Review of recent advances in the preparation of organic polymer monoliths for liquid chromatography of large molecules

In recent years the use of monolithic polymers in separation science has greatly increased due to the advantages these materials present over particle-based stationary phases, such as their relative ease of preparation and good permeability. For these reasons, these materials present high potential as stationary phases for the separation and purification of large molecules such as proteins, peptides, nucleic acids and cells. An example of this is the wide range of commercial available polymer-based monolithic columns now present in the market.     

Application of monolithic (continuous bed) chromatographic columns in phytochemical analysis

One and a half decade passed since the pioneering work on synthesis and application of non-particulate monolithic stationary phases for liquid chromatography was published by S. Hjertén et al. [S. Hjertén, J.L. Liao, R. Zhang, J. Chromatogr. 473 (1989) 273]. This technique attracted much interest and effort of the researchers developing chromatographic methods and designing chromatographic stationary phases due to several generic qualities of the monolithic (continuous bed) technique. Advantages include: flexibility of the technique in sense of chemistries and functional compositions of the resultant stationary phases; low separation impedance (ratio of pressure drop and efficiency) of monolithic columns; compatibility with micro and nanoformat separations; low time and labour consumption and cost-efficiency. Not surprisingly, these materials attracted interest from phytochemists as plants constitute a complex matrix. However to date, not many successful studies were published in the area of monolithic materials for solving plant metabolomics problems or substituting common particulate materials with monolithic stationary phases in phytochemical analysis. This paper provides an overview.     

有序介孔材料在分离科学中的应用

在简要介绍有序介孔材料发展的基础上，重点综述了其在分离科学中作为吸附剂和色谱固定相的应用，并指出了其在应用中所存在的一些问题及今后的发展趋势。     

Monolithic stationary phases for fast ion chromatography and capillary electrochromatography of inorganic ions

The focus of this review is on current developments in monolithic stationary phases for the fast analysis of inorganic ions and other small molecules in ion chromatography (IC) and capillary electrochromatography (CEC), concentrating in particular on the properties of organic (polymer) monolithic materials in comparison to inorganic (silica-based) monoliths. The applicability of these materials for fast IC is discussed in the context of recent publications, including the range of synthesis and modification procedures described. While commercial monolithic silica columns already show promising results on current IC instrumentation, polymer-based monolithic stationary phases are currently predominantly used in the capillary format on modified micro-IC systems. However, they are beginning to find application in IC particularly under high pH conditions, with the potential to replace their particle-packed counterparts.     

Development of silica-based stationary phases for high-performance liquid chromatography

Stationary phases are the basis of the development and application of high-performance liquid chromatography (HPLC). In this review we focused on the development of silica-based stationary phases, including the synthesis of silica gel and the application of silica in hydrophilic interaction chromatography (HILIC), reversed-phase liquid chromatography (RPLC), chiral separation chromatography, and ion chromatography. New stationary phases, advances in ionic liquid-modified silica, silica-based core-shell materials, and silica-based monolithic columns for HPLC are introduced separately.     

Characterization of monolithic columns for HPLC

Monolithic stationary phases and columns have rapidly become highly popular separation media for liquid chromatography, in spite of their recent discovery. However, their most important features have not yet been completely clarified. A complete understanding of their performance and of their intrinsic characteristics will require the systematic acquisition of many series of reliable experimental data and their consistent analysis from different points of view. Progress in their design and production requires now that the chromatographic behavior of monolithic columns be studied in close connection with their physico-chemical and structural properties. The main goal of this review is to summarize fundamental information on some physico-chemical and chromatographic characteristics of monolithic stationary phases and columns for RPLC. The material reviewed deals only with silica-based monolithic columns. First, structural information on the porosities and the size of the pores in monolithic columns is reported. Second, results of chromatographic studies that deal with the characterization of monolithic columns are summarized. Third, results of detailed studies made on the adsorption equilibrium and the surface heterogeneity of monolithic stationary phases are presented. Finally, results on the mass transfer kinetics in monolithic columns derived from the applications of the classical random-walk model and of the moment theory to a new model of the monolith are discussed.     

