Extra Column Dispersion - Maximum Permissible Extra Column Dispersion > Page 9

 

Thus,

 

where, dispersion due to the column alone () is

Thus, (5)

Now from (2) ,

 

Thus, substituting for () in (5),

 

(6)

 

and (7)

 

It is clear that equations (6) and (7) also gives an expression for the permissible extra column dispersion (variance and standard deviation) from all the remaining dispersion processes not associated with sample volume dispersion. The maximum sample volume and the maximum extra column variance are included in table 1 for each column. It is seen that for solutes eluted close to the dead volume, the maximum sample volume is very small, (1.57 ml for the microbore column and about 5.0 ml for the 4.6 mm I.D. and 3 mm I. D). In practice, such small sample volumes may be difficult to handle, especially if the solutes are present at trace levels. If the phase system is adjusted so that the solutes are eluted at a capacity ratio of 5, then much larger sample volumes are permissible (e.g., 9.4 ml for the microbore column and 30 ml for the large bore columns).