde solution (37%) was slowly added, and a clear solution was obtained gradually. Next, 50 mg of GO powder was ultrasonically dispersed in 10.0 mL of water and evenly mixed with the above solution. After adjusting the pH to 1.5, the sol-gel process was performed for 48 h, then the gel was aged at room temperature for 24 h. The gel was then soaked in ethanol, acetone, and cyclohexane in turn to replace the solvent. Finally, the GO/MF aerogel was obtained by freeze-drying for 24 h. The GO/MF aerogel was characterized by scanning electron microscopy (SEM) and X-ray photoelectric spectroscopy (XPS), confirming that GO was successfully introduced into MF aerogel, while retaining its three-dimensional network and porous structure. GO/MF aerogel was coated onto the surface of a stainless steel wire to be used as sorbent. Four such wires were placed into a polyetheretherketone (PEEK) tube (0.75 mm i. d., 30 cm length) for in-tube (IT) SPME. The tube was combined with a high-performance liquid chromatography (HPLC) unit to construct an IT-SPME-HPLC online system. When the six-way valve was in the Load state, sample solution achieved online enrichment with analytes while it flowed through the extraction tube. After extraction, the valve was turned to the Inject state, and the analytes were eluted into the chromatographic column by the mobile phase at a flow rate of 1.0 mL/min for separation and detection with the detector. Under the same extraction conditions (sampling volume=30 mL, sampling rate=1.00 mL/min, and concentration of polycyclic aromatic hydrocarbons (PAHs, viz. naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorine (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla) and pyrene (Pyr))=5.00 μg/L), GO/MF aerogel-based tube was compared with that of MF aerogel-based tube. GO enhanced the enrichment efficiency of MF aerogel towards PAHs from 1.1 to 2.5 times, due to the increased number of adsorption sites and enhanced π-π interaction with PAHs. IT-SPME was affected by the sampling volume, sampling rate, concentration of organic solvent in sample, desorption solvent, desorption rate, and desorption time. To obtain accurate results, the main extraction and desorption conditions (sampling volume, sampling rate, organic solvent concentration, desorption time) were investigated carefully. As the sampling volume in the extraction tube was increased, the extraction efficiency was found to increase gradually until saturation. In this study, the extraction efficiency was investigated for sampling volumes ranging from 30 to 80 mL, and 70 mL was selected as a suitable sampling volume to achieve satisfactory extraction efficiency. The sampling rate affects not only the extraction efficiency, but also the extraction time. When the sample flows through the extraction tube at a low rate, it requires a long test time. Although the increase in sampling rate reduces the extraction time, it often decreases extraction efficiency. In addition, large sampling rate leads to high pressure in the tube, which in turn reduces the service life of the tube. Therefore, the effect of sampling rate (1.25-2.50 mL/min) on extraction efficiency was investigated, and good extraction efficiency and short test time were achieved when the sampling rate was 2 mL/min. High hydrophobic PAHs have poor solubility in water. An appropriate amount of organic solvent in the sample solution can improve the solubility of PAHs to obtain accurate analytical results. However, the extraction efficiency was affected by the added organic solvent. Thus, the effect of volume fraction of methanol (0, 0.5%, 1%, 2%, 3%, and 5%, v/v) on the extraction efficiency was investigated. The sample solution without methanol afforded better extraction efficiency and satisfactory repeatability. After online extraction, the desorption directly affects the desorption efficiency. The peak areas of the eight PAHs were investigated with different desorption times (0.2, 0.4, 0.6, 0.8, 1.0, and 2.0 min), and a desorption time of 2.0 min was required to fully desorb all analytes and reduce their residuals. The IT-SPME-HPLC-DAD method was established under the optimized conditions, and the limits of detection (LODs), linear equations, linear ranges, and correlation coefficients were obtained. The LODs of the eight PAHs were in the range of 0.001-0.005 μg/L, the quantitative ranges of the analytes were 0.003-15.0 μg/L for Fla and Pyr, 0.010-20.0 μg/L for Phe and Ant, and 0.017-20.0 μg/L for Nap, Acy, Ace and Flu, the enrichment factors were in the range of 2029-2875, and the analytical precision was satisfactory (intra-day RSD%≤4.8%, and inter-day RSD≤8.6%). Compared with some reported methods, the method reported herein provided higher sensitivity, wider linear range, and shorter test time. This method was applied to the detection of PAHs in common drinking water, including bottled mineral water and water from drinking fountain. The satisfactory recovery (76.3%-132.8%) obtained proves that the method is suitable for the determination of trace PAHs in real water samples, with high sensitivity, rapid testing, online detection, and good accuracy. The extraction tube also exhibited satisfactory durability and chemical stability.

