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A C18 is a C18, right?

12 Jun 2014




Sorry, that actually is not true. Although many methods only list the USP code L1 for all C18 HPLC columns, there are many different varieties of C18 columns available from Restek. Here are some of the ways they may differ:


Differences in Silica

Depending on the silica particle that the C18 phase is bonded to, the column will have unique physical properties that affect its optimal range of separation and which applications work best. Pore size, carbon load and particle size are some of the most critical parameters. A different type of silica is used for each of our primary product lines for C18 columns, which are the Ultra, the Pinnacle DB, the Viva and the Raptor. Keep in mind also that the Raptor columns are based on SPP (superficially porous particle) silica, while the others are based on fully porous particles. It is also useful to note that there are different types of fully porous silica particles. We use Type A for Pinnacle DB columns and Type B for Viva and Ultra columns.


Water Tolerance

Most traditional C18 columns are subject to a phenomenon called “phase collapse” or “phase dewetting”, when exposed to a high percentage of water in the mobile phase (greater than 95%). If interested in reading more on the topic, check out John Dolan’s article, "HPLC Solutions #6: what is Phase Dewetting?"  (John Dolan's HPLC Solutions, Separation Science, 11 November 2009).  Restek sells Aqueous C18 columns that are resistant to this and can tolerate up to 100% aqueous mobile phase without adverse effects. We offer Ultra Aqueous C18 and Pinnacle DB Aqueous C18 columns that are fully water tolerant.


pH Resistance

Using a mobile phase that is too acidic or basic can cause irreversible damage to HPLC columns. A pH that is too low can cause hydrolysis and subsequent detachment of the C18 from the silica. A pH that is too high can actually begin to dissolve the silica. While the recommended pH range for most of our columns is 2.5 – 8.0, the Raptor ARC-18 can be used at a pH as low as 1.0 (full range of 1.0 -8.0). We are excited to offer this phase, which may be particularly helpful with LC-MSMS applications that require a lower pH range for mobile phase. Coupled with the quick separation of SPP, this is a great bonus.

Thank you for reading.