Abstract
Modern analytical applications of liquid chromatography require columns with higher and higher efficiencies. In this work, the general rate model (GRM) of chromatography is used for the analysis of the efficiency of core-shell phases having two porous layers with different structures and/or surface chemistries. The solution of the GRM in the Laplace domain allows for the calculation of moments of elution curves (retention time and peak width), which are used for the analysis of the efficiency of bi-layer particles with and without a non-porous core. The results demonstrate that bi-layer structures can offer higher separation power than that of the two layers alone if the inner layer has smaller surface coverage (retentivity) and the pore size and pore diffusion of the outer layer is either equal to or higher than that of the inner layer. Even in the case of core-shell phases, there is an increase in resolution by applying the bi-layer structure; however, we can always find a mono-layer core-shell particle structure with a larger core size that provides better resolution. At the optimal core size, the resolution cannot be further improved by applying a bi-layer structure. However, in case of the most widely produced general-purpose core-shell particles, where the core is ∼70% of the particle diameter, a 15–20% gain of resolution can be obtained by using well-designed and optimized bi-layer core-shell phases.
Highlights
Higher separation efficiency and faster speed have always been of great interest in high performance liquid chromatography (HPLC) [1,2,3]
Columns of superficially porous particles (SPP) [4,5] have shown even further efficiency advantages, such that some users prefer these over totally porous particles (TPP)
The aim of this paper is to investigate, by a theoretical approach, whether higher efficiency could be achieved by using multi-layer core-shell particles
Summary
Higher separation efficiency and faster speed have always been of great interest in high performance liquid chromatography (HPLC) [1,2,3]. The diameter of HPLC particles has been shrinking through the years, so that sub-2 μm totally porous particles are used widely for separating small molecules. Recent studies have reported both the advantages and disadvantages of columns packed with core-shell and totally porous sub-2 μm particles [6,7]. A critical aspect is the effect of frictional heating at ultra high pressure, causing temperature gradients within the columns [9]. The radial temperature gradient, due to the heat dissipation at the column wall, can cause significant losses in plate count [10]. Gritti et al concluded that both longitudinal and radial temperature gradients are more significant when the column length
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