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Medium Polar Phase Chromatography
Medium Polar Phases are stationary phases whose polarity lies between unmodified and alkyl-bonded silica gels. These are usually specially modified silica gels whose selectivity can be specifically utilised. The best-known medium-polarity phases are cyano, diol, amino and nitro phases, whereby nitro phases have been almost completely eliminated from the market in recent years and are hardly available any more. A major advantage of these phases is that they can be used for both normal phase and reversed phase chromatography.
Technical Data
Cyano (nitrile) phases: Compared to unmodified silica gel, nitrile phases are less polar and have a lower retention force in normal phase mode with the same mobile phase. If these phases are used in reversed phase mode, they also show a lower retention force than C8or C18 phases. Cyano modified stationary phases have, among other things, good selectivity for substances with double bonds or aromatic compounds.
Frequently used cyano phases are, for example, the materials:
| Phase name | Modification | Particle size | Pore size | End-capping | C-content | USP | Surface area | pH range | Tmax |
| PerfectSil 120 CN | Cyano | 3, 5 µm | 120 Å | - | 7.5% | L10 | 300m2/g | 2.0-8.0 | 60 °C |
| PerfectSil Target CN-3 | Cyano | 5 µm | 100 Å | - | 7% | L10 | 450m2/g | 2.0-8.0 | 60 °C |
Diol phases: These phases have two hydroxyl groups on the surface, one primary and one secondary. This phase is therefore generally interesting for polar substances and especially for those with which hydrogen bonds can be formed.
Frequently used Diol phases are, for example, the materials:
| Phase name | Modification | Particle size | Pore size | End-capping | C-content | USP | Surface area | pH range | Tmax |
| PerfectChrom 100 Diol | Diol | 5, 10 µm | 100 Å | - | 5% | L20 | 350m2/g | 2.0-8.0 | 60 °C |
| PerfectSil 100 Diol | Diol | 5 µm | 100 Å | - | N/A | L20 | 450m2/g | 2.0-8.0 | 60 °C |
Amino phases: Amino phases have primary amino groups on the surface. As these are easily oxidised and can also undergo other chemical reactions, the following must be observed to ensure a long service life of these phases: (1.) Peroxides, which occur in diethyl ether, THF or dioxane, for example, should be avoided. (2.) Aldehydes and ketones can react with the amino groups to form imines (Schiff bases), which is why acetone, for example, should not be used as an eluent. When using aqueous mobile phases, the retention behaviour of amino phases depends on the pH value, as the NH2 group acts as a weak anion exchanger in the aqueous, acidic medium. One example of the use of amino phases is sugar analysis.
Frequently used amino phases are, for example, the materials:
| Phase name | Modification | Particle size | Pore size | End-capping | C-content | USP | Surface area | pH range | Tmax |
| PerfectSil 120 NH2 | Amino | 3, 5 µm | 120 Å | - | 4.0% | L8 | 300m2/g | 2.0-8.0 | 60 °C |
| PerfectChrom 100 NH2 | Amino | 5, 10 µm | 100 Å | - | 3.5% | L8 | 350m2/g | 2.0-8.0 | 60 °C |
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