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Chinese Journal of Chromatography
2021, Vol. 39, No. 9
Online: 08 September 2021

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Advances in application of molecularly imprinted polymers to the detection of polar pesticide residues LI Ting, CHANG Mengmeng, SHI Xianzhe, XU Guowang 2021, 39 (9):  930-940.  DOI: 10.3724/SP.J.1123.2021.03005 Abstract ( 199 )   HTML ( 43 )   PDF (2634KB) ( 150 )   Polar pesticides can be primarily classified as fungicides, herbicides, and insecticides; their rich variety and low cost have led to their extensive utilization in agriculture. However, the overuse of polar pesticides can lead to environmental contamination, such as water or soil pollution, which can also increase the risk of pesticide exposure among human life directly, or indirectly through contact with animal and plant-derived food. There are considerable differences in the physical and chemical properties of polar pesticides, as well as their trace amounts in complex food and environmental samples, posing immense challenges to their accurate detection. As a kind of artificially prepared selective adsorbent, molecularly imprinted polymers (MIPs) possess specific recognition sites complementary to template molecules in terms of the spatial structure, size, and chemical functional groups. With many advantages such as easy preparation, low cost, as well as good chemical and mechanical stability, MIPs have been widely applied in sample pretreatment and the analysis of polar pesticide residues. MIPs are typically used as adsorption materials in solid phase extraction (SPE) methods, including magnetic solid phase extraction (MSPE), dispersed solid phase extraction (DSPE), and stir bar sorptive extraction (SBSE). To rapidly detect polar pesticide residues with high sensitivity, MIPs are also used in the preparation of fluorescent sensors and electrochemical sensors. Furthermore, MIPs can be employed as the substrate in surface-enhanced Raman spectroscopy and as the substrate for the ion source in mass spectrometry for polar pesticide residue analysis. Thus far, various molecularly imprinted materials have been reported for the efficient separation and analysis of polar pesticide residues in various complex matrices. However, there is no review that summarizes the recent advances in MIPs for the determination of polar pesticides. This review introduces imprinting strategies and polymerization methods for MIPs, and briefly summarizes some new molecular imprinting strategies and preparation technologies. The application of MIPs in recent years (particularly the last five years) to the detection of polar pesticide residues including neonicotinoids, organophosphorus, triazines, azoles, and urea is then systematically summarized. Finally, the future development direction and trends for MIPs are proposed considering existing challenges, with the aim of providing reference to guide future research on MIPs in the field of polar pesticide residue detection.

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Research progress in application of metal-organic framework-derived materials to sample pretreatment ZHANG Wenmin, LI Qingqing, FANG Min, GAO Jia, CHEN Zongbao, ZHANG Lan 2021, 39 (9):  941-949.  DOI: 10.3724/SP.J.1123.2021.05017 Abstract ( 133 )   HTML ( 30 )   PDF (902KB) ( 136 )   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.

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Applications of chromatography in giant complex drug-organism system JIA Pu, BIAN Yangyang, BAI Yajun, MENG Xue, GAO Shuomo, ZHAO Ye, CAI Yujie, ZHENG Xiaohui 2021, 39 (9):  950-957.  DOI: 10.3724/SP.J.1123.2021.06021 Abstract ( 122 )   HTML ( 30 )   PDF (1912KB) ( 71 )   Chromatography is an important branch of analytical chemistry that focuses on the separation and analysis of complex structures. Following more than 100 years of development and improvement, chromatography theory and technology have gradually become sophisticated. It has become a coalition of science, technology, and art. Recently, chromatography has been successfully used in combination with mass spectrometry, nuclear magnetic resonance spectroscopy, and atomic emission spectroscopy. Chromatography and the combination with other techniques has significantly improved the analysis of complex systems, such as the environment, food, petrochemicals, biological specimens, and medicine. As one of the oldest healing systems, Traditional Chinese Medicine (TCM) has served to maintain the health of people in China and worldwide for thousands of years. Therefore, it has become a core representative of traditional Chinese culture. In the past two years, TCM has been widely used to treat COVID-19, especially in patients with mild symptoms. Recently, Chinese government emphasized the inheritance and innovation of TCM and stepped up efforts to promote its modernization. TCM includes herbal medicine, acupuncture, moxibustion, massage, food therapy, and physical exercise, such as Tai Chi. In most cases, the patients are administered a mixture of TCM formulas containing more than two herbal medicines, resulting in a highly complicated compound mixture. There is no doubt that long-term clinical practices have demonstrated the safety and therapeutic effect of TCM. However, the compound mixture must be simplified to identify the active compounds. This is mainly because of the existence of carcinogenic compounds, pesticides, and heavy metal residues introduced through plantation and production processes. Moreover, enzymes within the human system generate further new compounds in response to the entry of the TCM containing thousands of components. Consequently, the complex TCM and organism