Fused-core, sub-2 μm packings, and monolithic HPLC columns: a comparative evaluation

Three different HPLC column technologies (i.e., monolith, fused-core particles, and sub-2 mu m particles) were evaluated, comparing van Deemter plots, speed of analysis, back pressure, and mobile phase consumption. Very high linear velocities (similar to 12 mm/s) were achieved with the monolithic column using modest pressure (110 bar) at the expense of high mobile phase consumption. The minimum plate height of the monolith was similar to that of a 3 mu m-particle packed column (i.e., h = 8 mu m), operated at optimal linear velocities; the monolithic column showed substantially lower mass transfer dependence, however. The 2.7 mu m fused-core packing material yielded efficiencies closer to the sub-2 mu m material than to the 3 mu m-particle packed column and could be operated at high flow rates. The fused-core column was able to achieve linear velocities similar to those attained on the sub-2 mu m column, staying below 620 bar instead of almost near 1030 bar required by the sub-2 mu m material. The lack of pH stability of the monolithic column prevented its use to separate basic compounds (i.e., tricyclic antidepressants) at high pH. Best separation of these components at high pH was achieved using the column packed with 1.7 mu m hybrid material.