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“One-pot” preparation of aminated carbon nanotube-modified magnetic nanoparticles and their application to the quantification of phenoxyacetic acid herbicides in cereal and vegetable samples HUANG Youfang, LIU Jun, HUANG Xiaojia 2022, 40 (10):  900-909.  DOI: 10.3724/SP.J.1123.2021.12008 Abstract ( 123 )   HTML ( 19 )   PDF (3357KB) ( 59 )   Phenoxyacetic acid herbicides (PAs) are widely used to control the growth of broad-leaf weeds in corn, tobacco, etc. The presence of PAs in plants even at low concentrations (at the ng/L to μg/L scale) may induce severe effects and lead to human health risks. Hence, a sensitive and reliable method for the determination of PAs at trace levels in cereals and vegetables is highly desired. Magnetic solid-phase extraction (MSPE) has attracted considerable attention on account of its benefits such as ease of separation, less solvent consumption, and good service life. In this study, aminated carbon nanotube-modified magnetic nanoparticles (NH2-CNTs@M) were prepared by a convenient and simple “one-pot” strategy and employed as the adsorbent for the MSPE of PAs in crops. The fabrication procedure is very convenient. In detail, the aminated carbon nanotubes, Fe(Ⅱ), Fe(Ⅲ), and isopropanol were mixed in one pot with mechanical stirring and reacted for 2.0 h at 80 ℃. The spectroscopic properties, morphology, and magnetic properties of the synthetic adsorbent were characterized by Fourier Transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed that the size of Fe3O4, diameter of NH2-CNTs, and the magnetic saturation values of NH2-CNTs@M were 30 nm, 40 nm, and 44.2 emu/g, respectively. Additionally, the results of FT-IR and TEM characterization confirmed the successful fabrication of NH2-CNTs@M by this “one-pot” hydrothermal approach. The NH2-CNTs@M displayed satisfactory capability to capture PAs through π-π, hydrophobic, and hydrogen-bonding interactions. To realize the best extraction performance, the key parameters, including the amount of adsorbent, formic acid concentration in the eluent, adsorption and desorption time, sample pH, and ionic strength in the sample matrices, were inspected and studied in detail. The optimal conditions were as follows: amount of NH2-CNTs@M, 30 mg; desorption solvent, 0.5 mL acetonitrile containing 2.0% (v/v) formic acid; adsorption and desorption times, 8.0 and 3.0 min, respectively; the sample pH was adjusted to 6.0, and no salt was added to the sample. Under the optimized extraction conditions, a sensitive, quick, and environmentally friendly method for the determination of the studied PAs in cereal and vegetable samples was established by the combination of NH2-CNTs@M/MSPE with high performance liquid chromatography-diode array detection (HPLC-DAD). The enrichment factors for the studied PAs varied from 73 to 90. The limits of detection (S/N=3) for the PAs in the cereal and vegetable matrixes were in the ranges of 0.32-1.6 μg/kg and 0.53-1.6 μg/kg, respectively; and the limits of quantification (S/N=10) for the PAs in the cereal and vegetable matrixes were 0.94-4.8 μg/kg and 1.6-4.8 μg/kg. The developed method also showed wide linear ranges and good precision. Finally, the established NH2-CNTs@M/MSPE-HPLC-DAD approach was applied to measure trace levels of PAs in cereals and vegetables, and good fortified recoveries (72.3% to 113%) and repeatability (RSDs below 10%) were obtained. The established approach has several advantages over the existing methods, such as high analytical speed, low LODs, and eco-friendliness.

