Analysis on the types and selection principles of chromatogr

In the analysis of modern high performance liquid chromatography, the separation effect largely depends on the selection of chromatographic packing. However, the selection range of chromatographic packing is very wide. To make a suitable choice, we must have a certain understanding of this. The packing of liquid chromatography can be inorganic matrix with ceramic property or organic polymer matrix. The inorganic matrix is rigid and not easy to expand in solvent. The organic matrix is mainly silica gel and alumina. The organic polymer matrix in the packing of liquid chromatography mainly includes crosslinked styrene divinylbenzene and polymethacrylate. The organic polymer matrix is small in rigidity and easy to compress, and the solvent or solute is easy to penetrate into the organic matrix, which leads to the expansion of packing particles, thus reducing the mass transfer and finally reducing the column efficiency.

The following is a brief introduction to the properties of three kinds of matrix which are widely used in liquid chromatography

1) Silica gel matrix
Silica gel matrix is a common matrix in HPLC packing. In addition to its high strength, it also provides a surface that can be bonded to various ligands by mature silylation technology to form packing materials for reversed-phase, ion-exchange, hydrophobic, hydrophilic or molecular exclusion chromatography. Silica based fillers are suitable for a wide range of polar and nonpolar solvents. The disadvantage is that it is unstable in alkaline water-soluble mobile phase. In general, the recommended pH range for conventional analysis of silica based fillers is 2-8.

2) Alumina matrix
Alumina matrix has the same good physical properties as silica gel and can withstand a wide range of pH. It is also rigid and does not shrink or expand in solvents. However, unlike silica gel, alumina bonded phase is unstable in aqueous mobile phase. However, alumina bonded phase which is stable in aqueous phase has been found and shows pH stability.

3) Polymer matrix
Polymer matrix fillers based on styrene divinylbenzene or polymethacrylate with high crosslinking degree are used for HPLC under ordinary pressure, and their pressure limits are lower than those of inorganic fillers. Styrene divinylbenzene matrix has strong hydrophobicity. Any mobile phase, stable over the entire pH range, can be cleaned with NaOH or strong alkali. Methacrylate matrix is essentially more hydrophobic than styrene divinylbenzene, but it can be modified to hydrophilic by appropriate functional groups. The matrix is not as acid and alkali resistant as styrene divinylbenzene, but it can also withstand repeated washing at ph13.

All polymer matrices expand or contract when the mobile phase changes. The expansion and contraction of polymer fillers with high cross-linking degree used in HPLC should be limited. Solvents or small molecules are easy to penetrate into polymer matrix, because the mass transfer of small molecules in polymer matrix is slower than that in ceramic matrix, so the column efficiency of small molecules in this matrix is low. For macromolecules such as proteins or synthetic polymers, polymer matrix is more effective than ceramic matrix. Therefore, polymer matrix is widely used to separate macromolecular substances.

The selection of matrix for liquid chromatography generally follows the following rules: silica gel matrix packing is used for most HPLC analysis, especially for small molecular weight analytes; polymer packing is used for high molecular weight analytes, mainly used to make molecular exclusion and ion exchange columns.Analysis on the types and selection principles of chromatographic column packing in liquid chromatography

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