Kinetic optimisation of open-tubular liquid-chromatography capillaries coated with thick porous layers for increased loadability

The kinetic optimisation of open-tubular liquid chromatography (OTLC) columns has been revisited by taking the thick-film effects for porous coatings on retention, column resistance, band broadening and mass loadability into account. Considering the most advantageous case (i.e. where the retentive layer allows for the same high internal diffusion coefficient as conventional porous particles), calculations show the need for the development of coating procedures leading to porous films filling up approximately 50–70% of the total column diameter. Furthermore, to achieve optimum kinetic performance for separations of small molecules with total analysis times of less than 8 h (k′ = 9), total column diameters should be less than 6 μm with lengths typically greater than 0.8 m for N values of 125,000–500,000 at a pressure of 400 bar. The use of elevated temperature LC (90 °C) is also shown to increase the allowable total column diameter to up to 9 μm for a larger range of N values (100,000–880,000).