List of Issues

Chinese Journal of Chromatography
2021, Vol. 39, No. 8
Online: 08 August 2021

Previous Issue    Next Issue



For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Mini-reviews

Select

Application of novel quantum dot-based molecularly imprinted fluorescence sensor in rapid detection MA Jiaxin, LIAN Ziru, HE Cheng, WANG Jiangtao, YU Rencheng 2021, 39 (8):  775-780.  DOI: 10.3724/SP.J.1123.2021.02025 Abstract ( 215 )   HTML ( 228 )   PDF (851KB) ( 145 )   A critical need in analytical chemistry is the efficient fabrication of selective and sensitive sensors to detect trace analytes in complicated samples. In recent years, fluorescence analysis has been widely used in environmental research and the life sciences due to its high sensitivity and simple operation. Quantum dots (QDs) are a new type of fluorescent nanomaterials. Owing to the quantum confinement effect, QDs possess excellent optical properties such as strong anti-bleaching ability, a narrow excitation and emission band, and tunable emission wavelength. As a hot labeling material, QDs are suitable for use in surface-modified analytical sensors employed in fields such as analytical chemistry, biology, and medicine. However, QD materials have a notable disadvantage, in that the actual sample matrix may contain some interferents with luminescent responses similar to those of the target; this decreases the selective ability of the fluorescence sensor. The surface modification of QDs via the molecular imprinting technique (MIT) is a promising solution to overcome this drawback. Molecularly imprinted polymers (MIPs) are a kind of “bionic” material that can carry out specific recognition and selective adsorption and hence, possess the unique properties of recognition specificity, structural predictability, good reproducibility, and excellent stability. Accordingly, MIPs have been widely employed in sensors as well as for drug delivery, catalysis, and solid phase extraction. Notably, QD-based molecularly imprinted fluorescence sensors combine the advantages of QDs and the MIT. Owing to their specific selectivity and high sensitivity, such sensors have been extensively developed for environmental monitoring, food detection, and biological analysis. However, there remain challenges associated with the preparation and application of the sensors: (i) single recognition: it is important to develop a composite sensor that can detect multiple target analytes from the actual samples at the same time during practical application; (ii) poor hydrophilicity: the actual sample is usually a liquid matrix; hence, it is imperative to determine an approach for improving the hydrophilicity of the sensor; (iii) the accuracy of fluorescence response and the resolution of visual detection need to be further improved; (iv) imprinting: it remains challenging to imprint biological macromolecules, viruses, and bacteria. Thus far, many researchers have made progress with regard to the preparation and application of the sensors. Accordingly, this work reviews approximately 20 papers published by the American Chemical Society, Elsevier, and other databases in the last five years to highlight progress in novel preparation methods and practical applications of QD-based molecularly imprinted fluorescence sensors for the sensitive analysis and rapid detection of trace substances. First, according to the different numbers of emission peaks in the fluorescence spectrum, three kinds of QD-based molecularly imprinted fluorescence sensors are introduced and the related recognition mechanisms are explained. Second, according to the different substances to be detected, this mini-review summarizes the latest research progress in sensors for the detection of ions, organic small molecules, biological macromolecules, as well as for the analysis of bacteria and viruses. Finally, existing challenges associated with the preparation and application of the sensors, as well as future development trends, are discussed.

Reviews

Select

Recent advance of new sample preparation materials in the analysis and detection of environmental pollutants FENG Juanjuan, JI Xiangping, LI Chunying, SUN Mingxia, HAN Sen, FENG Jiaqing, SUN Haili, FENG Yang, SUN Min 2021, 39 (8):  781-801.  DOI: 10.3724/SP.J.1123.2021.02030 Abstract ( 385 )   HTML ( 231 )   PDF (1629KB) ( 238 )   To successfully analyze complex samples and detect trace targets, sample pretreatment is essential. Efficient sample pretreatment techniques can remove or reduce interference from the sample matrix. It can also enrich analytes, thereby improving analytical accuracy and sensitivity. In recent years, various sample preparation techniques, including SPE, magnetic dispersion SPE, pipette tip SPE, stir bar extraction, fiber SPME, and in-tube SPME, have received increasing attention in environmental analysis and monitoring. The extraction efficiency mainly depends on the type of adsorbent material. Therefore, the development of efficient adsorbents is a crucial step toward sample preparation. This review summarizes and discusses the research advances in extraction materials over recent years. These extraction materials contain inorganic adsorbents, organic adsorbents, and inorganic-organic hybrid materials such as graphene, graphene oxide, carbon nanotubes, inorganic aerogels, organic aerogels, triazinyl-functionalized materials, triazine-based polymers, molecularly imprinted polymers, covalent organic frameworks, metal-organic frameworks, and their derivatives. These materials have been applied to extract different types of pollutants, including metal ions, polycyclic aromatic hydrocarbons, plasticizers, alkanes, phenols, chlorophenols, chlorobenzenes, polybrominated diphenyl ethers, perfluorosulfonic acids, perfluorocarboxylic acids, estrogens, drug residues, and pesticide residues, from environmental samples (such as water and soil samples). These sample preparation materials possess high surface areas, numerous adsorption sites, and allow extraction via various mechanisms, such as π-π, electrostatic, hydrophobic, and hydrophilic interactions, as well as hydrogen and halogen bond formation. Various sample pretreatment techniques based on these extraction materials have been combined with various detection methods, including chromatography, mass spectrometry, atomic absorption spectroscopy, fluorescence spectroscopy, and ion mobility spectroscopy, and have been extensively used for the determination of environmental pollutants. The existing challenges associated with the development of sample preparation techniques are proposed, and prospects for such extraction materials in environmental analysis and monitoring are discussed. Major trends in the field, including the development of efficient extraction materials with high enrichment ability, good selectivity, excellent thermal stability, and chemical stability, are discussed. Green sample pretreatment materials, environmentally friendly synthesis methods, and green sample pretreatment methods are also explored. Rapid sample pretreatment methods that can be conducted within minutes or seconds are of significant interest. Further, online sample pretreatment and automatic analysis methods have attracted increasing attention. Besides, real-time analysis and in situ detection have been important development directions, and are expected to be widely applicable in environmental analysis, biological detection, and other fields. Modern synthesis technology should be introduced to synthesize specific extraction materials. Controllable preparation methods for extraction materials, such as the in situ growth or in situ preparation of extraction coatings, will acquire importance in coming years. It will also be important to adopt high-performance materials from other fields for sample pretreatment. Organic-inorganic hybrid extraction materials can combine the advantages both organic materials and inorganic materials, and mutually compensate for any disadvantages. Extraction materials doped with nanomaterials are also promising. Although existing sample pretreatment techniques are relatively efficient, it is still imperative to develop novel sample preparation methods.

