Dispersion in Chromatography Columns - The Alternative Axes of a Chromatogram > Page 5

                                phase, the distance traveled by the solute along

                                the column and time, respectively.

and         Vr, l and tr  refer to the retention volume, column length

                                and retention time, respectively.

Now, from the Plate Theory (see Plate Theory and Extensions) it has been shown that,

Thus,                         

 

and                                   

 

Therefore,                      

 

The ratio, (), (the column length divided by the number of theoretical plates in the column) has, for obvious reasons, become termed the Height Equivalent to the Theoretical Plate (HETP) and has been given the symbol (H). However, it is seen that (H) is numerically equal to, , which is, in fact, the variance per unit length of the column. Thus, the function, , is the variance that the Rate Theory will provide an explicit equation to define and can be experimentally calculated for any column from its length and column efficiency. It follows that the equations that give a value for, (H), the variance per unit length of the column, have been termed HETP equations.