Radial distribution of the flow velocity, efficiency and concentration in a wide HPLC column

The use of optical fibers in a fluorescence-detection scheme permits the accurate determination of the radial distribution of the transit time, the column efficiency, and the analyte concentration at the exit of a chromatographic axial-compression column (50 mmID). The results obtained demonstrate that the column is not homogeneous, but suggest a nearly cylindrical distribution of the packing density. The average velocity close to the column wall is 7% lower than along its axis and the HETP 25% higher. The lack of homogeneity of the column packing is another source of band broadening not taken into account in chromatography so far It causes the apparent HETP derived from the conventional elution chromatogram recorded on the bulk eluent to be larger than the local HETP and the band profile to be unsymmetrical with a slight fail reminiscent of kinetic tailing.