systems interact with each other, constituting a giant complex drug-organism system. The analysis of this giant complex system is acknowledged as a key aspect in the modernization process of TCM. In the last 20 years, many studies have been conducted to screen and identify effective compounds in TCM. These effective compounds can be either the original compounds or new metabolic components generated in vivo. All these efforts are aimed at simplifying the components of TCM and elucidating the therapeutic mechanism. It is well known that chromatography can provide technical support for complex systems owing to its unique advantage of outstanding separation and analysis capabilities. Therefore, chromatography and its combination with other technologies have become mainstream technologies for promoting the compilation of molecular structure, information, digitalization, and modernization of TCM. This paper reviews the research and application of chromatography and combination technologies in a giant complex TCM formula-organism system. Furthermore, the authors briefly introduce and summarize the understanding, research ideas, and activities of the authors’ team on the modernization of TCM. “Liang Guanxi” and “He strategy” are proposed as novel strategies for studying the giant complex drug-organism system. A distinguished technology integrated with mathematical model of causal relation, combined receptor chromatography, identification of chemical molecular structure and evaluating of pharmacological activities was established. It was successfully employed to determine the core effector-response substances of “Liang Guanxi” herb pairs in a giant complex drug-organism system. Subsequently, utilizing the proposed technology of Combination of Traditional Chinese Medicine Molecular Chemistry, the author’s team designed and developed four series of innovative drugs. Inspired by the hundred years of chromatography history and thousands of years of TCM culture, the future development of chromatographic technology is expected. Furthermore, the mechanisms of TCM in medical healthcare, prevention, and treatment of diseases are likely be explained through chromatography, leading to a new strategy to realize the molecularization and digitalization of TCM, which is beneficial to the development of original new drugs.

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Progress of sample preparation and analytical methods of dried fruit foods ZHOU Lihui, XIAO Xiaohua, LI Gongke 2021, 39 (9):  958-967.  DOI: 10.3724/SP.J.1123.2021.06030 Abstract ( 172 )   HTML ( 30 )   PDF (1163KB) ( 110 )   Dried fruit foods, including nuts and preserved fruits, are favored by consumers and are rich in protein, lipids, minerals, vitamins, and other nutrients. However, these food products can be contaminated by pesticide residues, heavy metals, mycotoxins, and additives during growth, processing, storage, and transportation. The presence of such pollutants in excess of a certain limit will lead to food safety problems. Therefore, it is of great economic and social significance to strengthen the quality supervision of dried fruit foods. However, these foods have a complex matrix and low concentrations of various harmful substances, which necessitates efficient and appropriate sample preparation methods as well as rapid, accurate detection methods. In the present article, the sample preparation and analytical methods for harmful substances in dried fruit foods since 2010 are reviewed. The sample preparation methods are classified as field-assisted extraction, phase separation, and derivatization and extraction methods. The field-assisted extraction method is based on the action of an external field (synergistic) such as ultrasonic or microwave fields to increase the dissolution rate of hazardous substances in dried fruits and improve the extraction efficiency. Phase separation methods such as solid-phase extraction, dispersive solid-phase extraction and solid-phase microextraction are commonly used as sample preparation methods for dried fruit samples, because of the advantages of low solvent consumption and wide analysis range. Moreover, this paper discusses the progress of various analytical methods for these hazardous substances in dried fruits, including conventional laboratory methods such as chromatography, atomic spectroscopy, inorganic mass spectrometry, and electrochemical analysis, as well as rapid detection techniques suitable for field analysis. Laboratory testing has the advantages of high accuracy, high sensitivity, and low detection limits. However, it has the disadvantages of complicated preparation, long analysis time, and difficult operation. Rapid detection technology speeds up the analytical speed, has operational simplicity, and saves analysis time. The complexity of the food matrix, which easily interferes with the sample matrix, low selectivity, and difficulty in accurate quantification, it is necessary to minimize cases of incorrect or erroneous detection. Therefore, rapid detection of harmful substances in dried fruit foods is possible by optimizing the sample pretreatment methods and detection technologies, and by seeking new (especially, on-site) detection technologies. Prospects on the development of selective and non-destructive sample preparation methods and automated, high-throughput, rapid detection methods in dried fruit food analysis are presented. The development of new, green rapid sample pretreatment methods and technical products that integrate separation, enrichment, and detection as well as the construction of accurate and sensitive rapid detection methods are expected to become the development trend in the analysis of harmful substances in dried fruit foods.