Select

Applications of microfluidic paper-based chips in environmental analysis and detection ZHANG Yu, QI Ji, LIU Feng, WANG Ning, SUN Xiyan, CUI Rong, YU Jialuo, YE Jiaming, LIU Ping, LI Bowei, CHEN Lingxin 2021, 39 (8):  802-815.  DOI: 10.3724/SP.J.1123.2020.09004 Abstract ( 246 )   HTML ( 219 )   PDF (4444KB) ( 119 )   Microfluidic paper-based chips have many advantages such as ease of integration, miniaturization, and automation; high throughput; low production cost; easy portability; easy storage and transportation, environmental friendliness, and feasibility of instantaneous detection. These chips are widely used in clinical diagnosis, food quality control, and immunoassays. With the continuous development of microfluidic paper microarrays in recent years, they have also received great attention for environmental contaminant analysis and detection, and research in this field has been intensive, showing excellent prospects for application. This review summarizes the latest research progress in environmental analysis from the perspective of the application of microfluidic paper-based chips, as well as future development trends and challenges. More than 150 papers from the Science Citation Index (SCI) and Chinese core journals are cited in this paper. This review includes the advantages of microfluidic paper-based chips for environmental analysis and detection; the introduction of paper chip fabrication methods, including wax printing, photolithography, dicing, plasma, laser, and inkjet etching; and the introduction of advanced analytical methods based on paper chips, such as electrochemical analysis, fluorescence analysis, colorimetric analysis, surface-enhanced Raman analysis, and integrated sensing methods. The future development trends and prospects of environmental analysis based on microfluidic paper-based chips are also reviewed. Through a rich and comprehensive review of recent related research, it is shown that although microfluidic paper-based chip technology has only been developed for little more than a decade since its introduction, this technology has seen rapid development in environmental analysis-related research and has yielded rich results. The hydrophilic and porous nature of cellulose in paper as a chip substrate allows the passive transport of liquids without an external power source. The diversity of available microfluidic paper-based chip fabrication and analysis methods allows flexible selection and matching according to different environmental conditions and detection requirements, so that the best detection results can be obtained. Moreover, microfluidic paper chips as detection platforms show good biocompatibility in the analysis and detection of environmental pollutants, enabling the analysis of more types of pollutants. The used paper is biodegradable and can be directly disposed of as ordinary garbage after appropriate degradation treatment; thus it is environmentally friendly and does not impact the health of the operators. In addition, the low production cost and simple operation of the paper chip design study make it possible to fabricate low-cost, portable, and practical analytical equipment, which is important for rapid testing of the conventional environment. However, there are some inherent disadvantages: the mechanical strength of the paper is not sufficiently high to resist deformation; degree of fluid control is difficult to achieve the desired effect, and the sample flow may be lost due to leakage; multiple contaminants may interfere with one another when analyzed in parallel; there are difficulties in commercial mass production. However, these problems also point to the direction for the research and development of microfluidic paper-based chips in the field of environmental testing. With continuous advances in manufacturing and analysis technologies, microfluidic paper-based chips are expected to play a more prominent role in future environmental analysis.

Select

Application of carbon dots in analysis and detection of antibiotics CHAI Peijun, SONG Zhihua, LIU Wanhui, XUE Junping, WANG Shuo, LIU Jinqiu, LI Jinhua 2021, 39 (8):  816-826.  DOI: 10.3724/SP.J.1123.2021.04022 Abstract ( 202 )   HTML ( 198 )   PDF (2522KB) ( 99 )   Antibiotics have been overused in recent years because of their remarkable curative effect, but this has led to considerable environmental pollution. Therefore, the development of approaches aimed at the effective detection and control of the antibiotics is vital for protecting the environment and human health. Many conventional strategies (such as high-performance liquid chromatography (HPLC), gas chromatography (GC), high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)) are currently in use for the detection of antibiotics. These strategies have aroused a great deal of interest because of their outstanding features of high efficiency and speed, good reproducibility, automation, etc. However, various problems such as tedious sample pretreatment, low detection sensitivity, and high cost must be overcome for the effective detection of antibiotics in environmental samples. Consequently, it is of great significance to improve the detection sensitivity of antibiotics. The development of new materials combined with the existing detection technology has great potential to improve the detection results for antibiotics. Carbon dots (CDs) are a new class of nanomaterials with particle sizes in the range of 0-10 nm. In addition, CDs have desirable properties such as small particle effect, excellent electrical properties, unique optical properties, and good biocompatibility. Hence, they have been widely utilized for the detection of antibiotics in environmental samples. In this review, the application of CDs combined with sensors and chromatographic technology for the detection of antibiotics in the last five years are summarized. The development prospects of CD-based materials and their application to the analysis and detection of antibiotics are presented. In this review, many new sensors (CDs combined with molecularly imprinted polymer sensors, aptamer sensors, electrochemiluminescence sensors, fluorescence sensors, and electrochemical sensors) combined with CD-based materials and their use in the detection of antibiotics are summarized. Furthermore, advanced analysis methods such as ratiometric sensor and array sensor methods are reviewed. The novel analysis methods provide a new direction toward the detection of antibiotics by CDs combined with a sensor. Moreover, CD-based chromatographic stationary phases for the separation of antibiotics are also summarized in this manuscript. It is reported that the detection sensitivity for antibiotics can be greatly improved by the combination of CDs and a sensor. Nevertheless, a literature survey reveals that the detection of antibiotics in complex environmental samples is confronted with numerous challenges, including the fabrication of highly sensitive sensors in combination with CDs. Furthermore, the development of novel high-performance materials is of imperative. In addition, it is important to develop new methods for effective data processing. The separation of antibiotics with CDs as the chromatographic stationary phases is in the preliminary stage, and the separation mechanism remains to be clarified. In conclusion, there are still many problems to be overcome when using CDs as novel materials for the detection of antibiotics in environmental samples. Nowadays, CD-based materials are being intensively studied, and various analytical detection technologies are being rapidly developed. In the future, CD-based materials are expected to play an important role in the detection of antibiotics and other environmental pollutants.