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Efficient enrichment of pesticides from environmental water samples by cobalt-nickel double metal hydroxide nanocage/multiwalled carbon nanotube composites WANG Xuemei, YANG Jing, ZHAO Jiali, ZHOU Zheng, DU Xinzhen, LU Xiaoquan 2022, 40 (10):  910-920.  DOI: 10.3724/SP.J.1123.2022.03011 Abstract ( 120 )   HTML ( 24 )   PDF (7143KB) ( 52 )   Pesticides are widely used in agriculture to increase grain yields and prevent crop diseases and insect pests. However, pesticides pose a serious threat to ecosystems and human health owing to their high toxicity and persistence. Therefore, it is imperative to establish an efficient and sensitive detection method for pesticides in water samples. Rapid and accurate detection of trace pesticides in environmental water samples has been a challenge because of complex matrix effects and trace concentrations. Appropriate sample pretreatment is a critical step for the effective extraction of analytes and removal of interferences, and the development and design of novel and stable nanomaterial adsorbents is key to continuous innovation in sample pretreatment technology. In recent years, carboxylated multiwalled carbon nanotubes (MWCNTs-COOH) and layered double hydroxide (LDHs) have been widely used as new adsorbent materials for various pretreatment technologies because of their large specific surface area, good stability, and easy functionalization. Based on this background, MWCNTs-COOH and LDHs were combined to obtain a new efficient composite adsorbent, so that the synergistic effect of the individual components could be exploited in entirety. In this study, a zeolitic metal organic framework ZIF-67/multiwalled carbon nanotube (ZIF-67/MWCNTs) composite was prepared by a simple one-step method, and a cobalt-nickel double metal hydroxide/multiwalled carbon nanotube (CoNi-LDH/MWCNTs) hybrid material with a three-dimensional cage-like structure was synthesized by a solvothermal method using ZIF-67/MWCNTs as templates. The cage-like structure of the CoNi-LDH/MWCNTs composite, which is different from the traditional layered bimetallic hydroxide, could accelerate mass transfer. Given the excellent properties of the CoNi-LDH/MWCNTs composite, it was used as a solid-phase microextraction (SPME) coating for the efficient enrichment of six pesticides (chlorothalonil, tebuconazole, chlorpyrifos, butralin, deltamethrin, and pyridaben) and combined with high performance liquid chromatography-ultraviolet (HPLC-UV) detection for the determination of the six pesticides in real water samples. The prepared materials were characterized by scanning electron microscopy, electron dispersion spectroscopy, infrared spectroscopy, X-ray powder diffraction, and N2 adsorption/desorption. The results confirmed that the CoNi-LDH/MWCNTs composite was successfully synthesized, and that its surface area and pore volume were 281.4 m2/g and 0.49 cm3/g, respectively. An orthogonal array design was used to optimize the extraction conditions of SPME, including the extraction time, extraction temperature, stirring rate, salt effect, and desorption time. The optimal extraction conditions were as follows: extraction temperature, 40 ℃; extraction time, 30 min; stirring rate, 500 r/min; desorption time, 6 min; and salt (NaCl) mass concentration, 150 mg/L. Under optimal conditions, the method had a wide linear range (chlorothalonil: 0.015-200 μg/L, tebuconazole: 0.140-200 μg/L, chlorpyrifos: 0.250-200 μg/L, butralin: 0.077-200 μg/L, deltamethrin: 1.445-200 μg/L, pyridaben: 0.964-200 μg/L), low detection limit (0.004-0.434 μg/L), and good reproducibility. The relative standard deviations (RSDs) of single fiber and fiber-to-fiber were in the range of 0.5% to 5.7% and 0.5% to 4.8%, respectively. The spiked recoveries at two levels of 10.0 μg/L and 50.0 μg/L were in the range of 83.9%-108.2%, with RSDs less than 5.3%. Compared with other coated fibers (MWCNTs-COOH, ZIF-67, ZIF-67/MWCNTs, and silicone sealant), the CoNi-LDH/MWCNTs-coated fibers showed a better enrichment effect for pesticides, which was attributed to their high specific surface area and π-π interactions, hydrophobic interactions, cation-π interactions, and hydrogen bonding interactions between the CoNi-LDH/MWCNTs coating and the target analytes, which can enhance their ability to extract pesticides. The stability test on the SPME fibers revealed that after 128 cycles, the extraction efficiency of the CoNi-LDH/MWCNTs-coated fibers for the six pesticides decreased only slightly (< 10%), implying that the coated fibers had good stability and reusability. Therefore, this method can be used to detect pesticide residues in environmental water samples with high selectivity, sensitivity, and accuracy.

