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

Abstract

The use of optical fibers in a fluorescence-detection scheme permits the accurate determination of the radial distribution of the transit time, the column eficiency, and the analyte concentration at the exit of a chromatographic axialcompression column (50 mmID). The results obtained demonstrate that the column is not homogeneous, but suggest a nearly cylindrical distribution of the packing dens@. 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 tail reminiscent of kinetic tailing.from the width of the residence time distribution is much larger (Tallarek et al., 1997), since the latter includes a contribution arising from the large-scale fluctuations of the mo-S and 0 local efficiency for column 1 along two perpendicular diameters; + and corresponding data for column 2.

Impact of retention on trans‐column velocity biases in packed columns

“…18,21,43,44 In good packed columns, the linear velocity is slightly higher in the center than at the column wall ($3-7%). In monolithic columns, the opposite is true.…”

Radial distribution of the contributions to band broadening of a silica‐based semi‐preparative monolithic column

“…It also demonstrates that the wall region of the column exhibits a greater tortuosity, as evidenced by the higher A values, and also a greater porosity, as evidenced by the smaller C values. Particle-packed columns that were previously studied [22] also exhibited a markedly heterogeneous radial distribution of the mobile phase velocity, around a fairly homogenous core. However, the mobile phase velocities in the wall region are lower than those in the core region [1,22], in contrast with what we observe for the monolithic column.…”

“…Particle-packed columns that were previously studied [22] also exhibited a markedly heterogeneous radial distribution of the mobile phase velocity, around a fairly homogenous core. However, the mobile phase velocities in the wall region are lower than those in the core region [1,22], in contrast with what we observe for the monolithic column. The effect is explained by a denser packing of the wall region due to the consequences of the heterogeneous distribution of the stress applied to the particles during the packing process and to their friction against the column wall.…”

“…A local detection method capable of mapping this distribution is therefore required. In this work, we used an electrochemical microdetector, operated in the amperometric mode [15,22,23]. This set-up is illustrated in Fig.…”

The theoretical study of the effect of packing heterogeneity on HPLC by computational fluid dynamics

“…The understanding of the effect of heterogeneous packing is a key to the improvement of large scale HPLC. Using on-column fluorescence-detection, Farkas et al found that at the exit of analytical HPLC columns, the mobile phase velocity profiles are nearly flat in the column center and falls rather rapidly towards the wall [12]; however, at the exit of an axial compression column (5 cm ID), the radial distributions of the velocity and the analyte concentration suggest a nearly parabolic distribution of the packing density [13]. The radial velocity distribution shown in Figure 4 in their work [13] is strongly curved and roughly parabolic.…”