Facts and myths about columns packed with sub-3 microm and sub-2 microm particles.

Increasing the separating efficiency enhances the separation power. The most popular solution for improving chromatographic performance is to employ columns packed with small particle diameters (i.e., sub-2 microm particles) to induce a simultaneous improvement in efficiency, optimal velocity and mass transfer, albeit the cost of pressure. In this study a systematic evaluation of the possibilities and limitations of the separations obtained with 5 cm long narrow bore columns packed with 1.5-3.0 microm particles is presented. Several commercially available different sub-3 microm and sub-2 microm packed columns were evaluated by using van Deemter, Knox and kinetic plots. Theoretical Poppe plots were constructed for each column to compare their kinetic performance. Data are presented on different polar neutral real life analytes, to show that the separation time is not obviously shorter if the particle size is reduced. Comparison of low-molecular weight compounds (one steroid and one non-steroid hormone, with molecular weights lower than 500) and a high-molecular weight one (MW approximately 1000) was conducted. Same efficiency can be achieved with columns packed with 1.9-2.1 microm particles as with smaller particles. The column packed with 3 microm particles had the lowest reduced plate height minimum (h=2.2) while the column with the smallest particles (1.5 microm) gave the highest reduced plate height minimum (h approximately 3.0). According to this study, the theoretically expected efficiency of very fine particles (diameter <2 microm) used in practice today is compromised. Investigation of this phenomenon is presented.