金属有机骨架及其复合材料在分离领域中的应用进展

金属有机骨架（MOFs）是一类由无机金属离子与有机配体自组装形成的新型有机-无机杂化多孔材料,因具有比表面积超高、结构多样、热稳定性良好、孔道尺寸和性质可调等优势,在分离领域表现出重要的应用价值。然而,采用传统方法制备的MOFs多为粒径在微米或亚微米尺度的晶体,且颗粒形貌不规则,因此限制了MOFs在样品前处理和色谱固定相等领域的应用和发展。构建基于MOFs的复合材料是弥补MOFs应用缺陷的一项有效措施,有望在保留MOFs优越的分离特性的同时,引入基体材料的特定性能。该文简要综述了近年来MOFs及其复合材料在吸附、样品前处理和色谱固定相等分离领域中的应用进展,并对MOFs在分离科学中的应用前景做出展望。     

Recent strategies to enhance the performance of polymer monoliths for analytical separations

This review summarizes recent developments made in the incorporation of functional materials into organic polymer monoliths, together with new monolithic forms and formats, which enhance their application as supports and stationary phase materials for sample preparation and chromatographic separations. While polymer monoliths are well‐known supports for the separation of large molecules, recent developments have been made to improve their features for the separation of small molecules. The selectivity and performance of organic polymer monoliths has been improved by the incorporation of different materials, such as metal‐organic frameworks, covalent organic frameworks, or other types of nanostructured materials (carbon nanohorns, nanodiamonds, polyoxometalates, layered double hydroxides, or attapulgite). The surface area of polymer monoliths has been significantly increased by polymer hypercrosslinking, resulting in increased efficiency when applied to the separation of small molecules. In addition, recent exploration of less conventional supports for casting polymer monoliths, including photonic fibres and 3D printed materials, has opened new avenues for the applications of polymer monoliths in the field of separation science. Recent developments made in these topics are covered, focusing on the strategies followed by the authors to prepare the polymer monoliths and the effect of these modifications on the developed analytical applications.     

A Review of Ionic Liquids in Chromatographic and Electromigration Techniques

Although there have been numerous studies on the use of ionic liquids (IL) as solvents for synthesis and catalysis, there are many potential new fields for their application. The number of studies dealing with the use of ILs as additives to the mobile phase in LC and CZE and as a stationary phases in GC is constantly increasing. The main goal of the present paper is to gather together studies concerning the use of ILs in chromatographic techniques. The application of these substances as stationary phases, mobile phase additives and electroosmotic flow modifiers is discussed. Conversely, the application of separation methods in the analysis of ILs is also the subject of this review.     

Recent advances in the preparation and application of monolithic capillary columns in separation science

Novel column technologies involving various materials and efficient reactions have been investigated for the fabrication of monolithic capillary columns in the field of analytical chemistry. In addition to the development of these miniaturized systems, a variety of microscale separation applications have achieved noteworthy results, providing a stepping stone for new types of chromatographic columns with improved efficiency and selectivity. Three novel strategies for the preparation of capillary monoliths, including ionic liquid-based approaches, nanoparticle-based approaches and “click chemistry”, are highlighted in this review. Furthermore, we present the employment of state-of-the-art capillary monolithic stationary phases for enantioseparation, solid-phase microextraction, mixed-mode separation and immobilized enzyme reactors. The review concludes with recommendations for future studies and improvements in this field of research.     

