C18 and C18E SPE columns are the most commonly used SPE columns for various analytical tests. Not only are the names similar between the two, but also the functional groups and retention mechanisms are almost the same, which often makes people indistinguishable. So what exactly is the difference between the two?
Before that, let’s take a look at what C18 adsorbent packing materials are. C18 is a general term for a reversed-phase stationary phase linked to an octadecyl carbon chain. In addition to the common silica gel as the matrix, the reversed-phase stationary phase formed by bonding C18 chains with polymer beads, alumina, zirconia, etc. as the matrix can be called “C18”. There are many types of C18, the common silica-based C18 is usually called ODS, and the C18 that can run in pure water is called C18-AQ. The C18 packing materials are also divided into capped and uncapped.
Taking Welch Materials products as an example, Welchrom® C18 is the packing material of uncapped C18 adsorbent, and the residual silanols on the surface provide additional polar interactions, enabling the hydrophobic bonded silica to interact with the more polar adsorbents. The contact between the extracts is tighter and the retention of basic compounds and polar substances is enhanced.
Welchrom® C18E is an end-capped C18 adsorbent. It is the most hydrophobic silica-based adsorbent. It has excellent retention properties for non-polar compounds and retains most organic compounds. It is also the most widely used SPE adsorption. agent.
To sum up, in fact, the biggest difference between C18 and C18E is uncapped and capped. Compared with end-capped Welchrom® C18E, Welchrom® C18 is a general-purpose stationary phase for the extraction of polar and non-polar compounds, but C18 has the ability to retain most organic substances in water-soluble matrices, so it is less selective, It is often used to process analytes with multiple structures or very different structures. And C18E can avoid irreversible adsorption, improve recovery, and can significantly improve the chromatographic separation of basic compounds. For example, C18E small columns can usually be used instead of ion exchange columns to desalt some small molecules and some medium-sized molecules.