Select

Research progress on lyophilization for pretreatment of emerging organic contaminants in environmental samples ZHANG Yiqing, GUO Shanshan, SUN Qian 2021, 39 (8):  827-834.  DOI: 10.3724/SP.J.1123.2021.02034 Abstract ( 221 )   HTML ( 199 )   PDF (1019KB) ( 163 )   With rapid urbanization, increasing amounts of chemicals are being used in our daily life. Emerging organic contaminants are a large class of chemicals that are widely detected in the environment. They include pharmaceuticals and personal care products, pesticides, perfluorinated compounds, and endocrine-disrupting compounds. Recently, many countries have reported the occurrence of emerging organic contaminants. In addition, emerging organic contaminants are frequently detected in various environmental samples, including river and lake water samples. Despite their low concentrations in the environment, emerging organic contaminants are potential risks to humans and wildlife. Because they could lead to endocrine disrupting effects and the occurrence of resistance genes. Thus, the detection of emerging organic contaminants in the environment is imperative for ecological systems and human health. The recent development of analytical techniques has led to the identification of more emerging organic contaminants in the environment. At present, the commonly used chromatographic separation techniques include liquid chromatography and gas chromatography. For the identification and quantitation of emerging organic contaminants, chromatography is usually combined with spectroscopy or mass spectrometry. The concentrations of emerging organic contaminants are not sufficiently high to be detected directly, and the matrix is complex in environmental samples. Emerging organic contaminants also have diverse properties. Thus, environmental samples must be pretreated before detection. Pretreatment includes the concentration and purification of the environmental samples. The commonly used pretreatment methods are ultrasound-assisted extraction, QuEChERS, liquid-liquid extraction, and solid-phase extraction. With the development of pretreatment methods, solid-phase microextraction and stirred-bar adsorption extraction have also become popular. These sample pretreatment methods have many advantages such as good efficiency and effectivity for recycling target compounds. Hence, they are widely used. However, these methods are time-consuming, in addition to requiring expensive consumables and large amounts of organic solvents. Lyophilization is a technique used for product dehydration, preservation, and storage in the agricultural and food industries. It is also occasionally used to simplify the extraction procedure for drug residue analysis. There are three stages of lyophilization: freezing, primary drying, and secondary drying. Lyophilization has many advantages when used for pretreatment, namely, operational simplicity, less consumables, less sample volume, prolonged storage, and minimal sample loss. Lyophilization is thus an alternative method for the pretreatment of emerging organic contaminants in environmental samples. Recently, lyophilization has been applied to the pretreatment of emerging organic contaminants in environmental water samples. In general, a few steps were included during sample analysis. First, the samples were pretreated and frozen before the primary drying stage. After lyophilization, the analytes were extracted using a small amount of organic solvent and dried with nitrogen. Consequently, the elution was reconstructed and detected after dryness and filtration. Many groups of emerging organic contaminants could be recovered, including antibiotics, pesticides, and endocrine-disrupting compounds. The lyophilization could be automated, so that minimal manual intervention was required. By adopting lyophilization, good recoveries and accuracies were achieved. A few cleanup processes were conducted, and a small amount of organic solvent was consumed. Thus, lyophilization is a highly prospective pretreatment method for monitoring emerging organic contaminants, and can be extended to a diverse range of these contaminants. For large-scale and high-frequency sampling campaigns, cheap and convenient pretreatment is urgently needed. In this study, typical emerging organic contaminants are described, along with the universal types of such contaminants and the principles of lyophilization. The application of lyophilization to the detection of emerging organic contaminants in the environment is also introduced. The future of lyophilization is discussed, which provides a reference for emerging contaminant detection in environmental samples.

Select

Advances in solid-phase extraction for bisphenols in environmental samples LIU Hongyuan, JIN Jing, GUO Cuicui, CHEN Jiping, HU Chun 2021, 39 (8):  835-844.  DOI: 10.3724/SP.J.1123.2021.02035 Abstract ( 213 )   HTML ( 203 )   PDF (967KB) ( 127 )   Owing to the strict restrictions on the production and use of bisphenol A (BPA), bisphenol analogs (e. g., bisphenol S and bisphenol F) are gradually coming to use in many fields. BPA and these bisphenol analogs are so-called bisphenols (BPs). BPs as a class of endocrine disrupters are widely distributed in the environment (water, sediments, sludge, and aquatic products). BPs enter the human body through various routes, leading to endocrine disruption, cytotoxicity, genotoxicity, reproductive toxicity, dioxin-like effects, and neurotoxicity. The Canadian government has identified BPs as substances for further scoping/problem formulation. Because of the widespread attention paid to BPs in the environmental field, research is being expanded to cover water, sediment, dust, and biological samples, and other media. Given the significant differences in the complexity and pollution concentration of environmental samples, the development of pretreatment methods that afford high extraction efficiency, good purification selectivity, strong universality, operational simplicity, and high-throughput extraction and purification, are necessary to realize the highly sensitive detection of BPs in environmental media. In recent years, solid-phase extraction (SPE), accelerated solvent extraction (ASE), microwave-assisted extraction (MAE), and dispersion liquid-liquid-microextraction (DLLME) as new pretreatment technologies have gradually replaced the traditional liquid-liquid extraction and Soxhlet extraction. SPE has seen rapid development for the extraction and purification of BPs in various environmental samples, overcoming the bottlenecks related to time, energy, and solvent consumption in traditional methods while extending technical support for the analysis of emerging pollutants. The physicochemical properties, usage, and environmental hazards of typical BPs were briefly reviewed, with emphasis on the application of SPE products, development of new adsorbents, and transformation of the SPE mode. Commercialized SPE products are universally applicable in the field of environmental monitoring, while products suitable for the pretreatment of BPs are limited. The development of new adsorbents mainly focused on their adsorption capacity and selectivity. For example, ordered mesoporous silicon, carbon nanomaterials, metal-organic frameworks, and cyclodextrins have large surface areas, good adsorption performance, and regular pore structures, which improve the adsorption capacity of BPs. Molecularly imprinted polymers (MIPs) and mixed-mode ion-exchange polymers are mainly used to improve the selectivity of BPs in the purification process. In addition, MIPs have high chemical, mechanical, and thermal stabilities, which ensures their widespread application in the extraction, preconcentration, and separation of BPs. A variety of new SPE adsorbents can partially meet the diverse needs for detection. There is a consensus that the current challenges in analytical chemistry include the determination of contaminants at low concentration levels, but at the same time, more efficient and environment-friendly methodologies are required. With the introduction of high-sensitivity instruments in the market, the SPE model is seeing gradual development in terms of miniaturization, automation, and simplification. This in turn has minimized solvent consumption, analysis time, and labor cost, resulting in more efficient and affordable analytical methods such as QuEChERS, solid-phase microextraction (SPME), and magnetic solid-phase extraction (MSPE) to adapt to the new development scenario.