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Preparation of sulfonic acid-functionalized polymeric ionic liquid-based magnetic adsorbent and its applications to diquat extraction GUO Bingzhi, YANG Zhen, SUN Yaming, HE Lijun 2022, 40 (10):  921-928.  DOI: 10.3724/SP.J.1123.2022.01027 Abstract ( 133 )   HTML ( 11 )   PDF (2596KB) ( 113 )   In terms of the structure of polar pollutants, the design and development of new materials that can interact with target analytes is vital for effective extraction. Diquat is a broad-spectrum herbicide with strong toxicity. It is sprayed during the growing process of vegetables because of its high efficiency and low cost. Furthermore, diquat is a polar and basic cationic organic compound. Therefore, it is necessary to develop adsorbents that can form strong interaction with diquat to extract it from complex vegetable samples. In this study, sulfonic acid-functionalized ionic liquid, 1-vinyl-3-propyl(3'-sulfonate) imidazolium chloride ([VPImi-SO3H][Cl]), was synthesized through the reaction of 1-vinylimidazole and 1,3-propanesultone and characterized using nuclear magnetic-resonance spectroscopy. The resulting [VPImi-SO3H][Cl] was then immobilized on the surface of vinyl-modified magnetic silica to obtain poly-(1-vinyl-3-propyl(3'-sulfonate) imidazolium chloride)-modified magnetic nanoparticles (Poly([VPImi-SO3H][Cl])-MP) via free radical polymerization between vinyl groups. The structure, morphology and magnetism of the obtained Poly([VPImi-SO3H][Cl])-MP were characterized using Fourier transform infrared spectroscopy, scanning electron microscope, vibrating sample magnetometer, and thermogravimetric analysis. The characterization results indicated that the Poly([VPImi-SO3H][Cl])-MP was synthesized with strong magnetic properties. Poly([VPImi-SO3H][Cl])-MP as magnetic adsorbent exhibited a different pH response to anion and cation. With the increase in solution pH, the adsorption efficiency of Poly([VPImi-SO3H][Cl])-MP for anionic dye amaranth decreased; whereas, the adsorption efficiency for cationic dye, methylene blue, increased. Under a high pH condition, sulfonic acid groups on the surface of Poly([VPImi-SO3H][Cl])-MP existed in the form of -SO3-. Thus, the adsorption efficiency of Poly([VPImi-SO3H][Cl])-MP for methylene blue could reach 95.2% due to the strong electrostatic attraction between adsorbent and positively charged methylene blue; whereas, negatively charged amaranth could hardly be adsorbed due to the electrostatic repulsion between adsorbent and amaranth. The above results showed sulfonic acid modification endowed Poly([VPImi-SO3H][Cl])-MP with abundant negative charges at certain pH conditions. Thus, the extraction can be achieved by the strong electrostatic attraction between negatively charged Poly([VPImi-SO3H][Cl])-MP and positively charged diquat. Using green vegetables as the sample matrix and magnetic solid-phase extraction as extraction model, the extraction performance of Poly([VPImi-SO3H][Cl])-MP for diquat was studied. Some extraction parameters affecting the extraction efficiency, such as solution pH, adsorbent amount, adsorption time, desorption solvent and its volume, and desorption time were optimized using the single factor experiment method. Under the optimized extraction conditions (30 mg of adsorbent, 15 min of adsorption time, 40 μL of ammonia, 600 μL of acetonitrile-formic acid (9∶1, v/v) as desorption solvent, 1 min of desorption time), the performance, and applicability of the proposed method were investigated by combining magnetic solid-phase extraction, high performance liquid chromatography, and UV-visible detector. Good linearity was observed at contents ranging from 0.2 to 20 μg/g with a correlation coefficient (r) of 0.9981. The limit of detection and limit of quantification based on the signal-to-noise ratio of 3∶1 and 10∶1 were 0.09 and 0.2 μg/g, respectively. The spiked recoveries at three levels of 0.5, 1.0, and 2.5 μg/g were obtained in the range of 82.7%-97.5% with the relative standard deviations of 2.8%-5.0% (n=3). The results showed that the sulfonic acid-functionalized Poly([VPImi-SO3H][Cl])-MP could be employed as a magnetic adsorbent for the quick and effective extraction of diquat, and the proposed method could be used for the determination of diquat from green vegetable samples. It could be anticipated that Poly([VPImi-SO3H][Cl])-MP could be used as an adsorbent for extracting other cationic polar pollutants by adjusting the solution pH. This work provides a new way to construct adsorbents for extracting polar pollutants.

