To facilitate comparison of column performance, the concept of reduced plate height
(h) is often used. Reduced plate height is calculated as:
h = HETP/d
p
where d
p
is the mean diameter of the beads.
As a guideline, a value of h<3 is normally well acceptable at the optimal test conditions
presented above.
Asymmetry calculation
The peak should be symmetrical and the asymmetry factor as close to 1 as possible
(values between 0.8 and 1.8 are usually acceptable). A change in the shape of the peak
is usually the first indication of bed deterioration due to use.
The asymmetry factor A
s
describes the deviation from an ideal Gaussian peak shape
and is calculated from the peak width at 10% of peak height:
A
s
= b/a
The following test chromatogram shows the parameters used to calculate peak broad-
ening and peak symmetry.
0
0
0
0
-296
-
-
-
-253
0.85
-
0
20
10%
0
0
0
0
-296
-
-
-
-
0.85
-
0
0
0
0
-296
-
-
-
-
0.85
-
0
20
(measured by Absorbance or Conductivity)
50%
a b
Eluted Volume
V
R
w
h
C
on
ce
nt
ra
tio
n
AxiChrom 50, 70 and 100 columns Operating instructions 28-9331-08 AG
101
5 Operation
5.4 Performance evaluation of the column