Select

Recent advances in chemical derivatization-based chromatography-mass spectrometry methods for analysis of aldehyde biomarkers ZHU Shuyun, ZHAO Xian-En, LIU Huwei 2021, 39 (8):  845-854.  DOI: 10.3724/SP.J.1123.2021.02023 Abstract ( 457 )   HTML ( 205 )   PDF (4080KB) ( 194 )   Human exposure to chemical pollutants in the environment can cause a variety of diseases, including cancer, diabetes, cardiovascular disease, and neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease, etc.). Exogenous and environmental pollutant exposure-induced endogenous aldehydes are highly reactive electrophilic compounds that can form covalently modified products with a variety of important biological molecules in the human body, thus inducing toxic effects. Exposome research has become a hotspot since it was first proposed in 2005. Exposure studies can map the complex relationships between biomarkers and disease risk. Therefore, the measurable and characteristic changes of all biomarkers together constitute a key basis for exposome research. Aldehydes are among the main components of chemical exposure. Because of the physical and chemical properties of aldehydes and the existence of multiple matrix interferences in the samples, it is particularly difficult to analyze and characterize them. The analysis and detection methods for aldehydes mainly include sensing analysis, electrochemical methods, fluorescence imaging, chromatography, mass spectrometry (MS), and chromatography-MS. Analytical techniques based on gas chromatography-MS (GC-MS) and liquid chromatography-MS (LC-MS) have emerged as the main methods for chemical exposome research. Chemical derivatization, especially stable isotope labeling derivatization (also known as chemical isotope labeling) combined with LC-MS analytical techniques, can help circumvent the problems encountered in targeted and non-targeted metabolome and exposome analysis. The combination of chemical derivatization with chromatography-MS is one of the most important solutions for the accurate analysis of aldehydes in complex samples. Over the past five years, the development and application of chromatography-MS analytical methods based on chemical derivatization have become key topics in aldehyde analysis. This paper summarizes and reviews the latest progress in GC-MS and LC-MS methods based on chemical derivatization (2015-2020). The review focuses on analytical method development for aldehyde exposure biomarkers in bio-matrices (blood, urine, saliva, biological tissue, etc.). Various derivatization reagents for labeling small-molecule aldehydes, qualitative/quantitative analytical methods and their application value, advantages/disadvantages of different analytical methods for aldehyde exposure biomarkers, and future development trends are also included. The manuscript contents may aid the integrated development of exposome, metabolomics, and lipidomics, as well as research on the environment, ecology, and health. To clarify the complex actions of exogenous and endogenous aldehydes in physiological and pathological events, it is necessary to improve the analysis and characterization techniques and tools for studying the “aldehydome.” With the development and application of sophisticated mass spectrometers, advances in high-performance chromatographic separation and bioinformatics, and advent of single-cell analysis and MS imaging, future aldehyde exposome analytical methods will have higher sensitivity and throughput. This in turn would be more useful for screening and identifying unknown aldehyde compounds and discovering new exposome biomarkers.

Select

Application of non-stationary phase separation hyphenated with inductively coupled plasma mass spectrometry in the analysis of trace metal-containing nanoparticles in the environment JIANG Haowen, LI Jian, TAN Zhiqiang, GUO Yingying, LIU Yanwei, HU Ligang, YIN Yongguang, CAI Yong, JIANG Guibin 2021, 39 (8):  855-869.  DOI: 10.3724/SP.J.1123.2020.12016 Abstract ( 149 )   HTML ( 24 )   PDF (3293KB) ( 90 )   Engineered metal-containing nanoparticles (MCNs), which have unique physical and chemical properties, are widely used in various fields such as medicine, pharmaceuticals, and microelectronics as well as in daily supplies. These MCNs are inevitably released into the environment during production and use, thus posing a threat to bacterial communities, animals, plants, and human health. There are also abundant natural MCNs in the environment, which play an important role in the environmental cycle of metals. The shape, size, and surface properties of MCNs have a significant impact on their migration, chemical and physical transformation, and biological intake in the environment. Therefore, the analysis and detection of MCNs in the environment should be aimed not only at quantifying their concentration and chemical composition, but also at determining their shape, particle size, and surface charge. In addition, for the detection of MCNs in the environment, challenges due to their low concentrations and the interference from complex environmental matrices must be overcome. A single detection technique is often insufficient for the analysis and detection of MCNs in a complex environment matrix. Therefore, the development of an effective and reliable online hyphenated technique is urgently needed for the separation and detection of MCNs in the environment. Such online hyphenated techniques should be able to eliminate the interference by complex matrices, improve the particle size detection range, and reduce the element detection limit. The online hyphenation of stationary phase-based separation techniques such as liquid chromatography and gel electrophoresis with inductively coupled plasma-mass spectrometry (ICP-MS) can effectively separate MCNs according to their particle size, with low element detection limits. However, these stationary phase-based separation techniques have a shortcoming of the adsorption of nanoparticles on the stationary phase, which leads to blockage of separation channels and low recoveries of nanoparticles. The online hyphenation of a non-stationary phase separation technique with ICP-MS also shows strong nanoparticle separation ability and low element detection limits, so that the problem of colloid blockage in stationary phase-based separation can be resolved. This method is very promising for the rapid and accurate characterization of the particle size distribution and chemical composition of MCNs. However, it cannot provide information about the nanoparticle number concentration of MCNs and the elemental content of a single MCN. In complex environmental samples, pure MCNs cannot be effectively distinguished from MCNs with environmental corona having different thicknesses or pure MCNs adsorbed on/hetero-agglomerated with inorganic/organic colloids. Online coupling single-particle ICP-MS (SP-ICP-MS), an emerging particle detection technique with non-stationary phase separation, can effectively help overcome the above shortcomings. This method can provide information on the hydrodynamic diameter, metal mass-derived diameter, total number concentration, size-dependent number, and size-dependent mass concentration of MCNs. Therefore, it enables comprehensive characterization of MCNs based on a variety of three-dimensional contour plot chromatograms. This review summarizes the separation mechanisms and applicable detectors for three commonly used non-stationary phase separation techniques: hydrodynamic chromatography (HDC), capillary electrophoresis (CE), and field-flow fractionation (FFF). In addition, it focuses on the characteristics and applications of online-coupling non-stationary phase separation with ICP-MS and SP-ICP-MS. Regarding FFF, this review focuses on the separation techniques that are suitable for online coupling with ICP-MS, such as sedimentation FFF and flow FFF (symmetrical flow FFF, asymmetrical flow FFF, and hollow fiber flow FFF). In addition, the characteristics of the online hyphenation of three non-stationary phase separations, HDC, CE, and flow FFF, with ICP-MS are compared, including the separation mechanism, sample volume, analytical time, detection sensitivity, size range, size resolution, recovery, reproducibility, and capability for ion analysis. Finally, this review proposes the prospects for future development of the online hyphenation of non-stationary phase separation techniques with ICP-MS and SP-ICP-MS.

