Agilent 1290 Infinity LC System Manual and Quick Reference
9
Introduction to Ultra-High Performance Liquid Chromatography
1
Theory of Using Smaller Particles in Liquid Chromatography
The Theory
Separation efficiency in HPLC can be described by the van Deemter equation
(
on page 9). This results from the plate-height model used to measure
the dispersion of analytes as they move down the column. H is the Height
Equivalent to a Theoretical Plate (sometimes HETP), d
p
is the particle size of
the column packing material, u
0
is the linear velocity of the mobile phase and
A, B and C are constants related to the different dispersive forces. The A term
relates to eddy diffusion or multiple flow paths through the column; B relates
to molecular diffusion along the column axis (longitudinal); C relates to mass
transfer of the analyte between the mobile and stationary phases. The
separation is at its most efficient when H is at a minimum. The effect of each
individual term and the combined equation are shown in
where the plate height is plotted against the linear flow rate through the
column. This type of plot is known as a Van Deemter Curve and is used to
determine the optimum flow rate (minimum point of the curve) for best
efficiency of separation for a column.
Figure 1
A hypothetical Van Deemter curve
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