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Microfluidic strategies for separation and analysis of circulating exosomes CHEN Wenwen, GAN Zhongqiao, QIN Jianhua 2021, 39 (9):  968-980.  DOI: 10.3724/SP.J.1123.2021.07005 Abstract ( 441 )   HTML ( 43 )   PDF (5157KB) ( 215 )   Exosomes are membrane-bound nanovesicles that are secreted by most types of cells and contain a range of biologically important molecules, including lipids, proteins, ribonucleic acids, etc. Emerging evidences show that exosomes can affect cells’ physiological status by transmitting molecular messages among cells. As such, exosomes are involved in various pathological processes. Studying exosomes is of great importance for understanding their biological functions and relevance to disease diagnosis. However, it is difficult to separate and analyze exosomes due to their small size, and because their density is similar to that of bodily fluids. Traditional methods, including ultracentrifugation and ultrafiltration are time-consuming and require expensive equipment. Other methods for exosome separation, including immunoaffinity-based methods, are expensive and rely heavily on specific antibodies. Precipitation-based methods do not yield acceptable purity for downstream analysis, due to polymer contamination. Thus, urgent demand exists for a portable, simple, affordable method for exosome separation. Microfluidic chip technology offers a potential platform for separation and detection of exosomes, with several remarkable characteristics, including low sample consumption, high throughput, and easy integration. This paper provides an overview of current microfluidic strategies for separation and analysis of circulating exosomes. In our introduction to exosome separation, we divide existing separation methods into two categories. Category one is based on exosome physical properties, and includes membrane filtration, nano-column array sorting, and physical isolation. The other is immune capture, which is based on biochemical characteristics of exosomes, and includes fixed base immune capture and unfixed base immune capture. In our introduction to exosome analyses, some commonly used methods, including western blotting, scanning electron microscopy, and flow cytometry are briefly described. Some new systems, which combine microfluidic technology with fluorescence, electrochemical sensing, surface plasmon resonance, or other multimodal analysis methods for integrated detection of exosomes are then described in detail. Finally, the challenges faced by microfluidic technology in improving exosome purity and making systems more portable are analyzed. Prospects for application of microfluidic chips in this area are also discussed. With the rapid development of micro/nano-manufacturing, new materials, and information technology, microfluidic exosome separation and analysis systems will become smaller, more integrated, and more automated. Microfluidic chip technology will play important roles in exosome separation, biochemical detection, and mechanism analysis.

