Structural variation of solid core and thickness of porous shell of 1.7 μm core–shell silica particles on chromatographic performance: Narrow bore columns

Chromatographic and mass transfer kinetic properties of three narrow bore columns (2.1 × 50 mm) packed with new core–shell 1.7 μm EIROSHELL™-C18 (EiS-C18) particles have been studied. The particles in each column varied in the solid-core to shell particle size ratio (ρ), of 0.59, 0.71 and 0.82, with a porous silica shell thickness of 350, 250 and 150 nm respectively. Scanning and transmission electron microscopy (SEM and TEM), Coulter counter analysis, gas pycnometry, nitrogen sorption analysis and inverse size exclusion chromatography (ISEC) elucidated the physical properties of these materials. The porosity measurement of the packed HILIC and C18 modified phases provided the means to estimate the phase ratios of the three different shell columns (EiS-150-C18, EiS-250-C18 and EiS-350-C18). The dependence of the chromatographic performance to the volume fraction of the porous shell was observed for all three columns. The naphtho[2,3-a]pyrene retention factor of k′ ∼ 10 on the three EiS-C18s employed to obtain the height equivalents to theoretical plates (HETPs) data were achieved by varying the mobile phase compositions and applying the Wilke and Chang relationship to obtain a parallel reduced linear velocity. The Knox fit model gave the coefficient of the reduce HETPs for the three EiS-C18s. The reduced plate height minimum hmin = 1.9 was achieved for the EiS-150-C18 column, and generated an efficiency of over 350,000 N/m and hmin = 2.5 equivalent to an efficiency of 200,000 N/m for the EiS-350-C18 column. The efficiency loss of the EiS-C18 column emanating from the system extra-column volume was discussed with respect to the porous shell thickness.