Chromatography, 2020, Vol. 38 issue (4): 372-382
DOI: 10.3724/SP.J.1123.2019.08014
Xia Hongjun, Liu Jiawei, Bai Quan*
Research progress of core-shell silica chromatographic packing
High efficiency and rapid separation and analysis is always the goal of chromatographic workers. In recent years, based on sub-2 μ m packing, monolithic column, core-shell packing and ultra-high pressure liquid chromatography technology, the rapid separation and analysis of complex samples can be realized. Although the sub-2 μ m packing has a significant advantage in the rapid separation and analysis of samples, it has great limitations to further reduce the particle size of the packing to obtain higher column efficiency. With the decrease of packing size and the increase of column pressure, it is not only difficult to fill the column, but also necessary to use the expensive ultra-high pressure liquid chromatograph. In addition, the radial temperature gradient caused by the friction heat between the mobile phase and the packing under high pressure will cause the broadening of the chromatographic peak, which limits the further improvement of the column efficiency.
Because of its special structure, silica core-shell packing can not only keep the advantages of high-efficiency and rapid separation of the existing small particle size packing, but also reduce the back pressure. It has shown excellent separation performance in the rapid analysis. In recent years, it has gradually attracted the attention of chromatographic workers. The concept of core-shell packing was put forward by Horvath at the end of 1960s. Unlike the full porous microsphere, it is a layer of porous shell wrapped outside the solid core, also known as the surface porous microsphere, as shown in Figure 1. The original intention of the design is to shorten the path of solute diffusion and maintain a low back pressure at a given velocity. The development of core-shell packing began with the preparation of a kind of thin shell microsphere with large particle size by Horvath and Lipsky and its application in ion exchange separation. Since then, the development of the microspheres has gone through several active and stagnant cycles. Kirkland has prepared the first generation of thin shell particles with controllable shell thickness and pore diameter for gas-liquid chromatography. The material has a large particle size. In 1992, with the spray drying method adopted by Agilent, the Poroshell 300 with a particle size of 5 m was successfully prepared, indicating that the core shell silica gel packing material entered the second generation. In 2006, advanced material technologies launched halo core-shell silica microspheres with a particle size of 2.7 μ m, which made the concept of core-shell microspheres formally formed. Halo core-shell silica gel chromatographic packing consists of 1.7 μ m solid silica gel core and 0.5 μ m porous shell. SiO2 Core-shell packing with a particle size of 2.7 μ M can achieve the separation efficiency of sub-2 μ m porous packing, while its back pressure is only equivalent to that of 3 μ m porous packing, and its excellent performance has attracted great attention in the whole separation field. Since the launch of halo column, Agilent, thermo and phenomenex have launched their own core-shell columns. The initial core-shell chromatographic column is mainly filled with core-shell packing with particle size of 2.6 and 2.7 μ m, and the pore diameter is about 100? (1? = 0.1nm, the same below), which is only used for the rapid separation of small molecules. Considering the influence of pore size on the separation of small molecules and biomacromolecules, most manufacturers provide two product families with different pore sizes: one with a pore size of 80-100?, which is used for the separation of small molecules. Another kind of macropore with 150-300? Is used for the rapid separation of polypeptide (150-200?) and protein (> 300?) and other biological macromolecules. In addition, the manufacturer also introduces core-shell fillers with different particle sizes, such as the smaller 2 μ m and the larger 5 μ m core-shell fillers. Higher resolution can be obtained by using sub 2 μ m core-shell packing.
Figure 1 silica core-shell microspheres with different pore structures
Fig. 1 Silica core-shell microspheres with different pore structures
Compared with sub-2 μ m porous packing, core-shell packing has the advantages of large sample loading, good column permeability and low back pressure. Compared with 5 μ m porous packing, this packing can significantly shorten the analysis time, improve the separation effect, improve the sensitivity and resolution. Therefore, the core-shell packing is considered to be a real substitute for the porous silica packing, and has become an ideal tool for the ultrafast analysis of liquid chromatography. In this paper, silica core-shell chromatographic packing was used as the core, and its separation mechanism, preparation method, application and latest development in rapid separation and analysis were reviewed, and its development was prospected.
Preparation of SiO2 @ SiO2 core-shell microspheres
The preparation of core-shell microspheres is usually realized by two or more steps. Firstly, the nonporous core was prepared, and then the porous shell was coated on the core surface. The porous shell can be formed by the aggregation of nanoparticles, nanofibers or nanorods. The pores between nanostructures are the basis of HPLC. At present, the pore structure of SiO2 core-shell microspheres can be divided into two types: one is formed by the disordered accumulation of nano-sized silica particles, the pore structure of porous shell is randomly distributed, and the pore size distribution is wide. The pore size is mainly determined by the size of nanoparticles. The random aggregation of nanoparticles forms a zigzag pore structure, as shown in Figure 1. This kind of pore structure increases the separation path of solute, and results in the broadening of peak and the increase of separation time to some extent. The other is the radioactive mesoporous channel prepared by the pseudocrystal transformation process. This kind of pore structure is formed through the pseudocrystal transformation process with the cation surfactant as the template, and has a high degree of order. The structure is shown in Figure 1. The radioactive mesoporous channel can reduce the longitudinal diffusion and improve the overall separation efficiency. The theoretical study also confirmed that this kind of radioactive mesoporous channel can effectively reduce the longitudinal diffusion of solute molecules. The following is a brief introduction of several main preparation methods.
Application of SiO2 @ SiO2 Core-shell packing
Because of its unique structure, core-shell packing has the characteristics of high column efficiency, high resolution and low back pressure in the rapid separation and analysis. It not only meets the separation requirements of high-throughput and high-resolution, but also ensures that the sample has the appropriate retention and loading. Because of its excellent chromatographic performance, it has been widely used in the rapid separation and analysis of samples in many fields such as medicine, food and environment.
expectation
As a real substitute of porous silica gel, core-shell chromatographic packing has been widely concerned for its high efficiency, high speed and low back pressure, and has been applied in the rapid separation and analysis of complex samples. The future development of core-shell packing will focus on the following aspects:
(1) Research and development of a new preparation method of silica core-shell microspheres with controllable shell thickness, adjustable pore diameter and uniform morphology. This method is easy to operate, low cost and easy to enlarge, especially for the preparation of core-shell microspheres with radioactive macropores, which are suitable for the rapid separation and analysis of biomacromolecules.
(2) Different separation modes, such as reversed phase, normal phase, hydrophilic, ion exchange chromatography, were used to further expand the new application fields of silica core-shell microspheres.
(3) The effects of shell thickness, pore size, particle size, chemical stability and surface modification of silica microspheres on the rapid separation of small molecules and biomacromolecules and their optimization.
(4) The HPLC system matched with core-shell column can ensure the best selectivity, sensitivity and column efficiency when silica core-shell column is used for rapid separation and analysis of complex samples.
China Chemical Society:
http://www.ccspublishing.org.cn/article/doi/10.3724/SP.J.1123.2019.08014
China HowNet:
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