Conical columns for liquid chromatography: A narrative review of design principles, performance benefits and renewed...

The geometry of a chromatographic column plays a central role in determining separation efficiency, speed, and practical usability. Although cylindrical columns dominate modern chromatography, alternative geometries have been proposed to address specific limitations of uniform-diameter designs. Among these, conical columns, characterised by a continuously changing internal diameter, offer a fundamentally different flow environment that directly influences solute transport and band dispersion. This article reviews the development of conical chromatographic columns and discusses the theoretical considerations required to describe separations in systems where mobile-phase velocity varies along the column axis. Experimental evidence indicates that conical columns are generally disadvantaged under simple isocratic conditions, but can provide tangible benefits in gradient elution and preparative-scale applications. Representative case examples demonstrate improved solute focusing, reduced peak tailing, higher sample loadability, and reduced consumption of stationary phase and solvents. The limited adoption of conical columns is discussed in the context of theoretical complexity and historical manufacturing constraints. Recent advances in additive manufacturing and digital design are identified as key factors that enable a revisit to non-cylindrical and hybrid column geometries, opening new possibilities for cost-efficient, high-load chromatographic separations.