Stationary phases for chromatography prepared by ring opening metathesis polymerization

The chemistry of metathesis polymerization-derived stationary phases is summarized. Since both ring-opening metathesis and 1-alkyne polymerization triggered by well-defined transition metal alkylidenes are living polymerization methods, they allow for the controlled and highly reproducible synthesis of stationary phases in terms of both the nature and total content of the functional group(s) of interest. In addition, the high functionality tolerance of these polymerization techniques allows for creating chromatographic supports with an unprecedented diversity in terms of functional groups that may be introduced. Their applications in various areas of separation science such as SPE, ion-chromatography, RP chromatography, chiral chromatography, and the high-performance liquid chromatographic separation of biomolecules are summarized. Within the context of the latter topic, special attention will be given to metathesis polymerization-derived monolithic supports. Consideration will also be given to those aspects of polymer chemistry that are relevant to the separation performance of these supports.     

Recent development of monolithic stationary phases with emphasis on microscale chromatographic separation

The column technologies play a crucial role in the development of new methods and technologies for the separation of biological samples containing hundreds to thousands compounds. This review focuses on the development of monolithic technology in micro-column formats for biological analysis, especially in capillary liquid chromatography, capillary electrochromatography and microfluidic devices in the past 5 years (2002-2007) since our last review in 2002 on monoliths for HPLC and CEC. The fabrication and functionalization of monoliths were summarized and discussed, with the aim of presenting how monolithic technology has been playing as an attractive tool for improving the power of existing chromatographic separation processes. This review consists of two parts: (i) the recent development in fabrication of monolithic stationary phases from direct synthesis to post-functionalization of the polymer- and silica-based monoliths tailoring the physical/chemical properties of porous monoliths; (ii) the application of monolithic stationary phases for one- and multi-dimensional capillary liquid chromatography, fast separation in capillary electro-driven chromatography, and microfluidic devices.     

Monolithic stationary phases for liquid chromatography and capillary electrochromatography

A monolithic stationary phase is the continuous unitary porous structure prepared by in situ polymerization or consolidation inside the column tubing and, if necessary, the surface is functionalized to convert it into a sorbent with the desired chromatographic binding properties [J. Chromatogr. A 855 (1999) 273]. Monolithic stationary phases have attracted considerable attention in liquid chromatography and capillary electrochromatography in recent years due to their simple preparation procedure, unique properties and excellent performance, especially for separation of biopolymers. This review summarizes the preparation, characterization and applications of the monolithic stationary phases. In addition, the disadvantages and limitations of the monolithic stationary phases are also briefly discussed.     

Application of carbon nanotubes in extraction and chromatographic analysis: A review

Carbon nanotube (CNT), a well-known carbon-based nanomaterial has drawn much attention in many application fields including chemistry in the last few decades. Many researchers and scientists have shown huge interest to improve the extraction methodologies and adopt their applications in combination with chromatography technique. With respect to this, the exceptional applications of CNTs have been introduced as extraction sorbent due to their excellent inborn physical and chemical properties. In particular, CNTs have consistently been used as adsorbents in various techniques including solid-phase micro-extraction, solid-phase extraction, micro dispersive slid phase extraction, magnetic dispersive solid phase extraction, analytes enrichment, sample fractionation and clean-up as well as support for many derivatization reactions. Many research papers have discussed the successful use of CNTs to overcome the limitations of the extraction techniques due to their excellent sorbent capacity. In addition, considering the clear need to make chromatographic technique more successful, the applications of CNTs have been reported in the literatures in details as stationary and pseudo-stationary phases for the separation and extraction of challenging compounds. Because of the higher thermal and chemical stability, CNTs have been anticipated as stationary phase modifier for chromatographic applications to avoid bleeding of the columns and enable the analysis even at very high temperature (1200 °C). In liquid chromatography CNTs have primarily been used in combination with other packing materials (silica) and sometimes incorporated in a porous polymeric monolith. Therefore, the recent utilizations of CNTs as extraction materials and stationary phases have been illustrated in the current review and a table listing the details applications of CNTs in aforementioned field is provided as well. We believe that the review will help researcher to gain vast knowledge about application of carbon nanotubes in the field of separation chemistry.     

