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What’s in a name? A C18 by any other name would not be the ARC-18

23 Sep 2018

You have probably read or been told numerous times and in numerous ways that not all C18 columns are the same. And that is very true. Particle morphology, bonding chemistry, and add-ons like end capping all influence the retention and selectivity of this workhorse LC phase. At Restek we have an interesting C18 phase that we call the ARC-18 that I would like extol upon if I may.

The name ARC-18 is descriptive of one of its most useful characteristics. I actually had the pleasure of coming up with this name (a love/hate task for any product manager). The “AR” in ARC-18 stands for “Acid Resistant” which is very descriptive of this C18 phase. Through steric hindrance or the add on of bulky side groups near the ligand connection to the silica the bond is protected from the attack of acidic mobile phases that can cleave off the C18 and cause your columns to lose retention.


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The acid resistance of a sterically protected C18 is well documented. We often describe this in comparison to non-protected C18s. And its advantages are highly sought after. Especially when you want a long lasting and stable column for LC-MS/MS where the mobile phases are typically acidic. An area where that is particularly important is in the analysis of peptides. My colleagues here at Restek did some fantastic research to demonstrate how the acid resistance of the ARC-18 allows for the flexibility of acidic adjustments to optimize peptide analysis. 

While there are other sterically protected C18s on the market you may find that these phases are also end capped. Encapping is typically done to prevent analyte interaction with the silica surface which can cause secondary retention exhibited as peak tailing. We found that C18s that were both sterically hindered and end capped (e.g. TMS) could take longer to equilibrate and therefore increase your run time. The endcapping can also cause the peak shape of some basic compounds to suffer. We wanted a C18 with a well-balanced retention profile for many different types of compounds like pesticide panels.

Another area where this phase shines is in cannabis potency analysis. We have demonstrated excellent LC-UV separation for 16 Cannabinoids on both our Raptor 2.7 (shown below) and 1.8µm columns utilizing the unique selectivity of the ARC-18 phase.

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16 Cannabinoids on Raptor 2.7µm ARC-18

So if you need a robust C18 column for LC-MS/MS, a selective column for cannabis potency, a well-balanced C18 for a wide array of pesticides, or a versatile column for peptides, have a look at the ARC-18. It is truly ahead of the curve.