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Recent advances in functionalized magnetic nanomaterials for glycoprotein and glycopeptide enrichment GAO Wenjie, BAI Yu, LIU Huwei 2021, 39 (9):  981-988.  DOI: 10.3724/SP.J.1123.2021.08012 Abstract ( 228 )   HTML ( 363 )   PDF (2191KB) ( 129 )   Protein glycosylation is among the most common and important post-translational modifications, and plays an important regulatory role in many biological processes, including signal transduction, protein translation, and immune response. Abnormal protein glycosylation is also associated with numerous diseases, suggesting that glycoproteins may offer an array of useful disease biomarkers. Mass spectrometry (MS) has become an important analytical tool in glycoproteomics. However, the low abundance and weak ionization efficiency of glycopeptides have hindered direct mass spectrometric analyses, which remain considerably challenging. Glycoprotein and glycopeptide enrichment from complex biological samples is an important step in glycoproteomics. Diverse methods have recently been developed for specific glycoprotein and glycopeptide enrichment, including hydrophilic interaction liquid chromatography (HILIC), lectin affinity chromatography, boronate affinity chromatography, and hydrazide functional affinity chromatography. A variety of enrichment materials designed for the above strategies have been developed to meet the requirement of enriching low abundance glycoproteins and glycopeptides in complex samples. Magnetic solid phase extraction (MSPE) is an efficient sample pretreatment technology that offers advantages of simple operation, low cost, and high extraction efficiency. Functionalized magnetic nanomaterials have been widely used as adsorbents in glycoproteome studies. Since magnetic adsorbent is a key factor in MSPE, in this review, the preparation of magnetic nanomaterials functionalized with sugars, ionic liquids, lectins, boronate affinity ligands, metal organic frameworks, and covalent organic frameworks, and their applications in glycoprotein and glycopeptide enrichment are summarized. These functional magnetic nanomaterials possess high specific surface area and a large number of active adsorption sites, allowing different enrichment mechanisms, including HILIC, lectin affinity chromatography, and boronate and hydrazide functional affinity chromatography. These functional magnetic nanomaterials are mainly used to enrich glycoproteins and glycopeptides in serum, plasma, cells, tissues, saliva and other biological samples. Nearly 90 papers published in the last decade from the Science Citation Index (SCI) and Chinese core journals have been cited in this paper. Finally, the development and prospects of magnetic nanomaterials in glycoprotein and glycopeptide enrichment are also discussed.

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Quality analysis of Ziziphi Spinosae Semen extracts based on high performance liquid chromatography quantitative fingerprint and ultra-high performance liquid chromatography-tandem mass spectrometry quantification GUO Xiujie, LI Haoqiu, FENG Haotian, QI Huawen, ZHANG Lu, XU Wei, WU Yanjuan, WANG Chaoran, LIANG Xinmiao 2021, 39 (9):  989-997.  DOI: 10.3724/SP.J.1123.2021.06019 Abstract ( 214 )   HTML ( 38 )   PDF (2558KB) ( 121 )   Ziziphi Spinosae Semen is the dried seeds of Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chou, and its extract has broad application prospects in the development of sleep-aid functional foods. However, the quality parameters of Ziziphi Spinosae Semen extracts currently available in the market are not uniform and there is a lack of unified standards. Therefore, it is important to establish an accurate and comprehensive method for quality evaluation. In view of the problems that the UV responses of flavonoids and saponins in the Ziziphi Spinosae Semen extracts vary dramatically and the saponin content in Ziziphi Spinosae Semen water extract is very low, high performance liquid chromatography (HPLC) was used to establish the fingerprint and quantify spinosin. The separation was carried out on a Waters XSelect HSS C18 column (250 mm×4.6 mm, 5 μm), and the mobile phase was acetonitrile-0.1% (v/v) phosphoric acid aqueous solution for gradient elution. The eight common peaks in the fingerprint of the Ziziphi Spinosae Semen extracts, identified by HPLC-quadrupole time-of-flight mass spectrometry, were attributed to flavonoids by reference substance identification, literature comparison, and high-resolution mass spectrometry data analysis. Semi-quantitative analysis of seven flavonoids and quantitative analysis of spinosin were conducted using the established HPLC quantitative fingerprint. The contents of jujuboside A and jujuboside B were determined by ultra-high performance liquid chromatography-triple quadrupole mass spectrometry. Chromatographic separation was performed on a Waters ACQUITY UPLC BEH C18 column (50 mm×2.1 mm, 1.7 μm) by gradient elution using a mobile phase of acetonitrile-0.1%(v/v) formic acid aqueous solution. The target compounds were analyzed in multiple reaction monitoring mode with positive electrospray ionization. The semi-quantitative and quantitative data of the above-mentioned 10 components are displayed in the form of radar. Using the above methods, three batches of Ziziphi Spinosae Semen water extracts prepared in the laboratory and 15 batches of extract samples obtained from 15 suppliers were analyzed and compared. The results showed that although the raw materials of three batches of Ziziphi Spinosae Semen water extracts prepared in the laboratory were from different enterprises, the overall difference was not significant. However, the component contents of the samples provided by different manufacturers were greatly different, suggesting that there are some problems associated with the different manufacturers, such as dilution of excipients, adulteration of Ziziphi Mauritianae Semen, alcohol extraction, purification, and enrichment. For example, the representative composition contents in the Ziziphi Spinosae Semen extracts obtained from manufacturers B, C, E, F, G, H, I, and O were low, which were approximately 1/10 of corresponding contents in the normal water extracts prepared in the laboratory. It is speculated that to reduce the unit price of the product, the manufacturer used fewer raw materials or a large number of auxiliary materials to dilute the Ziziphi Spinosae Semen extracts. The contents of some flavonoids in the Ziziphi Spinosae Semen extract from manufacturer N were slightly higher than that in the self-preparation Ziziphi Spinosae Semen water extract, but it did not contain jujuboside A; thus, it was speculated that the Ziziphi Mauritianae Semen might be used for extraction. The contents of 10 components in the Ziziphi Spinosae Semen extract obtained from manufacturer D were all higher than the corresponding ones in the self-preparation Ziziphi Spinosae Semen water extract. Combined with the quality label of total saponin content > 20% and poor water solubility, it was speculated that the product might be prepared by alcohol extraction or purified and enriched by using resin. These results provided the basis for the enterprise to establish internal control quality standards for Ziziphi Spinosae Semen extracts and to select qualified suppliers.