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Polyamidoamine dendrimer-functionalized silica nanocomposite with polydopamine coating for dispersive micro solid-phase extraction of benzoylurea insecticides in water samples CUI Xiaoyan, MA Wenyu, LIN Xiwen, LU Runhua, GAO Haixiang, ZHOU Wenfeng 2022, 40 (10):  929-936.  DOI: 10.3724/SP.J.1123.2022.03012 Abstract ( 109 )   HTML ( 21 )   PDF (6839KB) ( 46 )   Pesticides are used in the agricultural production process to ensure the yield and quality of agricultural products. However, in recent years, environmental pollution issues caused by pesticide residues have sparked widespread concern in society. It is important to develop convenient and efficient approaches to detect and monitor pesticide residues. In this study, targeting benzoylurea insecticides (BUs), polyamidoamine dendrimer-functionalized silica nanocomposite with polydopamine coating (SiO2-PAMAM-PDA) was designed and successfully synthesized. First, monodisperse silica nanoparticles were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in mixed solution of ethanol, water and ammonia. The silane coupling agent (3-aminopropyl)triethoxysilane was then employed to introduce amino groups into the silica. Silica with the zeroth generation of polyamidoamine (PAMAM) modification (SiO2-PAMAM-G0) was obtained through Michael addition reaction of methyl acrylate. Ethylenediamine was added to polymerize with methyl acrylate using an amidation reaction to form the first-generation PAMAM (SiO2-PAMAM-G1). Finally, by polymerizing dopamine under alkaline conditions (pH=8.5), the SiO2-PAMAM-G1 was coated with PDA. Thus, the final product named SiO2-PAMAM-PDA was obtained. The composite was characterized using a transmission electron microscope (TEM) and an increase in surface roughness indicated the successful grafting of PDA coating. Dopamine structure contains abundant benzene rings and amino and hydroxyl groups. It could bind with BUs through multiple secondary interactions, such as hydrogen bond and π-π stacking interaction. Therefore, the introduction of PDA could effectively enhance the affinity of the material toward benzoylurea insecticides. The prepared nanocomposites were used as sorbents in a dispersive micro solid-phase extraction approach (D-μ-SPE). The established approach was employed to extract and enrich the BUs in water samples before high-performance liquid chromatography (HPLC) analysis. Diflubenzuron, triflumuron, hexaflumuron, and teflubenzuron were chosen as target analytes. The following was a typical D-μ-SPE procedure. The prepared adsorbents measuring 40 mg were first dispersed in an 8-mL sample solution containing 150 g/L NaCl. The dispersion was assisted by 120-s vortexing to ensure full contact between the SiO2-PAMAM-PDA and the targets. Next, the adsorbents were separated from the liquid phase by 4-min centrifugation (5000 r/min). Thereafter, the adsorbed benzoylureas were eluted using 1 mL acetonitrile as desorption solvent by 120-s vortexing. Separated by centrifugation, the eluate was dried under a mild nitrogen stream. The solid remains were redissolved in 0.1 mL of acetonitrile, filtered by filter membrane (0.22 μm), and then analyzed by HPLC. The experimental conditions in the D-μ-SPE process could have a great impact on the extraction efficiency. Experimental conditions were optimized using a single factor optimization approach to further enhance the extraction recoveries. The optimized conditions included adsorbent amount, extraction time, desorption solvent type, desorption solvent volume, desorption time, and NaCl addition amount. Under the optimal conditions, a linearity range of 10-500 μg/L and limits of detection (LODs, S/N=3) of 