14 Theoretical Background
Theoretical basis of 2D-LC
2D-LC User Guide 368
Peak Capacity
Peak capacity may be differently defined:
• As the maximum number of peaks that can be resolved in the available
separation space (Geometrical Definition), or
• As the ratio of the total area of the chromatogram to the area required for the
resolution of any zone (General Definition)
Geometrical
Definition
The peak capacity may be defined as the maximum number of peaks that can be
resolved in the available separation space. So peak capacity n
c
is related to the
number of theoretical plates N:
( depends on the retention time range)
In practice peaks are usually not distributed randomly over the chromatogram
and often overlap. Or in other words: In practice peaks don't fill the available
separation space evenly. This is the reason, why the number of detectable
components of a sample in 1D-LC is relatively small.
2D-LC separation offers an alternative possibility for increasing n
c
: Orthogonal
retention mechanisms generate a separation plane. Thus, the peak capacity in
2D-LC is the product of the peak capacities of the individual columns. Due to
peak broadening in 1
st
and 2
nd
dimension, components in 2D-LC are present as
two-dimensional ellipses on the retention plane.
How to calculate n
c
depends on the method:
• For comprehensive 2D-LC:
• For heart-cutting 2D-LC:
L = Separation space for dimension
ab = Area for rectangle circumscribing the ellipse on the separation plane
To Next Page
Loading...
Need help?
General
