Are sub-2 μm particles best for separating small molecules? An alternative

• 2.0 μm superficially porous particles (SPP) show advantages of sub-2 μm particles with fewer disadvantages.
• Sub-2 μm column performance reduced by instrument and column packing limitations.
• 2.0 μm SPP columns exhibit reduced plate heights equivalent to larger particles.
• 2.0 μm SPP UHPLC columns are stable to 1000 bar.
• 2.0 μm SPP have a favorable efficiency to back pressure ratio compared to sub-2 μm particles.

Superficially porous particles (SPP) in the 2.5–2.7 μm range provide almost the same efficiency and resolution of sub-2 μm totally porous particles (TPP), but at one-half to one-third of the operating pressure. The advantage of SPP has led to the introduction of sub-2 μm SPP as a natural extension of this technology. While short columns of both SPP and TPP sub-2 μm particles allow very fast separations, the efficiency advantages of these very small particles often are not realized nor sufficient to overcome some of the practical limitations and disadvantages of such small particles. Advantages and disadvantages of columns packed with sub-2 μm particles are described for comparison with the characteristics of larger particles. The authors conclude that while sub-2 μm particles have utility in research studies, columns of larger particles are often better suited for most applications. A suggested 2.0 μm superficially porous particle diameter retains many of the advantages of sub-2 μm particles, but minimizes some of the disadvantages. The characteristics of these new 2.0 μm SPP are described in studies comparing some present sub-2 μm SPP commercial columns for efficiency, column bed homogeneity and stability.