37
Figure A1 Description of Column Efficiency Calculations
Asymmetry is measured at 10% of the peak height and is calculated according to the
equation shown below, where a and b relate to the width of the pea section shown in Figure
1.
Two further calculations can be performed to describe column efficiency.
Reduced plate height
takes into account the particle size of the media and enables
comparison between different media types. A low value of RPH denotes good column
efficiency; a RPH of less than 6 is expected.
Where P
d
is the mean particle diameter.
Dilution factor
includes the initial sample volume in the calculation. This allows comparison
between different peak shapes. The dilution factor is given by the following equation.
Where the initial sample volume and the values of a and b are all expressed in the same
volume units.
Comparison of results should be undertaken with caution.
Different media manufacturers often express performance in terms of the definitions above.
Caution must be taken when interpreting performance results. It is advised to check not only
the media type used but also the flowrate, column diameter and bed height. Often results are
given for tests performed in laboratory scale columns.
a
b
Asymmetry
=
d
P
HETP
RPH
=
volume
sample
Initial
b
a
factor
Dilution
+
=
Summary of Contents for 100
Page 1: ...70mm 100mm and 140mm Chromatography Columns ...
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