“…The values for the same projection in the case of a 4.6 mm × 100 mm column packed with Zorbax PRO10/150 10 μm particle size, C 18 -modified spherical silica, were about 1.7%, 1.2%, and 0.8% at flow rates of 1.0, 0.5, and 0.2 mL/min, respectively (reduced velocities, 60, 30, and 14, respectively). This contraction of the flow profile in the axial direction when the mobile phase linear velocity decreases may be a decrease of the intensity of the anastomosis or stream splitting effect, which causes a reduction of the dispersive effects induced by the radial heterogeneity of the flow. , 4 D view of the distribution of the mobile phase local linear velocity at the column outlet, at three different flow rates, overlaid. Same column as in Figure .…”
The radial distributions of the local linear velocity of
the
mobile phase, the local efficiency, and the local analyte
concentration were determined at the outlet of 0.3−0.4
in. i.d. chromatographic columns by simultaneously
recording the elution bands at different radial locations
over the column exit cross section. The flow profiles
exhibited by these columns are parabolic in shape, as was
found previously for analytical and preparative size columns. The linear velocity measured in the wall region
of
the packing is about 2−5% lower than that in the center
of the column, depending on the quality of the packed
bed. The local efficiency is highest in the core region
of
the packed bed, where local, on-column detection would
yield better separations, exhibiting a higher degree of
resolution. The radial distribution of the analyte
concentration is not uniform but shows important fluctuations
along the radius of the column. The differences in
local
linear velocity, local efficiency, and local analyte
concentration observed are the smallest for the most efficient
columns.
“…The values for the same projection in the case of a 4.6 mm × 100 mm column packed with Zorbax PRO10/150 10 μm particle size, C 18 -modified spherical silica, were about 1.7%, 1.2%, and 0.8% at flow rates of 1.0, 0.5, and 0.2 mL/min, respectively (reduced velocities, 60, 30, and 14, respectively). This contraction of the flow profile in the axial direction when the mobile phase linear velocity decreases may be a decrease of the intensity of the anastomosis or stream splitting effect, which causes a reduction of the dispersive effects induced by the radial heterogeneity of the flow. , 4 D view of the distribution of the mobile phase local linear velocity at the column outlet, at three different flow rates, overlaid. Same column as in Figure .…”
The radial distributions of the local linear velocity of
the
mobile phase, the local efficiency, and the local analyte
concentration were determined at the outlet of 0.3−0.4
in. i.d. chromatographic columns by simultaneously
recording the elution bands at different radial locations
over the column exit cross section. The flow profiles
exhibited by these columns are parabolic in shape, as was
found previously for analytical and preparative size columns. The linear velocity measured in the wall region
of
the packing is about 2−5% lower than that in the center
of the column, depending on the quality of the packed
bed. The local efficiency is highest in the core region
of
the packed bed, where local, on-column detection would
yield better separations, exhibiting a higher degree of
resolution. The radial distribution of the analyte
concentration is not uniform but shows important fluctuations
along the radius of the column. The differences in
local
linear velocity, local efficiency, and local analyte
concentration observed are the smallest for the most efficient
columns.
“…According to the random walk theory (8), which is admittedly based upon a highly simplified model, the transcolumn parameters may be expressed as WaV (12) where is the fractional velocity bias, µ/µ, between the fluid in the wall region and that in the central core of the column. Equation 12illustrates the idea, which may or may not be generally correct, that the trans-column parameters contain a common factorizable dependence upon p. Generalizing, we may be able to write = "0 ( ); = ".0 ( ) (13) Thus the trans-column contributions to h could be expressed as…”
“…In the same paper he also provided conclusive evidence against the classical theory by using chromatographic data obtained with liquid carriers. Also studying liquid column chromatography, Gordon et al (15) found evidence consistent with the coupled eddy diffusion theory, but they felt that with gas carriers this effect would be noticed only at velocities much higher than those found in gas chromatography columns.…”
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