# 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 (4s_{v(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.