Function of separation factor:

we have noted that a fairly good separation is obtained if R = 1, but if we plot the number of plates required vs. separation factor, a curve as shown in Figure, is acquired.

Figure: Number of theoretical plates needed to achieve R = 1 plotted as a function of separation factor (α)

The curve has a very unique feature i.e., it approaches Y-axis asymptomatically, meaning thereby that if α = 1, no separation is possible however large the number of plates is. This implies that the separation will not be achieved whatever may be length of the column. If α increases above 1, the number of plates required decreases rapidly. In other words, a better separation can be achieved by bringing a small change in α by changing the liquid rather than bringing a large increase in the length of the column.