A C18 for all situations in HPLC

A C18 might be the most versatile phase and a first pick when developing analysis or purification methods for HPLC. However, when working with biomolecules and polar compounds, one may need to play with other parameters than hydrophobicity, like total charge at various pH as well as being able to run in highly aqueous conditions. In those situations, the boundaries of a traditional silica-based C18 might feel slightly too limiting. Kromasil offers therefore alternative C18 options to cover extended conditions: Kromasil EternityXT C18 and Kromasil Classic C18(w).

These two C18 alternatives are highly typical C18s when it comes to hydrophobicity, As can be seen in the Tanaka test diagram. This is also the case for IEX capacity at lower pH, while the other properties tests show differences that can give alternatives to reach separation goals.

In an example separating alkaloids, much better selectivity can be achieved at high pH when selecting Kromasil EternityXT C18, but still be confident that the stationary phase will not be impaired by running under those harsh conditions over a long time.

When separating polar compounds under reversed phase conditions, slightly different selectivity can be obtained with a wettable C18(w) compared to a classic C18. In the second example comparing the two phases, a similarly strong retention is obtained for toluene as is expected for a hydrophobic C18. On the other hand, caffeine has a notoriously weak retention on the classic C18 but is enhanced on the wettable C18(w), thanks to the polar interactions of caffeine with the polar end-capping. This can offer an advantageous edge in some situations, as well as the ability to operate in fully aqueous conditions without risk for phase dewetting.

For more condition details about the displayed examples, please visit the following pages: Separation of alkaloids and Separation of polar compounds.