Plate height observed

There have been a few reports of column efficiency and reduced plate height measurements in several unified chromatography techniques. These have been based on the apparent plate height observed at the column outlet. In the notation used by Giddings (32) the apparent plate height, H, is given by the following ... 

Because of its open, rigid structure, solvent flows through the monolithic column with relatively little resistance. The same pressure required to obtain a flow rate of 1 ml./min with 3.5-pm spherical particles provides a flow rate of 9 mL/min in the monolithic column. At 9 mL/min, the plate height in the monolithic column is only 50% greater than the minimum plate height observed at 2 mL/min. 

Fig. 5.6. Plots of plate heights against k values obtained in CEC with alkyl-benzenes (O, ) and PAHs (<>, ) as solute. Mobile phase acetonitrile-Tris.HCl (buffer 50 mM, pH 8) 90 10 (solid symbols) and 80 20 (open symbols). Column size 100 pm I.D. x 33.5 cm (effective length 25 cm). Plate heights observed at around u= 1 mm/s were plotted.

The resistance to the mass transfer term for the stationary phase will now be considered in isolation. The experimentally observed plate height (variance per unit length) resulting from a particular dispersion process [e.g., (hs), the resistance to... 

In modern TLC the distribution of sample within a spot is essentially Gaussian and the number of theoretical plates (n, ) and the plate height (H,, ) observed can be conveniently expressed ]sy equation (7.7) and (7.8)... 

CEC plate heights were smaller than observed in HPLC and essentially independent of reduced velocity. 

Perhaps more important is the observation that the kinetics of binding can contribute significantly to band spreading. If the results presented in that work are general, the kinetic plate height contribution sets a lower limit on the size of particles used in RPC at about 5 m and no practical gain in column efficiency would be made by using smaller particles. 

Direct comparison of column efficiencies of the continuous separation medium prepared in 4.5 cm long both capillary and linear channel as measured using non retained marker acetone did not reveal any difference and an identical plate height of 4-5 pm was observed for both at flow velocities of 0.5-1.5 mm/s. This indicates that there is again no substantial difference between beds formed in both formats. Obviously, the channel behaves as a capillary although it does not have the circular cross section. 

Two components, each with plate height // = 0.0025 cm, are observed to migrate to positions =10.1 cm and A = 9.9 cm, respectively, along a uniform separation column. How long must the column be to achieve unit resolution ... 

We have given a special symbol H to the observed plate height because it assumes a single measurable value in contrast to the variability of the local plate height the latter changes from point to point because of column nonuniformities. 

On HPTLC layers, the average particle size and the range of particle sizes are smaller than on TLC (e.g., 2-10 /rm and 5-17 /rm respectively for Macherey-Nagel HPTLC and TLC silica plates) and a marked fall in theoretical plate heights is observed (about one order of magnitude smaller than on standard silica layers). Consequently, smaller plate sizes (from 20 X 20 to 10 X 10 cm) and small sample volumes (from 1-3 to 0.1-0.2 juL or even less) and shorter migration distances (from 10-16 to 3-8 cm) can be employed. 

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