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Preparation of melamine-functionalized porous organic polymer and its adsorption properties for methyl orange ZHANG Chong, GUO Yun, PENG Zifang, ZHANG Wenfen, ZHANG Shusheng 2021, 39 (9):  998-1005.  DOI: 10.3724/SP.J.1123.2021.06016 Abstract ( 177 )   HTML ( 22 )   PDF (4327KB) ( 107 )   In this work, a polymer precursor was first synthesized using p-terphenyl (TP) and terephthaloyl chloride (TC) as monomers. Then, cross-linking was realized by means of a Schiff base reaction with melamine (MA) as a modifier to obtain an amine-functionalized porous organic polymer TP-TC-MA. The synthesized polymers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and point of zero charge (pHpzc) measurements, as well as on the basis of nitrogen adsorption-desorption isotherms. Adsorption experiments were carried out to evaluate the adsorption properties of TP-TC-MA for methyl orange (MO), a typical anionic azo dye that has widespread industrial application. The amount of MO adsorbed on TP-TC-MA was evaluated by ultraviolet-visible (UV-Vis) spectroscopy at a wavelength of 463 nm. Microscopic analysis revealed that the as-synthesized polymer had an aggregated particle-shaped structure. XRD spectra confirmed that TP-TC-MA was an amorphous polymer, consistent with the results of high-resolution TEM experiments. The Brunauer-Emmett-Teller (BET) specific surface area and total pore volume of TP-TC-MA were determined as 708.5 m 2/g and 0.556 cm3/g, respectively. The measured pHpzc of TP-TC-MA was 4.0, probably because of the abundant nitrogen-containing groups provided by MA. The factors affecting adsorption, such as pH, adsorbent dosage, contact time, initial pollutant concentration, and ionic strength, were investigated. Because of the protonation of the N-atom in TP-TC-MA, the pH had a strong impact on the adsorption of MO. The removal efficiency could be maximized at the optimized pH of 3.0. The adsorption equilibrium isotherm, measured at 25 ℃ and a concentration of 50-500 mg/L, showed that the MO adsorption over TP-TC-MA followed the Langmuir isotherm, with a maximum adsorption capacity of 156.3 mg/g. The modeling of the experimental adsorption data was consistent with the pseudo-second-order kinetic model, which indicated fast adsorption and chemisorption as the dominant mechanism. With increasing ionic strength, the adsorption of MO slightly decreased, suggesting a partial antagonistic ion effect. Results of the selectivity study revealed that TP-TC-MA was more selective toward MO than methylene blue (MB), which indicated that electrostatic interactions played a significant role during the adsorption progress. Five adsorption-desorption cycles showed that TP-TC-MA could be regenerated without significant deterioration of its adsorption efficiency, indicating that it has good stability and reusability. The observed adsorption performance indicated that this MA-modified porous organic polymer offers prospects for further research and application in the treatment of dye-containing wastewaters.

