Mass transport in sub-2-μm high-performance liquid chromatography

Ultra-high pressure liquid chromatography enables increased separation speed and efficiency. The quantitative improvement in efficiency is lower than that predicted by theory, and the reasons are not known. In this work, slow mass transport due to analyte desorption from the stationary phase is discussed as a possible contribution to the lower than expected efficiency. Data in the literature for the reversed phase elution of acetophenone, for which particle size was varied with constant particle composition and mobile phase, were used to test this possibility. The mass transport terms for the three particles sizes (1.7, 3.5 and 5.0 μm) fit well to a model that includes desorption from the stationary phase as a contribution, and this analysis yields an apparent desorption time constant of 2.0(±0.2) ms for acetophenone in a reversed-phase separation. The results indicate that it is reasonable to consider slow desorption as a possible contribution to the reduced plate height for sub-2-μm particles.