1.1-2.1 μg/L were obtained. The extraction recoveries and relative standard deviations (RSDs) of the four BUs were 82.8%-94.1% and 2.1%-8.0%, respectively. The established approach was compared with reported approaches targeting benzoylurea insecticides. It was discovered that this approach consumed less sample, material, organic solvent, and pretreatment time. It provided a more rapid and green choice for the determination of benzoylurea pesticides. To determine the applicability, the proposed approach was applied to analyze the four benzoylurea insecticides in three river water samples. The real water samples were pretreated using the developed approach ahead of instrumental analysis, and no benzoylurea pesticides residue was detected. Next, standard addition experiments were performed under three spiking levels, including 15, 50, and 200 μg/L. The established approach had good accuracy and feasibility with satisfactory recoveries (69.5%-99.4%) and RSDs (0.2%-9.5%).

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Determination of polychlorinated naphthalenes in soil using accelerated solvent extraction-molecular sieves solid-phase extraction coupled with gas chromatography-tandem mass spectrometry JIN Jing, LIU Hongyuan, XUE Huifu, YANG Jing, QU Chunhua, MA Huilian, CHEN Jiping 2022, 40 (10):  937-943.  DOI: 10.3724/SP.J.1123.2021.12030 Abstract ( 151 )   HTML ( 25 )   PDF (1596KB) ( 80 )   Emerging pollutants (EPs) are chemical substances that are commonly not regulated and can be detected at low or very low concentrations. However, EPs have triggered special concern because their long-term adverse effects on the environment and human health remain unknown. Most EPs show biological toxicity, environmental persistence, and bioaccumulation. Even at low concentrations in the environment, EPs may pose significant environmental and health risks. Therefore, their treatment has been explicitly included in the 14th Five Year Plan for National Economic and Social Development of the People’s Republic of China and the Outline of the Long-term Goals for 2035. Soil is a source of pollutants, and its quality is directly related to economic development, ecological security, and people’s livelihood. At present, China’s soil environmental monitoring system is not perfect, and the ability to monitor these new organic pollutants is lagging. Therefore, to strengthen the supervision of construction and agricultural land soil environments, it is essential to strengthen the soil environment monitoring ability for these EPs and establish a reliable, steady, and economic analysis method, including their separation and analysis methods in soil. Polychlorinated naphthalenes (PCNs) have received considerable attention as emerging halogenated compounds. They were listed in Annexes A and C of the Stockholm Convention on persistent organic pollutants (POPs) in 2015 because of their persistence, multimedia fate, and toxicity. PCNs have now been detected in the surrounding soils. Owing to their trace levels in complex soil, high requirements have been put forward for the pretreatment and instrument analysis of PCNs. This study aims to develop a new method for the selective purification of PCNs in soil, which can not only effectively remove lipids and other interferences in soil but also effectively reduce time, labor, and material costs in the pre-treatment process. Based on the physicochemical properties of the 13X molecular sieve, it was explored to purify soil-extracts as solid-phase extraction (SPE) sorbents. With n-hexane as the loading and rinsing solvent, 10 mL of a dichloromethane/n-hexane mixture (2∶15, v/v) was used to elute the PCNs. Moreover, selective separation of target substances from lipid macromolecules and other interferences could be achieved simultaneously. For the selective separation of PCNs, the average recovery of the internal standard could reach 56.1% to 88.0%. 