Isocratic and gradient impedance plot analysis and comparison of some recently introduced large size core–shell and fully porous particles

• Comparison of large core–shell (≥4 μm) and fully porous (3.5 and 5 μm) particles.
• Chromatographic performance was measured using impedance and kinetic plots.
• The use of impedance plots has been extended from isocratic to gradient elution.
• A clear improvement in separation power is observed with core–shell particle columns.
• In the C-term regime the advantage of core–shell particle columns even increases.

The intrinsic kinetic performance of three recently commercialized large size (≥4 μm) core–shell particles packed in columns with different lengths has been measured and compared with that of standard fully porous particles of similar and smaller size (5 and 3.5 μm, respectively). The kinetic performance is compared in both absolute (plot of t0 versus the plate count N or the peak capacity np for isocratic and gradient elution, respectively) and dimensionless units. The latter is realized by switching to so-called impedance plots, a format which has been previously introduced (as a plot of t0/N2 or E0 versus Nopt/N) and has in the present study been extended from isocratic to gradient elution (where the impedance plot corresponds to a plot of t0/np4 versus np,opt2/np2). Both the isocratic and gradient impedance plot yielded a very similar picture: the clustered impedance plot curves divide into two distinct groups, one for the core–shell particles (lowest values, i.e. best performance) and one for the fully porous particles (highest values), confirming the clear intrinsic kinetic advantage of core–shell particles. If used around their optimal flow rate, the core–shell particles displayed a minimal separation impedance that is about 40% lower than the fully porous particles. Even larger gains in separation speed can be achieved in the C-term regime.