Recent development of monolithic materials as matrices in microcolumn separation systems

This review summarizes the development of monolithic materials, including both organic and inorganic polymers, according mainly to the papers published in the past two years. Due to their good permeability, fast mass transfer, high stability, and their ease of modification, such materials have been widely used in microcolumn separation systems, not only as stationary phases for CEC and capillary HPLC, but also as substances for sample concentration and enzyme reactor. All the research results demonstrate that monolithic materials in microseparation systems can be expected to play an increasingly important role in the analysis of complex samples.     

Polymeric monolithic stationary phases for capillary electrochromatography

This review summarizes the contributions of a number of groups working in the rapidly growing area of monolithic columns for capillary electrochromatography (CEC), with a focus on those prepared from synthetic polymers. Monoliths have quickly become a well-established stationary phase format in the field of CEC. The simplicity of their in situ preparation method as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. A wide variety of approaches as well as materials used for the preparation of the monolithic stationary phases are detailed. Their excellent chromatographic performance is demonstrated by numerous separations of different analytes.     

高效液相色谱整体柱在药物分离分析中的应用进展

本文对高效液相整体柱在药物分离分析方面的应用进行了综述.主要介绍了以烷氧基硅烷为主要原料,采用溶胶-凝胶法制备的硅胶整体柱,由于其具有微米级通孔结构和大的比表面积,他们在高效、快速分离小分子物质方面得到广泛地应用.对于聚合物整体柱,主要介绍了包括分子印迹聚合物在内的有机聚合物整体柱在药物分离、生物样品的处理等方面的应用.     

聚多巴胺表面修饰毛细管电色谱的研究进展

毛细管电泳(CE)具有分离时间短、分离效率高、样品消耗量低等优点,在分离分析领域有着重要应用。原始的未修饰熔融石英毛细管只能提供阴极流向的电渗流和单一的电泳分离机制,分离性能有限,重复性较差,不能满足各类复杂样品体系尤其是中性和手性样品的分离需求。因此,有必要在CE中引入各类毛细管修饰策略,以拓展其实际应用潜力。贻贝仿生聚多巴胺(PDA)及其衍生材料因其简便易行的制备过程、优异的表面黏附性、良好的生物相容性、较强的二次反应活性和化学稳定性等优点,在催化、传感、水处理、样品前处理、生物医药以及CE分离等领域得到了广泛应用。PDA涂层的制备过程与物理吸附涂层一样简便,而表面黏附涂层的稳定性又可与共价键合涂层相媲美,因此非常适用于石英毛细管柱的修饰。更重要的是,PDA涂层较强的二次反应活性使其可作为反应平台进行灵活多样的二次表面修饰,便于构建多功能PDA涂层毛细管电色谱(CEC)固定相。基于这些突出优点,PDA涂层材料在CEC中的巨大应用价值逐渐得到了研究者们的广泛关注。该文首先对近3年有关PDA形成机理及PDA快速沉积表面化学的最新研究进展进行了总结,在此基础上综述了近10年PDA涂层材料...     

气相色谱固定相研究新进展

发展高选择性固定相是实现气相色谱(GC)高效分离样品组分及其分析测定的关键。近年,材料科学的快速发展促进了新型色谱固定相的研究和应用。该文综述了近5年有关多孔材料、石墨烯及类似物、三聚茚类材料和蝶烯类材料等作为GC固定相的研究进展,并对GC固定相研究进行了总结和展望。     

Development and application of polymeric monolithic stationary phases for capillary electrochromatography

Monolithic columns for capillary electrochromatography are receiving quite remarkable attention. This review summarizes results excerpted from numerous papers concerning this rapidly growing area with a focus on monoliths prepared from synthetic polymers. Both the simplicity of the in situ preparation and the large number of readily available chemistries make the monolithic separation media a vital alternative to capillary columns packed with particulate materials. Therefore, they are now a well-established stationary phase format in the field of capillary electrochromatography. A wide variety of synthetic approaches as well as materials used for the preparation of the monolithic stationary phases are presented in detail. The analytical potential of these columns is demonstrated with separations involving various families of compounds and different chromatographic modes.