Plate Theory and Extensions - The Maximum Sample Volume that Can Be Placed on a Chromatographic Column > Page 68

The Maximum Sample Volume that Can Be Placed on a Chromatographic Column

A sample placed on a column will initially contribute a starting variance to the peak which will continually increase during its passage through the column. The extent of the initial dispersion will depend on the sample volume and it is therefore important to know the maximum volume of charge that can be placed on the column before it significantly degenerates the column performance.

Let a volume (Vi) be injected onto a column. The volume (Vi) will be dispersed on the column in the form of a rectangular distribution. The final eluted peak will have a total variance made up of that produced by the column and other parts of the mobile phase conduit system plus that due to the finite sample volume. For convenience, the extra column dispersion (except for that from the finite sample volume), will be considered negligible.  It is now possible to apply the principle of the summation of variances to the effect of sample volume.

Thus,                               s2 = si2 + sc2       

where (s2) is the overall variance of the eluted peak,
           (si2) is the variance of the sample volume,
    and (sc2) is the variance due to column dispersion.