Articles

Select

Adsorption mechanism of typical monohydroxyphenanthrene on polyvinyl chloride microplastics BAO Zhenzong, CHEN Zhifeng, QI Zenghua, WANG Guangzhao, CAI Zongwei 2021, 39 (8):  870-877.  DOI: 10.3724/SP.J.1123.2020.09005 Abstract ( 139 )   HTML ( 38 )   PDF (2822KB) ( 90 )   To enrich data related to the interaction mechanism between microplastics and organic pollutants, in this study, 3-hydroxy-phenanthrene (3-OHP, C14H10O), a phenanthrene derivative, was selected as a representative pollutant, and polyvinyl chloride (PVC) microplastics were chosen as the research objects. We investigated the adsorption behavior of 3-OHP on PVC microplastics in aqueous solutions and explored the adsorption mechanism in detail. The PVC microplastics were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The standard curves of the ultraviolet (UV) absorption spectrum of the target pollutant were obtained using a UV spectrophotometer. The fitting coefficient values of all standard curves were higher than 0.99 (R2>0.99). To ensure the accuracy of the UV absorption spectrum, the pollutant concentration gradient was set according to the absorbance (Abs) values, which were higher than 0.438. The measured concentrations were calculated using a standard curve equation. The adsorption mechanism of 3-OHP on PVC microplastics in an aqueous solution was studied by combining adsorption models (adsorption kinetics model, adsorption isotherm model, and adsorption thermodynamics model) and density functional theory (DFT) calculations. The results are as follows: (1) From the adsorption kinetics experiment, the pseudo-second-order kinetic model had the best fitting degree, and the fitting coefficient of adsorption kinetics was 0.998 (R2=0.998). Hence, 3-OHP adsorption on PVC microplastics may be attributed to surface adsorption and external liquid film diffusion; the equilibrium adsorption amount was 36.866 μg/g after 24 h. (2) The adsorption isotherm experiment showed that the Langmuir and Freundlich isotherm models were more suitable for describing the adsorption mechanism of 3-OHP adsorption on PVC microplastics because of the satisfactory fitting coefficient (R 2=0.956 and 0.907), suggesting that the adsorption mode was mainly single-layer adsorption with a small amount of multilayer adsorption. The maximum adsorption amount of 3-OHP adsorption on PVC microplastics was 408 μg/g; (3) the adsorption thermodynamics results showed that the adsorption efficiency of 3-OHP adsorption on PVC microplastics decreased with increasing temperature, indicating that the adsorption of 3-OHP on PVC microplastics was a spontaneous and exothermic adsorption process; (4) the salinity experiment results showed that salinity had little effect on the adsorption efficiency of 3-OHP on PVC microplastics; (5) DFT calculations showed that PVC had a relatively low binding energy to 3-OHP. Therefore, we suggest that the main adsorption mechanism of 3-OHP on PVC microplastics may be the hydrophobic effect; weak hydrogen bonding, halogen bonding, and π-π conjugate action could also play a role in 3-OHP adsorption on PVC. These results reveal the interaction mechanism between PVC microplastics and organic chemicals, and enhance our understanding of the environmental behavior of PVC microplastics in aqueous solutions. To serve as a reference in scientific evaluations of the environmental impact of microplastics, future studies should focus on obtaining toxicological data for the microplastics.

Select

Simultaneous determination of 30 antibiotics in soil by ultra-high performance liquid chromatography-tandem mass spectrometry HU Yu, ZHU Qingqing, HU Ligang, LIAO Chunyang 2021, 39 (8):  878-888.  DOI: 10.3724/SP.J.1123.2021.02019 Abstract ( 343 )   HTML ( 83 )   PDF (2941KB) ( 222 )   The complexity of the soil matrix, as well as the wide spectrum and trace levels of antibiotic residues in soil, make highly sensitive instrumental methods, efficient purification and enrichment methods, and simultaneous determination of multiple antibiotics key and challenging aspects in the analysis of antibiotics in soil. In this study, a solid phase extraction-ultra-high performance liquid chromatography-tandem mass spectrometry (SPE-UHPLC-MS/MS) method was developed for the simultaneous determination of 30 antibiotics (grouped into seven categories: sulfonamides, fluoroquinolones, tetracyclines, macrolides, β-lactams, amphenicols, and lincosamides) in soil samples. In the UHPLC-MS/MS experiment, florfenicol and chloramphenicol were analyzed in the negative ionization multiple-reaction monitoring (MRM) mode, and the other 28 target analytes were analyzed in the positive MRM mode. Sensitive MS conditions were realized by optimizing the instrumental parameters such as collision energy and declustering potential. The effects of the injection solvent (proportion of methanol to water) and mobile phase (types and compositions of the solvents) on the shape and intensity of the chromatographic peaks were studied. The optimized UHPLC conditions were as follows: injection solvent, 10%(v/v) methanol aqueous solution; chromatographic column, BEH-C18 column; mobile phase, methanol and water both containing 0.1%(v/v) formic acid; flow rate, 0.4 mL/min; sample injection volume, 5.0 μL. The effects of the extraction solution (the types and compositions of solvents) and clean-up processes (pH of the loading solution, as well as the types and compositions of the rinse solution and elution solvent) on the method performance were investigated. The acetonitrile/Na2EDTA-McIlvaine buffer showed better extraction efficiency for fluoroquinolones than did the methanol/Na2EDTA-McIlvaine buffer. Improved recoveries of sulfonamides, macrolides, tetracyclines, and β-lactams were observed when the pH of the loading solution was set to 8.0. The recoveries of sulfadiazine and amoxicillin increased with a decrease in the proportion of methanol to water for the rinse solution. Compared to individual methanol or acetonitrile, the methanol-acetonitrile (1∶1, v/v) mixture showed better elution efficiency for the target analytes. The optimized pretreatment conditions were determined as follows: the soil sample was spiked with mixed internal standards, and then extracted with 10 mL of acetonitrile/Na2EDTA-McIlvaine buffer (1∶1, v/v) by shaking for 30 min and ultrasonication for 15 min. The extraction was repeated three times. The sample extract was adjusted to pH 8.0 and loaded onto an Oasis HLB cartridge for purification. The cartridge was rinsed with 10 mL of water to remove impurities and eluted with 10 mL of methanol-acetonitrile (1∶1, v/v). Quantitative analysis was conducted using the isotope internal standard method. The method limits of detection and quantification were in the range of 0.013-1.21 and 0.043-4.04 μg/kg, respectively. The correlation coefficients of the calibration curve were 0.992-1.00, suggesting good linearity of the method. At three spiked levels (20, 100, and 200 μg/kg), the average recoveries of most target antibiotics were 44.8% to 164%, and the relative standard deviations were 0.700% to 14.8%. The method was successfully applied to the analysis of the 30 antibiotics in six soil samples. Seventeen antibiotics were detected in the soil samples, and the total contents of the antibiotics in each sample ranged from 73.4 to 184 μg/kg. Twelve antibiotics with a detection frequency of 100% included roxithromycin, clarithromycin, ciprofloxacin, norfloxacin, enrofloxacin, ofloxacin, fleroxacin, lomefloxacin, oxytetracycline, doxycycline, tetracycline, and penicillin G. Ciprofloxacin and norfloxacin were the predominant antibiotics in the soils, with contents in the range of 13.7-32.1 and 15.6-43.6 μg/kg, respectively. The developed method is simple, rapid, and solvent-saving, and it shows promise for use in the simultaneous determination of trace levels of the 30 antibiotics in soil.

