Comparison between the efficiencies of columns packed with fully and partially porous C18-bonded silica materials

The chromatographic performance of a new brand of shell particles is compared to that of a conventional brand of totally porous silica particles having a similar size. The new material (Halo, Advanced Materials Technology, Wilmington, DE) is made of 2.7 microm particles that consist in a 1.7 microm solid core covered with a 0.5 microm thick shell of porous silica. The other material consists of the porous particles of a conventional 3 microm commercial silica-B material. These two columns have the same dimensions, 150 mm x 4.6mm. The reduced plate heights of two low molecular weight compounds, naphthalene and anthracene, two peptides (lys-bradykinin and bradykinin), and four proteins, insulin, lysozyme, beta-lactoglobulin, and bovine serum albumin were measured in a wide flow rate range and analyzed on the basis of the Van Deemter equation and of modern models for its terms. The Halo column provides a smaller axial diffusion coefficient B and a smaller eddy dispersion term A than the other column, a result consistent with its lower internal porosity (in(p)=0.19 versus 0.42) and with the narrower size distribution of its particles (sigma=5% versus 13%). The two columns have similar C terms for the two low molecular weight compounds and for the two peptides. However, the C term of the proteins that are not excluded is markedly lower on the column packed with the Halo particles than on the other column. A recent theoretical analysis of the mass transfer kinetics in shell particles predicts a C term for moderately retained proteins (3