13X molecular sieves are superior to gel permeation chromatography (GPC) and Florisil SPE, and they exhibit good cleanup efficiency similar to a multilayer silica gel/alumina column (53.0%-117.0%). Although the obtained recoveries are not as high as those obtained with a multilayer silica gel/alumina column, 13X molecular sieves have advantages in terms of simple operation, environmental friendliness, and low cost. Based on these fundamental experiments, accelerated solvent extraction was used to extract targets in soil, molecular sieves were used as SPE sorbents for purification, and GC-MS/MS was employed for PCN analysis. This method was developed as a systematic analytical method for PCNs determination. The method detection limits (MDLs) for PCN homologs were in the range of 0.009-0.6 ng/g. The precision and accuracy of the method were evaluated using spiked matrices. At three spiked levels (4, 10, and 18 ng), the recoveries of PCNs (CN-3, 13, 42, 46, 52, 53, 73, and 75) were 70%-128%, 71%-115%, and 61%-114%, respectively, and the corresponding relative standard derivations were 4.2%-23%, 6.5%-31% and 4.7%-22%. Thus, this method meets the requirements of trace analysis and shows acceptable parallelism, sensitivity, accuracy, and precision, thus being feasible for the analysis of emerging pollutant. The method is expected to play an important role in sample pretreatment in the future, especially for the nationwide investigation of soil pollution.

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Screening of risky substances in sea cucumbers based on gas chromatography-orbitrap high-resolution mass spectrometry MA Chang, CAO Rong, SUN Shuai, ZHANG Haijun, CHEN Jiping, XIONG Zhili, LU Xianbo 2022, 40 (10):  944-951.  DOI: 10.3724/SP.J.1123.2022.04001 Abstract ( 177 )   HTML ( 32 )   PDF (1735KB) ( 78 )   A new method for sample pretreatment using improved QuEChERs was established, and 289 organic pollutants with health risks could be identified and quantified through gas chromatography-orbitrap high-resolution mass spectrometry (GC-Orbitrap HRMS). A high-resolution database of 289 environmental pollutants belonging to ten categories, including organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), phthalates (PAEs), polychlorinated biphenyls (PCBs), and other agricultural chemicals (ACs), was established for the non-targeted screening and quantitative analysis. A simple method for biological sample preparation using improved QuEChERs was proposed by combining a conventional QuEChERs method and a column purification method. After purification using a Florisil column, the lipid content was reduced by 99.9%, which significantly reduced the interference of the matrix effect observed during the analysis. Furthermore, simultaneous high-accuracy qualitative screening and quantitative analysis of the target compounds were performed through high-resolution mass spectrometry (60000 resolution) conducted in the full scan mode. The limits of quantification were 0.56-57.8 pg/g, presenting a large linear range (~106), and the recovery range was 40%-120%. Due to the high-resolution and sensitivity of Q Exactive GC-Orbitrap HRMS, the limits of quantification of the target compounds were significantly lower than those achieved through methods based on conventional chromatography and mass spectrometry. Moreover, ultratrace organic contaminants that cannot be detected by conventional methods can be accurately quantified by the proposed method. Sea cucumber samples collected at the breeding site were analyzed using the proposed high-coverage multi-objective analytical method, and more than 100 types of organic pollutants were detected; the mean contents of PAHs, ACs, PAEs, and OCPs were 157.8, 153.2, 64.4, and 46.4 ng/g dw, respectively, which were higher than those of other pollutants. Some new contaminants, such as 9-chlorofluorene, 5-chloroacenaphthene, and 3-methylcholanthrene, were detected at very low contents for the first time in the sea cucumber samples. The proposed method is simple and efficient, allows the detection of pollutants at very low contents, and provides accurate and reliable results. Thus, this high-coverage multi-objective analytical method can be widely used for broad-spectrum screening and accurate quantification of contaminants in various aquatic products, providing technical support for food safety control.