Plate height elution systems

This is the basic equation for measuring plate height in elution systems. In practical use, H must be modified by a numerical constant if one chooses to use width at half-height (2t1/2, see Figure 5.6) in place of r as a measure of peak broadening. Thus... 

The width of the band eluting from the chromatographic system depends on the distance it has traveled. The proportionality factor between the two, termed height equivalent to theoretical plate (HETP), or plate height in short, is defined in the following way ... 

When the critical pair is separated, so are all other peaks in the chromatogram. If the critical pair is not the last two peaks in the chromatogram the separation time will be tR(l + nk) where n is the ratio of the retention factor of the last peak to elute in the chromatogram to the retention factor of the second peak of the critical pair. The fastest separation is obtained when tR is minimized. This will be the case if the following criteria are met. The minimum useful value for the resolution of the critical pair is accepted. The separation system is optimized to maximize the separation factor (a) for the critical pair. The retention factor for the critical pair is minimized (k 1 -5). The column is operated at the minimum value of the plate height, Hmin, corresponding to Uopt. 

Bromosulfalein (phenoltetrabromophthalein 3 ,3 -disulphonic acid disodium salt) [71-67-0] M 838.0. Purified by TLC on silica Gel G (Merck 250 i) in two solvent systems (BuOH-AcOH-H2O 30 7.5 12.5 v/v and BuOH-propionic acid- O 30 20 7.5 v/v). When the solvent reached a height of 10cm the plate was removed, dried in air and developed with NH3 vapour giving blue coloured spots. Also the dye was chromatographed on MN Silica Gel with /-BuOH- O-n-BuOH (32 10 5 v/v and visualised with a dilute KOH (or NaOH if the Na salt is required) spray. The product corresponding to bromosulfalein was scraped off and eluted with H2O, filtered and evap to dryness in a vacuum. It was dissolved in H2O and filtered through Sephadex G-25 and evaporated to dryness. and IR identification J Pharm Sci 57 819 1968 NMR Chem Pharm Bull Japan 20 581 1972 AB 83 75 1977]. 

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