Select

Determination of domoic acid in seawater by solid phase extraction-liquid chromatography-tandem mass spectrometry WANG Jiuming, CHEN Junhui, YANG Jianbo, HE Xiuping, WANG Yuning, WANG Baodong 2021, 39 (8):  889-895.  DOI: 10.3724/SP.J.1123.2021.02026 Abstract ( 195 )   HTML ( 35 )   PDF (1123KB) ( 99 )   Domoic acid (DA) can poison or even be fatal to marine mammals, and poses a potential risk to human health via transmission through the food chain. The level of DA in seawater will affect the safety of seafood. Therefore, a powerful method for the detection of DA in seawater, especially in the coastal mariculture zone, is needed. In order to identify different concentration levels of DA in real seawater, in this study, a method was established for the determination of trace DA in seawater by SPE-LC-MS/MS. First, the LC-MS/MS instrument and sample pretreatment conditions were optimized. Subsequently, DA was separated on a 5 TC-C18 (2) analytical column (150 mm×4.6 mm, 5 μm), and multiple reaction monitoring (MRM) was conducted in the positive electrospray ionization mode. For off-line SPE, the HLB cartridge could enrich DA in seawater. The best enrichment of DA was obtained after adding 0.32 mL formic acid to an 80.0 mL seawater sample. Four on-line SPE columns from Agilent, namely, 5 TC-C18(2) (12.5 mm×4.6 mm, 5 μm), Zorbax Eclipse Plus-C18 (12.5 mm×2.1 mm, 5 μm), Zorbax Eclipse XDB-C8 (12.5 mm×2.1 mm, 5 μm), and PLRP-S (12.5 mm×2.1 mm, 15-20 μm), were tested to determine their suitability to trap DA from seawater samples. The 5 TC-C18 (2) column offered the best retention ability and good peak shape of DA, and was selected as the on-line SPE column. Validation was then performed to assess the sensitivity, linearity, matrix effects (MEs), recoveries, and precisions of the proposed method. After simple treatment of the seawater samples by filtration and acidification, 0.6 mL of the seawater sample was injected directly for on-line SPE-LC-MS/MS. The linearity was good, and ranged from 10.0 to 500.0 ng/L (correlation coefficient R2=0.9992). The limit of detection (LOD) and limit of quantification (LOQ) of DA were 4.0 and 10.0 ng/L, respectively, with good recovery (≥81.0%) and precision (RSDs≤4.2%) at three spiked levels in the blank seawater samples. After the DA in the 80.0 mL seawater sample was enriched by off-line SPE, a 0.6 mL sample was injected for on-line SPE-LC-MS/MS. The DA in the spiked blank seawater sample showed a good linear relationship in the range of 0.3-50.0 ng/L (R2=0.9990). The LOD and LOQ were 0.1 and 0.3 ng/L, respectively. The recoveries of DA at low, medium, and high spiked levels in the blank seawater samples were all ≥69.2%, and the RSDs were ≤4.4%. The MEs of DA with both methods were 18.3% and 13.7%, respectively, indicating that the ME was mild enough to be negligible. In summary, the proposed method is simple, sensitive, robust, and powerful for the detection of DA in inshore and offshore seawater.

