Plate Theory and Extensions - The Position of the Points of Inflection > Page 56

The Position of the Points of Inflection

In order to measure the column efficiency, the position of the points of inflection, where the peak width is to be measured, must be identified. The inflection points are not easily located on a peak, so it is necessary to know the fraction of the peak height at which they occur. The peak represents the concentration profile of the eluting solute, so the fraction of the peak height at which the points of inflexion are located will be the ratio of the solute concentration after () plate volumes of mobile phase has passed through the column to the solute concentration after (n) plate volumes of mobile phase have passed through the column.

Therefore, if (f) is the fraction of the height (h) at which the points of inflection occur, then

                                       

Replacing and with elution function that describes them,

                                                      

                                             

                                              

                                                  

           Thus,                             (50)

    Now, if x<<1,            

Consequently, since (n) will always be greater than 100,