Let’s do a deep dive into HPLC particles. Specifically, the difference between totally porous and superficially porous materials—and why it matters for efficiency and pressure.
Quick Answer: SPS vs TPS in HPLC
Totally porous HPLC particles provide large surface area but demand high pressure at small sizes. Superficially porous (core–shell) particles shorten diffusion paths, delivering UPLC-like efficiency on standard HPLC systems.
The Original HPLC Particle: Totally Porous Silica
Since the very beginning of HPLC, we’ve used totally porous particles. Silica itself.
Think of it like a sponge. You look at the surface, and the outside is only a tiny fraction of what’s really going on inside the particle.
I like to compare LC particles to Nerf balls. Little spheres with tons of nooks and crannies. About 95% of the surface area is inside the particle.
And that’s important—because surface area is where the separation happens. That’s where we hold onto the analytes. The more surface area, the better.
What HPLC Theory Tells Us
Remember the van Deemter plot? What did van Deemter teach us?
- Smaller particles = better efficiency
- Better efficiency = better separation
- Better separation = better everything
No question. The smaller the particle, the sharper your peaks.
But here’s the problem: pressure.
- Back in the day, we used 10-micron particles.
- In the 1980s, we moved to 5 microns.
- Then came 3 microns… and eventually 1.8 microns.
Every step down gave us better efficiency—but also skyrocketing pressure requirements. Going from 3.5 µm to 1.8 µm can quadruple the pressure. If your instrument was running 2,000 PSI, suddenly you’d need 8,000 PSI.
Historically, most HPLCs couldn’t handle that. So particle size was always limited by instrument capability.
Real-World Limits
Let’s say you have a standard HPLC that maxes out around 6,000 PSI.
Meanwhile, your colleagues with UPLCs are buying 1.0-micron columns. You can’t use those—your instrument just doesn’t have the pressure capacity.
So is there another way to get UPLC-like efficiency without extreme pressure?
Yes. And that’s where superficially porous particles (SPP) come in.
What Are Superficially Porous Particles?
Superficially porous particles (sometimes called core–shell or porous shell particles) take a clever approach.
- Start with a solid, non-porous core—like a glass marble.
- Coat it with a thin porous outer layer.
For example:
- Non-porous core = 1.8 µm
- Porous shell = 0.5 µm each side
- Total particle size = 2.8 µm
From the pump’s perspective: it sees a 2.8-micron particle. Pressure stays reasonable.
From the molecule’s perspective: it only diffuses 0.5 µm deep—like working with a 1.0-micron particle.
So you get the pressure of a large particle with the efficiency of a small one. Best of both worlds.
Does It Actually Work?
Yes—pretty much exactly as advertised.
We even published a paper and presented a poster (at Pittsburgh Conference) comparing:
- 1.8 µm totally porous
- 3.5 µm totally porous
- 2.8 µm superficially porous
The SPS particles landed right in between on pressure, but gave efficiencies close to the smaller particles. Well within the range of a standard HPLC.
A Few Caveats
- Application matters. Some separations don’t work as well with superficially porous particles.
- Selectivity is the same. Manufacturers keep chemistry consistent.
- Early days had stability issues. Less of a problem now, but worth knowing.
Still—the big picture is clear: you can get UPLC-level efficiency on standard HPLC systems.
Final Thoughts: The World of Wacky Particles
So yeah—welcome to the world of HPLC details.
This is why superficially porous particles exist. They’re not hype—they’re a smart solution to a real-world pressure problem.
Sometimes theory feels abstract, but here’s proof that a little HPLC theory (thank you, van Deemter!) can explain why these new particle technologies make sense.