Select

Determination of seven phenoxy acid herbicides in water by dispersive solid phase extraction-ultra performance liquid chromatography-tandem mass spectrometry based on cationic metal-organic framework mixed matrix membrane JI Xuefeng, LI Shuang, WU Gege, ZHAO Lin, MA Jiping 2021, 39 (8):  896-904.  DOI: 10.3724/SP.J.1123.2021.01006 Abstract ( 167 )   HTML ( 33 )   PDF (3685KB) ( 114 )   Phenoxy acid herbicides are widely used because of their excellent efficiency and low cost. However, owing to their strong polarity and water solubility, these herbicides do not degrade easily in a water environment and persist for a long time in water bodies. These herbicides readily enter water bodies via surface runoff, infiltration, and other migration routes, thus affecting water quality safety. Therefore, it is of great significance to establish a sensitive and simple method for the quantitative analysis of phenoxy acid herbicides in environmental water. Given the low concentration of such contaminants in environmental water, appropriate detection methods are important. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has high sensitivity and accuracy, thus being well suited for the phenoxy acid herbicides analysis. Sample preparation techniques are also important for the extraction and enrichment of contaminants in environmental water. Dispersive solid phase extraction (DSPE) has attracted considerable attention owing to its low cost, ease of operation, and low solvent consumption. In general, the selectivity and efficiency of solid phase extraction are largely dependent on the characteristics of the solid adsorbent materials. Ionic metal-organic frameworks (iMOFs) have excellent ion-exchange properties and show selective absorptivity to ionic compounds. In this work, a metal-organic framework (MOF) MIL-101-NH2 was synthesized by a facile hydrothermal method. Then, a cationic MOF mixed matrix membrane (MMM) was fabricated by soaking the MOFs in a polyvinylidene fluoride (PVDF) solution and further functionalization with quaternary amine groups. A method was developed for the determination of seven phenoxy acid herbicides in water by UPLC-MS/MS based on DSPE. The prepared material was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy to determine its functional groups and morphology. The results showed that there were quaternary amine groups in the material, and that the functionalization did not have any obvious effect on the chemical and crystal structures of MIL-101-NH2. The prepared MIL-101-$NMe_{3}^{+}$-PVDF MMM was used as an adsorbent for DSPE to enrich the seven phenoxy acid herbicides in water. It is well known that the key factors influencing extraction efficiency are the adsorption and elution conditions. To establish the optimum extraction conditions, the influence of some important factors, including the adsorbent amount, sample pH, extraction time, elution solvent, elution volume, and elution time, was investigated in detail. Gradient elution was carried out with 0.01% formic acid aqueous solution and acetonitrile as the mobile phase. The target analytes were separated on an ACQUITY UPLC BEH C18 column (100 mm×2.1 mm, 1.7 μm), and multiple reaction monitoring (MRM) was conducted in the negative electrospray ionization mode. The external standard method was used for quantitative analysis. The established method was verified in terms of the linear ranges, limits of detection (LODs), limits of quantification (LOQs), recoveries, and precision. Under the optimal conditions, the seven phenoxy acid herbicides showed good linear relationships in their respective concentration ranges, and the correlation coefficients were all higher than 0.997. The LODs and LOQs were 0.00010-0.00090 μg/L and 0.00033-0.00300 μg/L, respectively. The recoveries were tested at three spiked levels of 0.005, 0.05, and 0.2 μg/L. The average recoveries of the seven compounds were in the range of 80% to 102%. The intra-day and inter-day relative standard deviations were within 1.4% to 9.4% and 4.2% to 12.6%, respectively. The established method was applied to the analysis of the phenoxy acid herbicides in tap water and reservoir water. Three levels of spiked samples were adopted to investigate the accuracy of the method. The results demonstrated that our method is applicable to the detection of trace phenoxy acid herbicides in water samples. In summary, this method has the advantages of simplicity, rapidity, and sensitivity, and it is suitable for the detection of the seven phenoxy acid herbicides in environmental water.

Select

Simultaneous determination of saturated and aromatic hydrocarbons in soil by on-line high performance liquid chromatography-gas chromatography LIU Lingling, LI Bingning, WU Yanwen 2021, 39 (8):  905-912.  DOI: 10.3724/SP.J.1123.2021.02011 Abstract ( 172 )   HTML ( 37 )   PDF (1427KB) ( 92 )   To strengthen regulation for mitigating the risk posed by petroleum contaminants in soil, the Ministry of Ecology and Environment of the People’s Republic of China has classified petroleum hydrocarbons as a key monitoring item for regulatory contamination monitoring. Petroleum is principally derived from petroleum and synthetic fuels, which contain an extremely high content of hydrocarbon compounds that have varied boiling points. These compounds are chemically classified primarily as saturated and aromatic. Aromatic hydrocarbons are typically highly alkylated monocyclic, bicyclic, and polycyclic, which are more toxic to human and animal life than saturated hydrocarbons. Because of the significant toxicological differences among the various hydrocarbons, it is difficult to accurately assess their environmental toxicity by only determining the total content of petroleum in soil. However, there are no analytical methods for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil according to Chinese standards. In this study, extraction and purification procedures were completely optimized depending on the matrix of the soil samples. The advanced analytical technique of on-line high performance liquid chromatography-gas chromatography (HPLC-GC) was performed after sample preparation for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil. For the extraction, n-hexane/ethanol (1∶1, v/v) was chosen as the extraction solvent. The ratio of solid sample (soil) to the solvent was chosen as 1∶4, and extraction was performed once at room temperature, for 1 h. Water was then added and mixed to remove ethanol from the extracts, and the upper n-hexane layer was separated; thus, the petroleum hydrocarbons in the samples were completely extracted. However, the oils and fats in the matrix of the soil sample were also simultaneously extracted. Because of the limited retention capacity of the HPLC column, the presence of oils, fats, and other interferents would affect the subsequent determination of saturated hydrocarbons and aromatic hydrocarbons. Therefore, an additional purification step is required before sample injection into the HPLC-GC equipment. In this study, purification was performed using a lab-made silica gel column, which is commonly used for the determination of saturated hydrocarbons and aromatic hydrocarbons in food. The purification column was conditioned and eluted with an 8∶2 ratio (v/v) of n-hexane to dichloromethane after sample loading. Subsequently, the eluent was concentrated and injected into the HPLC-GC equipment for analysis. The flame ionization detector (FID) is ideal for petroleum hydrocarbons quantification because of its nearly identical responses to all hydrocarbons; hence, with the FID, reference standards are not required for quantification, and internal standards are typically used for quantifying the total hydrocarbon content. In this study, cyclohexylcyclohexane (Cycy) and 2-methylnaphthalene (2-MN) were used as internal standards for determining the saturated and aromatic hydrocarbons, respectively. The limit of quantification (LOQ) of this proposed method was 0.4 mg/kg. Moreover, the suitability of the method was verified by comparing the obtained content against the soil petroleum hydrocarbon standard (SQC-116); the measured value was found to be within the credible interval provided by the standard. The relative error (RE) was 10.6% with a relative standard deviation (RSD) of 1.4%, which indicates that the proposed method is accurate and reliable, and the precision meets analytical requirements. Finally, the method was applied to the determination of hydrocarbons in five soil samples from the Beijing area. Saturated hydrocarbons (C10-C40) were detected in all five samples, with contents ranging from 3.3 to 32.1 mg/kg, while aromatic hydrocarbons (C10-C40) were detected in four samples, with contents ranging from 0.8 to 4.3 mg/kg. HPLC-GC combines the high selectivity of HPLC with the high separation efficiency of GC, and as demonstrated in this study, can be used for the simultaneous determination of saturated and aromatic hydrocarbons in soil. The source of hydrocarbon contamination can also be preliminarily identified by chromatographic analysis.