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Fingerprint establishment and multi-indicator quantitative analysis of fermented Cordyceps powder and products CAO Wen, HONG Liang, YANG Ming, LI Shaoping, ZHAO Jing 2021, 39 (9):  1006-1011.  DOI: 10.3724/SP.J.1123.2021.06022 Abstract ( 162 )   HTML ( 38 )   PDF (1293KB) ( 86 )   Supporting Information Currently, guanosine, adenosine, and uridine contents are specified as the quality criteria for related products in the quality standards for fermented Cordyceps powder preparations included in the 2020 edition of Chinese Pharmacopoeia. However, there are many other nucleosides in fermented Cordyceps powder, whose effect on the quality control has not yet been discussed. In this study, an ultra-performance liquid chromatography-ultraviolet detection (UPLC-UV) method was used for the quantitative analysis of 9 nucleosides (uracil, cytidine, guanidine, uridine, adenine, inosine, guanosine, thymidine, and adenosine) in 19 batches of fermented Cordyceps powder samples and products, and the corresponding fingerprints were established. In addition, a method for analyzing the index components was proposed based on statistics. By optimizing the sample extraction method, ultrasound-assisted extraction was selected to process 19 batches of samples. Chromatographic analysis was performed on an Agilent Eclipse Plus C18 column (150 mm×4.6 mm, 3.5 μm) using methanol and water as the mobile phases under gradient elution. The method was validated based on the calibration curves, accuracy, precision, repeatability, and recovery. The fingerprints of the 19 batches of samples were established, and 16 common peaks were obtained. Among them, nine nucleoside peaks were identified by standards, and their concentrations were determined by the external standard one-point method. Similarity evaluation of the fingerprints was conducted; the similarities of the 19 batches of samples were greater than 0.9. Then, chemical pattern recognition was performed. The same classification results were obtained by hierarchical clustering analysis (HCA) and principal component analysis (PCA). Thus, the samples could be segregated into five classes, and the fermented Cordyceps powders were classified as two types with different fermentation processes. Xinganbao capsules, Bailing capsules and Ningxinbao capsules were each separately classified into one class. This indicated that the chemical recognition pattern could effectively distinguish between the fermented Cordyceps powder and different products. PCA was used to calculate the weight value of each common peak for the first time, and the index components among the samples were selected according to the weight value. Finally, the selected index components were used to re-cluster the samples. The results were consistent with those obtained on the basis of the 16 common peaks, thus verifying the rationality of the index components. Therefore, uridine, guanosine, adenosine, adenine, and uracil are recommended for use as evaluation indicators for fermented Cordyceps powder and products, allowing for better distinction between the products on the market. In summary, the combination of liquid chromatographic fingerprints and chemical pattern recognition can provide a simple and reliable method for the analysis and quality control of fermented Cordyceps powder and products.

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Solid phase microextraction-high performance liquid chromatography of fluorinated covalent organic polymer to determine eugenol anesthetics in aquatic products WANG Xingyi, CHEN Yanlong, LI Gongke 2021, 39 (9):  1012-1020.  DOI: 10.3724/SP.J.1123.2021.06027 Abstract ( 148 )   HTML ( 36 )   PDF (3894KB) ( 100 )   Fluorinated covalent organic polymers (F-COPs) constitute a new class of porous materials with a topological structure, large surface area, and potential superiority over other types of polymers in sample preparation. In this study, a F-COP was rapidly synthesized by a simple Schiff-based reaction using 2,3,5,6-tetrafluoroterephthalaldehyde (TFA) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) as monomers, and by adding scandium (Ⅲ) triflate (Sc(OTf)3) as the metal catalyst at room temperature. The prepared F-COP was applied as a coating adsorbent for solid phase microextraction (SPME) to enrich three kinds of eugenol anesthetics in aquatic products. The extraction performance of an enrichment medium is an important factor for practical application in real analytical projects. This F-COP adsorbent with rich π-stacking electrons contained abundant phenyl rings and imine (-C=N) groups throughout the molecular framework. The adsorption mechanism was explored and discussed based on the π-π affinity and hydrogen bonding interaction, which contributed to its strong