When troubleshooting an HPLC method, one of the most common questions we hear is: “What column should I use when C18 doesn’t seem to work?”
A recent webinar, What if C18 Doesn’t work?, question from an attendee captured this perfectly:
“How does water interact with a C18 column? I want to test a water-based gel containing an aromatic compound. What’s the best column and method for this? And which solvent system works best with a Zorbax Eclipse Plus C18?”
It’s a great question, because it starts with theory but quickly becomes practical method development.
Let’s walk through the logic step by step—just as Dr. Polite explained it.
Start With the Basics: The Sample Is Not the Analyte
Chromatographers sometimes get hung up on the sample matrix—in this case a water-based gel. But from an HPLC perspective, the matrix is almost never the important part.
Once the sample is dissolved in the mobile phase and injected into the system, the analytes travel down the column independently of the matrix. Your job is simply to make sure the sample dissolves in the mobile phase you intend to use.
Water and C18 Columns: What You Actually Need to Know
Here’s the reassuring truth:
- C18 columns love water.
- Reverse-phase chromatography is literally built on using water as the weak solvent.
- Water elutes polar and semi-polar molecules beautifully.
So the idea that a water-based sample will somehow “hurt” the interaction between water and the C18 stationary phase isn’t a concern. Modern columns—especially high-quality silica-based C18 columns—are engineered to handle aqueous phases extremely well.
Why the Zorbax Eclipse Plus C18 Is a Great Choice
If you already own a Zorbax Eclipse Plus C18, congratulations—you’re working with one of Dr. Polite’s favorite columns. It’s rugged, high-efficiency, and extremely forgiving for method development.
For a water-based gel with an aromatic analyte, this column is an excellent first choice.
Recommended Method Setup
Since your sample is water-soluble, preparation is straightforward:
- Dissolve the gel directly in water or, ideally,
- Dissolve it in your mobile phase to ensure full compatibility.
Then, for your first scouting run:
Try a Gradient: 10% → 100% Organic
A typical reverse-phase gradient—such as water (A) to acetonitrile or methanol (B)—will quickly show you:
- where your peaks elute
- whether your analyte is retained
- and whether you need more or less organic strength
This simple gradient is often all you need to evaluate retention and resolution before making any refinements.
Solvent System Recommendations
The Zorbax Eclipse Plus C18 performs well with standard RP solvent systems:
- Water + Acetonitrile (most common, best peak shape)
- Water + Methanol (slightly different selectivity, sometimes better for aromatics)
If your analyte is moderately hydrophobic or aromatic, acetonitrile typically gives sharper peaks and shorter run times.
Final Takeaway
Don’t overthink the gel matrix. Focus on your analyte’s solubility and let the column do its job. With a Zorbax Eclipse Plus C18 and a simple scouting gradient, you’ll almost certainly get clean, interpretable chromatograms.
As Dr. Polite summed it up:
“Dilute your sample, make the injection—you’re going to be fine.”