Select

Determination of cyanogen chloride in organic and water matrices by gas chromatography-mass spectrometry based on thiol derivatization LI Xiaosen, WU Jina, XIA Junmei, YUAN Ling, YANG Yang 2021, 39 (8):  913-920.  DOI: 10.3724/SP.J.1123.2020.12004 Abstract ( 155 )   HTML ( 30 )   PDF (938KB) ( 80 )   Cyanogen chloride (ClCN) has been widely used in industrial production. ClCN is also listed in the Schedule of the Chemical Weapons Convention (CWC). The use of traditional colorimetric analysis or gas chromatography for the detection of ClCN has been characterized by low efficiency and poor sensitivity. In this study, a method was established for the qualitative analysis and quantitative detection of ClCN in organic and water matrices by gas chromatography-mass spectrometry (GC-MS) based on thiol derivatization. 1-Butylthiol was selected as the optimal derivatization reagent. The optimal temperature for thiol derivatization in the organic matrices was 40 ℃ and the reaction time was 10 min. The pH for derivatization was approximately 9. The ClCN in the organic matrices was directly analyzed by GC-MS after derivatization. The conditions of ClCN derivatization in the water matrices were the same as those in the organic matrices. After the derivatization of ClCN, headspace-solid phase microextraction (HS-SPME) was employed during sample preparation for water matrices. Different temperatures for HS-SPME were explored, and the optimal temperature was found to be 55 ℃. The product of thiol derivatization was confirmed as butyl thiocyanate. The main fragmentation patterns and mass spectrometric cleavage pathway were investigated by GC-MS/MS. The quantitative determination of ClCN in organic and water matrices was conducted via the internal standard and external standard methods, respectively. ClCN showed good linearity in the corresponding ranges in the organic and water matrices. The correlation coefficients for both matrices were greater than 0.99. The linearities of ClCN in the organic and water matrices were in the range of 20-2000 μg/L and 20-1200 μg/L, respectively. An organic sample and water samples from different substrates were selected to verify the accuracy and precision of the method at three spiked levels. The average spiked recoveries of ClCN in the organic sample and water samples were 87.3%-98.8% and 97.6%-102.2%, respectively. The corresponding relative standard deviations (RSDs, n=6) were 2.1%-4.7% and 2.8%-4.2%. The derivatization method established in this study showed good reaction specificity. The method was successfully applied in the analysis of samples obtained from the Organisation for the Prohibition of Chemical Weapons (OPCW). The method established in this study for the detection of ClCN showed high sensitivity and precision, and could aid in the analysis and detection of ClCN in the environment.

Technical Notes

Select

Multimaterial 3D-printed contactless conductivity/laser-induced fluorescence dual-detection cell for capillary electrophoresis ZHANG Piwang, YANG Liye, LIU Qiang, LU Shangui, LIANG Ying, ZHANG Min 2021, 39 (8):  921-926.  DOI: 10.3724/SP.J.1123.2021.02021 Abstract ( 207 )   HTML ( 31 )   PDF (1440KB) ( 111 )   Dual detection, which simultaneously employs two complementary detection methods, is a useful approach to enhance the selectivity and sensitivity of capillary electrophoresis (CE). Through dual detection, multiple classes of analytes with different structural and chemical characteristics can be sensitively detected using a single CE method. In addition, the comigrating peaks can be distinguished by comparing the signal outputs of two detectors with different selectivities. Typically, dual detection is achieved by coupling two detectors in series along a capillary. However, in this approach, it is inconvenient to evaluate the signal outputs of the two detectors. The two detectors present differences in their corresponding effective capillary lengths and dead volumes of the detection cell. Therefore, detectors that combine two or three detection methods in a single detection point are proposed to address this issue. In this work, to fabricate a combined detector in a simple and low-cost manner, multimaterial 3D printing technology is employed. A two-in-one detection cell that combines capacitively coupled contactless conductivity detection (C4D) and confocal laser-induced fluorescence (LIF) detection was fabricated by 3D printing functional materials. In 3D printing, conductive composite polylactic acid (PLA, Proto-pasta) filaments and normal nonconductive PLA filaments were employed. The conductive material was used to build a C4D shielding layer that was electrically grounded. The nonconductive PLA was used as an electrical insulator placed between the shielding layer and C4D electrodes, which were two stainless-steel tubes (0.4 mm i.d. and 5 mm length). To embed the electrodes into the nonconductive material, a “print-pause-print” approach was applied. After building two chambers for housing electrodes using nonconductive PLA, the 3D printing was paused, following which the two electrodes were manually installed. Printing was then resumed, and the remaining part was built. The two electrodes were 2 mm apart, and the gap between them was filled with a conductive material for shielding to eliminate stray capacitance. A through-hole (1 mm i.d.) was placed between the middle conductive shielding layer for LIF detection. The size of the detection cell was 60 mm×29 mm×7.2 mm. The cell was screwed onto an XYZ stage to precisely align the light path of LIF detection, which was realized using a TriSep TM-2100LIF detector equipped with a 473 nm laser. C4D detection was achieved using a TraceDec detector equipped with a ChipCE adaptor. The two-in-one detector was coupled with a lab-made CE system that had a flow-through injection interface. Use of the detection cell allows the simultaneous detection of inorganic cations and fluorescein isothiocyanate (FITC)-labeled amino acids. The C4D excitation frequency and buffer concentration were then optimized. A mixture of 10 mmol/L 3-(N-morpholino)propanesulfonic acid (MOPS) and 10 mmol/L bis(2-hydroxyethyl)amino-tris(hydroxymethyl)methane (Bis-Tris) was selected as the background electrolyte as a compromise of C4D signal-to-noise ratio (S/N) and separation efficiencies of amino acids. The C4D excitation frequency was set to 77 kHz with S/N=233±8 for 200 μmol/L Na +. The baseline separation of Na+, K+, Li+, FITC, fluorescein, histidine (His), lysine (Lys), tryptophan (Trp), phenylalanine (Phe), alanine (Ala), and glycine (Gly) was achieved with a 25 μm i.d.×365 μm o.d.×45 cm (35 cm effective length) capillary and -10 kV separation voltage. The limits of detection (LODs) of C 4D for Na+, K+, and Li+were 2.2, 2.0, and 2.6 μmol/L, respectively. The LODs of LIF for fluorescein and FITC were 7.6 and 1.7 nmol/L, respectively. The relative standard deviations (RSDs) of the two detection methods were within the range of 0.3%-4.5% (n=3). The r 2 of the calibration curves was ≥0.9904. Thus, 3D printing technology is a simple and low-cost approach to implement complex designs, including those that are difficult to fabricate by traditional “workshop” technologies.