Introduction to packing particles of chromatographic column

With the continuous innovation of drugs, the structure of drugs is becoming more and more complex. It is a great challenge to develop good separation methods. As an effective detection method, HPLC has been widely used in the field of drug analysis, and the selection of chromatographic column has become the focus of attention. It is well known that the binding phase and matrix particles affect the selectivity of chromatographic column. At present, the widely used particle types are mainly divided into two types: porous silica gel particles and surface porous silica gel particles. In this paper, the packing particles of chromatographic column are briefly summarized.
Porous silica gel particles
The porous silica gel is the mainstream of the chromatographic packing matrix, and its preparation technology has been very mature. It is usually prepared by sol-gel method or stacked silica beads. Through the polymerization in the silica sol dispersion system, nano silica sol was encapsulated into organic-inorganic composite microspheres, and then sintered to remove organic matters to obtain porous silica microspheres. In order to meet the separation of complex samples and harsh experimental conditions, while maintaining the competitiveness of the company in the industry, companies continue to innovate, thus deriving a variety of types of porous silica gel particles.
1.1 organic inorganic hybrid particles
Waters company is a typical representative of organic-inorganic hybrid particle technology. It first launched Xterra series products on the market in 1999. It is based on the first generation of organic-inorganic hybrid particles liquid chromatography column. The waters global patent technology successfully solves the instability problem of silica gel matrix reverse phase packing in high pH mobile phase. Similar to the current technology for manufacturing high-purity silica gel, Xterra high-purity methylated hybrid granular materials are also obtained by chemical means of high-purity reproduction, but there is a significant difference between the two. The methylated materials are formed by condensation of two different high-purity organosiloxane monomers, which are tetraethoxysilane [TEOS] which forms SiO4 tetrahedral subunit The precursor compound] and methyltriethoxysilane [MTEOS is an organic siloxane, which is used to insert silicon carbon bonds into the entire framework of the silicon oxygen network]. It combines the advantages of silica gel and polymer packing, and has the characteristics of high separation efficiency, good peak shape, long column life and wide pH range (1 ~ 12).
Waters continued to launch the second generation hybrid granular column with Beh as its technology brand in 2005. Similar to Xterra particles, beh particles were synthesized by polycondensation between two high purity monomers. The two monomers are tetraethoxysilane [TEOS] and bis (triethoxysilyl) ethane [btee, which contains a pre-set ethylidene bridge structure]. The cross-linking degree of the second-generation hybrid particles was higher than that of the first generation Xterra hybrid particles. Therefore, the second generation hybrid particles have excellent mechanical strength.
Moreover, due to the high chemical stability and hydrophobicity of the si-ch2-ch2-si covalent unit, up to six SiO2 bonds must be broken to release one ethylidene bridge unit from the ethylidene bridge hybrid particles. Therefore, the resistance of the second generation hybrid particles to hydrolysis corrosion at high pH has been greatly improved. Beh technology was initially commercialized for acquity UPLC beh column, which resulted in exciting ultra performance liquid chromatography (UPLC) technology, and then applied to XBridge family HPLC column. Beh hybrid particle technology can provide excellent peak shape and column efficiency, especially for basic compounds. At the same time, the stability of the packing in the extreme mobile phase was improved, especially its tolerance to high pH mobile phase was greatly improved.
1.2 silica ball polymer coated particles
The polymer coated particles of silica ball are coated with a layer of polymer with uniform thickness on the surface of ultra-high-purity porous silica microspheres. The polymer film is like a layer of capsule, which reduces the influence of residual silanol group and metal impurities to the limit, thus improving the pH tolerance range and application ability of the filler. The separation efficiency of the polymer remains unchanged due to the mechanical separation of the silica gel and the silica gel particles. Xtimate reverse phase packing of Yuexu technology, Gemini NX of fillmin company and Shiseido capcell all belong to this kind of silica gel spherical polymer coated granular fillers.
1.3 surface charged hybrid particles (CSH)
Waters company innovates again on the basis of ethylidene bridge hybrid particle technology, which makes its surface carry a small amount of positive charge. In the separation system with low ionic strength, the micro positive charge on the surface repels the ionized basic compounds, which inhibits the ion exchange between the basic compounds and the residual silicon hydroxyl groups, thus obtaining excellent peak shape. This technique can also improve the loading capacity and peak capacity of samples under the condition of low ionic strength mobile phase, and retain the stable mechanical and chemical stability of ethylidene bridged particles technology. CSH technology also allows the use of formic acid instead of trifluoroacetic acid plasma pair reagent, while still maintaining the good peak shape of charged analyte, which is particularly favorable for mass spectrometry analysis.
Porous silica particles on the surface
Porous silica particles are prepared by melting the porous silica shell onto the surface of the solid silicon core. They are generally called core shell, fused core and porous shell filler. At present, the particle size of the surface porous silica gel particle chromatographic column is 2.7 μ m, which has the same separation capacity as the sub 2 μ m column used in UHPLC, and the pressure is only half of that of the sub 2 μ m column, which makes it possible to achieve the effect of ultra-high performance liquid chromatograph on conventional liquid chromatograph. The results show that the performance of the column can be improved by reducing the three parameters in Van deemer equation.
① The surface porous silica gel particles filled more evenly and reduced a value;
② Smaller particle porosity reduces axial diffusion and b value;
③ The surface porous silica gel particles can improve the heat transfer, slow down the radial temperature gradient and reduce the C value.
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