The Difference Between Superficially Porous and Fully Porous Particles

Why Use a Superficially Porous Particle for HPLC Columns?

Superficially porous particles (SPPs) have a solid core surrounded by a thin, porous shell rather than porous throughout the entire particle, as is the case in traditional, fully porous particles. The solid core limits diffusion distance and improves separation speed. Superficially porous particles also have a narrow particle size distribution, improving efficiency and resolution. Another advantage of superficially porous particles is they can be used on both HPLCs and UHPLCs. Because of the variety of phases now available and the compatibility with both new and older HPLC systems, superficially porous columns are many chromatographers’ first choice when developing a new HPLC method.

Comparison of Fully and Superficially Porous Particle

Superficially porous particles offer improved efficiency and performance over similarly sized, traditional, fully porous particles. Higher efficiency of the superficially porous columns leads to improved resolution and the possibility for time savings, hence their popularity for HPLC analyses. HPLC Columns using superficially porous particles are available in a wide variety of particle sizes and stationary phase chemistries.

How Does Particle Size Affect Pressure?

Pressure increases at a rate inversely proportional to the square of the particle size. One of the primary advantages of superficially porous particles is its ability to provide increased column efficiency, often with similar or even reduced backpressure, when compared to fully porous particles. By decreasing the size of superficially porous particles, efficiency improves.

What Is Back Pressure in HPLC?

Back pressure in HPLC is typically displayed and measured in the HPLC pump. Back Pressure is the pressure created in the HPLC system from various components that cause restriction. The main source of back pressure in the HPLC system is from the HPLC Column. When using superficially porous particles, the analytes do not travel all the way through the particles in the column and, inherently, have less back pressure than a fully porous particle.

What Else Causes High Pressure in HPLC?

Other sources of system pressure in an HPLC include in-line filters, guard columns, and tubing. The amount of back pressure created by tubing is a function of the viscosity of the solvent flowing through the system, the flow rate, and the tubing’s internal diameter and length.

All tubing is made to a specific internal diameter (ID), but, of course, there are manufacturer acceptable tolerances, so a 0.005” ID tubing could actually be 0.004-.006”. In some applications, this slight difference in tubing ID can make a difference in pressure of the system.

When I first started at Chrom Tech (many years ago), a customer called and told me that the tubing they received was not the correct internal diameter. They based this on the difference in pressure when replacing the old tubing vs. the original tubing. The pieces were both to be the same internal diameter and had been cut to the exact same length, so they were surprised to see the difference in pressure with the new piece of tubing. By using the pressure drop formula with inputting the manufacturer’s minimum tubing ID tolerance and then inputting the manufacturer’s maximum ID tolerance, we were able to estimate that the tubing ID was within specifications based on the back pressure that the customer was witnessing. Please e-mail Chrom Tech if you would like us to e-mail you the Pressure Drop Formula in an excel spreadsheet to calculate your own tubing backpressure.

Which Type of HPLC Technique Is Most Widely Used?

Reversed phase chromatography is still the most popular HPLC technique, and even with the wide variety of phases now offered in Superficially Porous Columns, the Agilent Poroshell EC-C18 and SB-18 columns are Chrom Tech’s bestselling HPLC columns. The EC-C18 is an end capped C18 phase and the SB-C18 is a non-endcapped C18 phase.

Analyze Challenging Polar Compounds With Confidence

NEW Agilent InfinityLab Poroshell 120 HILIC chemistries allow you to retain and separate small, polar analytes using a standard LC system and common reversed-phase solvents. Robust Poroshell (superficially porous) particle technology offers a high-efficiency, fast analysis for increased productivity and long column lifetimes.

NEW InfinityLab Poroshell 120 HILIC-Z: A novel zwitterionic phase retains highly charged compounds, with excellent peak shape—even in high-pH or high-temperature conditions.

NEW InfinityLab Poroshell 120 HILIC-OH5: A robust poly-hydroxy fructan phase offers alternate selectivity for optimal separation of polar analytes.

For more options or information regarding Chrom Tech's liquid chromatography column portfolio and HPLC syringe filters, please contact our technical support staff today.