Kinetic performance factor - a proportional metric for comparing performance of differently structured liguid...

Particle size (d_p) of a column packing material is a subjective quantity, especially in open-tubular, monolithic, pillar-array and others non-particulate columns. It is possible to design a column internal structure so that the dimensionless plate height, h=H/d_p, could be arbitrarily small without improving the column performance. Subsequently, h is unsuitable for comparing performance of differently structured columns. The problem is avoided if previously introduced effective diameter (d_eff) of a column - a measurable (objective) parameter - is used instead of d_p. Previously introduced general definition of d_eff was suitable for LC with incompressible solvents and GC with compressible carrier gases. The latter feature complicates the concept of d_eff and its relation to other column parameters. Only LC with incompressible solvents is considered in this report. This substantially simplifies the concept of d_eff and objective performance metrics related to d_eff, including h_c=H/d_eff and kinetic performance factor (q) proportional to (1/h_c)^1/2. Moreover, the Bristow-Knox separation impedance (E) - also an objective metric - can be expressed as [Formula: see text] . Metrics q, h_c and E carry the same information, the ratio H/d_eff, only differently scaled and differently powered. However, q is the only metric proportional to external metrics like the peak capacity. Open-tubular columns (OTC) have the highest q_max among all other known structures. Having q_max close to one, OTC are convenient performance benchmark for other structures. Deficiencies of parameter h are demonstrated, properties of parameters d_eff and q_max are discussed and their numerical values found from published data for several column structures are compared.