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A unique C18 phase with high steric selectivity

• C18 phase with special polymeric surface modification
• particle sizes 1.8 µm, 3 µm and 5 µm
• exceptional steric selectivity
• outstanding surface deactivation
• pH stability 1 – 10
• broad range of applications: steroids, (o,p,m-) substituted aromatics, fat-soluble vitamins, positional isomers

Surface modification
By use of specific C18 silanes and appropriate polymeric bonding technologies a dense shield of alkyl chains protects the subjacent silica matrix. Elemental analysis of NUCLEODUR® C18 Isis shows a carbon load of 20%.

The target crosslinking of the C18 chains on the surface enables the separation of compounds with similar molecular structure but different stereochemical properties.

The separation of o-terphenyl and triphenylene is a concrete example to evaluate the selectivity potential of a reversed phase column in terms of the different shape of two molecules. The phenyl rings of o-terphenyl are twisted out of plane while triphenylene has a planar geometry.

Surface deactivation
The chromatography of basic analytes requires a high density of surface-bonded C18 silanes combined with a thorough endcapping procedure to keep silanol activity at a minimum. This ensures tailing-free elution of even strongly basic amino-containing compounds.

The applied special surface bonding technology also provides improved stability features for the NUCLEODUR® C18 Isis phase. The proof for this was given in a long-term test in which the decrease of plate counts for caffeine at pH 10 and 50 °C has been observed over a period of 200 hours and 2000 sample injections respectively.