recognition affinity to targets. The F-COP was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, and scanning electron microscopy (SEM). The results indicated that the novel F-COP-SPME bar exhibited a rough and porous surface structure, good preparation reproducibility, and high stability. High performance liquid chromatography (HPLC) was performed with an ultraviolet-visible (UV-vis) wavelength detector. A Diamonsil plus C18 column (250 mm×4.6 mm, 5 μm) was used as the analytical column. The mobile phase comprised 60% methanol and 40% ultrapure water, and was flowed at 0.800 mL/min. The injected volume of the sample was 20.0 μL. The column temperature was maintained at 30 ℃ and the detection wavelength was set to 280 nm. Further, the SPME conditions (including extraction time, stirring rate, desorption solvent, and desorption time) that influenced the extraction efficiencies of the eugenol anesthetics were investigated in detail. Thus, the optimized F-COP-SPME bar conditions were established as follows: extraction time: 30 min; stirring rate: 700 r/min; desorption solvent: acetonitrile; desorption time: 10 min. By combining F-COP-based SPME with HPLC-UV analysis, an effective method was developed for the extraction and determination of eugenol, eugenyl acetate, and methyl eugenol residues in aquatic products. The method demonstrated good linearity in the range of 10-1000 μg/L for eugenol and eugenyl acetate, and 10-1500 μg/L for methyl eugenol, with correlation coefficients (r2) greater than 0.9961, low limits of detection (2.9-4.5 μg/kg, S/N=3), and excellent precision (relative standard deviations lower than 8.7%, n=5). Finally, the method was applied for the effective extraction of three kinds of eugenol anesthetics from tilapia and shrimp samples. The obtained recoveries were in the range of 76.7%-98.7% and 80.3%-104% with relative standard deviations of 8.5%-11.8% and 8.6%-12.4% (n=5), respectively. These results demonstrated that the F-COP is promising for use as an adsorbent in SPME for the determination of eugenol anesthetics in aquatic products. The developed method was suitable for the qualitative and quantitative determination of three kinds of eugenol anesthetics in aquatic products, yielding a satisfactory purification effect and sensitivity.

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Effects of buffer salt types and non-counter ions of ion-pair reagents on the retention behavior of strongly ionized acid compounds in ion-pair reversed-phase liquid chromatography LIU Xiaolan, GAO Wei, LIANG Chao, QIAO Junqin, WANG Kang, LIAN Hongzhen 2021, 39 (9):  1021-1029.  DOI: 10.3724/SP.J.1123.2021.06044 Abstract ( 171 )   HTML ( 25 )   PDF (1774KB) ( 99 )   Ion-pair reversed-phase liquid chromatography (IP-RPLC) enhances separation by adding ion-pair reagents to the mobile phase, thereby improving the retention of oppositely charged solutes. IP-RPLC is primarily used for the separation and analysis of strongly ionized compounds. In IP-RPLC, researchers often focus more on the influence of the counter-ion type and concentration, buffer salt concentration and pH, and column temperature, on the retention behavior of solutes. However, the effects of the buffer salt type and non-counter ions in ion-pair reagents on the retention behavior of solutes have rarely been investigated. Accordingly, in this work, the effects of buffer salt types and non-counter ions on the retention behavior of strongly ionized compounds were investigated by IP-RPLC using 14 sulfonic acid compounds as model compounds. Experiments were performed using a silica-based C18 column with methanol as the organic modifier. In the first type of experiment, tetrabutylammonium bromide was kept unchanged as the ion-pair reagent in the mobile phase, and ammonium dihydrogen phosphate, ammonium chloride, and ammonium acetate were used as buffer salts, respectively. The retention factor (k) was obtained at different methanol ratios, and linear solvent strength (LSS) models were established to determine the log kw (logarithm of retention factors of solutes when 100% aqueous phases were used as the mobile phase) and S (intercept of the LSS model) values of each solute. All solutes exhibited the highest log kw with the ammonium chloride buffer system; most compounds also exhibited the highest S values with this system, except for 1,5-naphthalenedisulfonic acid, 4-methylbenzenesulfonic acid, 5-amino-2-nanphthalenesulfonic acid, and 4-hydroxybenzenesulfonic acid. However, the chromatographic hydrophobic indices (CHIs, log kw/S) of the solutes with different buffer salts were approximately equal. In the second type of experiment, ammonium dihydrogen phosphate was kept unchanged as the buffer salt in the mobile phase, and tetrabutylammonium bromide, tetrabutylammonium dihydrogen phosphate, tetrabutylammonium