Extra Column Dispersion - Maximum Permissible Extra Column Dispersion > Page 7

Maximum Permissible Extra Column Dispersion

The total variance of an eluted peak ()will be the sum of the variance due to column dispersion () and the variance from extra column dispersion ().

 

Thus,

 

Now, the maximum increase in peak variance from extra column dispersion that can be tolerated while not significantly effecting the resolution is 10 %. This value was suggested by Klinkenberg (3) in 1960 and has been accepted as the criteria for extra column dispersion since that time.

Thus,

or,

Substituting for () from equation (2), then for an LC column,

(3)

and, (4)

 

Values of and are included in table 1. It is seen that the permissible peak widths (taken as (4sv(k'=0))) are very smalland range from about 1.5 ml for the peak from the microbore column to about 4.8 ml for the 3 mm I.D. and 4.6 mm I.D. columns. However, it must be noted that these limits are for peaks eluted close to the dead volume (i.e.,k'=0)where the conditions are most stringent.