Agilent Technologies 1290 Infinity LC System System Manual And Quick Reference page 9

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Introduction to Ultra-High Performance Liquid Chromatography
Theory of Using Smaller Particles in Liquid Chromatography
The Theory
Separation efficiency in HPLC can be described by the van Deemter equation
(Figure 1 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 is the particle size of
p
the column packing material, u is the linear velocity of the mobile phase and
0
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 Figure 1 on page 9
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
Agilent 1290 Infinity LC System Manual and Quick Reference 9