hydrogen sulfate, tetrabutylammonium nitrate, and tetrabutylammonium acetate were used as ion-pair reagents, respectively. Almost all solutes exhibited the highest S with the tetrabutylammonium acetate system, indicating that weakly ionized anions (such as acetate ions) in ion-pair reagents will improve the S values of sulfonic acid compounds. Interestingly, the CHIs of the solutes were almost the same for solutes with different non-counter ions. These results suggest that both, the buffer salt types and non-counter ions, influence the log kw and S values of sulfonic acid compounds. Comparison of the retention behavior of solutes with different mobile phases suggested ion-pair mechanisms as well as dynamic ion-exchange mechanisms plays role in the IP-RPLC retention of sulfonic acid compounds. In addition, with all the experimental mobile phases, the apparent n-octanol/water partition coefficient (log D) presented a good linear correlation with log kw, S, and CHI, respectively, by the introduction of structure-related descriptors such as charge (ne), Abraham solvation parameters (A and B), and the polar surface area (PSA). Considering the differences in the log kw and S values obtained with different buffer salts and non-counter ions, the CHIs were relatively stable; therefore, the CHI is more suitable for establishing a quantitative structure-retention relationship (QSRR) model in IP-RPLC, compared to log kw and S.

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Development of a portable micro-liquid chromatograph FU Qiang, YANG Limin, WANG Qiuquan 2021, 39 (9):  1030-1037.  DOI: 10.3724/SP.J.1123.2021.06029 Abstract ( 234 )   HTML ( 31 )   PDF (4019KB) ( 92 )   Portable analytical instruments find extensive application in on-site examination because of their significant advantages: these instruments are convenient and easy-to-carry, leading to high time-effectiveness, and involve low reagent consumption. We report a portable micro-liquid chromatograph (p-μLC) that was designed and fabricated in our laboratory. The p-μLC integrates homemade dual large-thrust syringe pumps for delivering the mobile phase, a capillary polymer monolithic column as the stationary phase for the separation of the target analytes, and a specially designed dual-functional optical-fiber microflow-cell for online detection. The dual-thrust syringe pumps can realize isocratic and/or gradient elution as well as reloading of the mobile phase, with flow rates ranging from 0.025 μL/min to 5.6 mL/min and the maximum working pressure of 4.5 MPa. The polymethacrylate based C-18 monolithic column facilitates the separation of small organic molecules and biomacromolecules. A homemade high-power light emission diode (LED) light source and a modified xenon flash lamp are assembled as the light source module. The dual-functional detector consists of an optical fiber microflow-cell with a self-focusing lens and a light-guiding capillary, light source module, and a small-sized grating spectrometer with an output wavelength range of 400-680 nm for the LED light source and 220-700 nm for the xenon flash lamp, enabling online detection of the absorption and fluorescence spectra of the analytes from 220 to 700 nm. A bifurcated optical fiber bundle is prepared and used to connect the light source, microflow-cell, and grating spectrometer so that the incident light leading-in and the fluorescence/scatting light leading-out can be realized simultaneously. The junction end of the bifurcated optical fiber bundles connects to one end of the light path of the microflow-cell, and a straight-through optical fiber connects another end of the microflow-cell. In the UV-Vis absorption mode, the straight-through optical fiber reads out the transmitted light, while in the fluorescence mode, the excitation light beam from the light source irradiates the sample solution in the flow-cell via one branch of the bifurcated optic fiber bundles. The fluorescence leading-out via the other branch of the bifurcated optical fiber bundles in the opposite direction of the excitation light beam is read out by the spectrometer. All the large-thrust syringe pumps and flow-path, capillary monolithic column, and optical fiber mediated flow-cell detection as well as controlling modules are installed in a suitcase with a total weight of less than 8 kg. The p-μLC is powered by DC 12V 3A or 18650 lithium battery pack and controlled by a panel computer with a custom-built windows-based chromatography workstation software for data acquisition. When using the home-made polymethacrylate based C-18 monolithic capillary column (530 μm ID×200 mm in length), the mixed alkylbenzenes can be separated and detected in an isocratic elution mode. The separation efficiency is comparable to that obtained with a commercially available HPLC.