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E
Glossary
146
Dionex Aquion RFIC Operator's Manual
Cell Constant (k)
A factor determined experimentally by measuring the conductance (G) of a standard solution
of known equivalent conductivity (k).
The value of k depends upon the surface area of, and distance between, the electrode faces in
the conductivity cell.
Where: l = length
A = area of one electrode (the other electrode is equal to the first)
Channeling
The preferential flow of liquid along more open, less resistant paths through the column
packing. This causes Band Spreading.
Column Efficiency (N)
A measure of the narrowness of analyte bands as they elute from the column. High efficiency is
desirable because resolution between closely spaced bands improves with greater efficiency.
For a symmetrical (Gaussian) peak, column efficiency can be determined by:
Where: t
= the peak retention time (in seconds)
1
W
= the peak width at 1/2 height (in seconds)
1/2
Column efficiency is proportional to column length: for a given resin and column diameter,
increasing the column length increases the column efficiency. Synonymous with Theoretical
Plates.
Column Selectivity (a)
Describes the relative separation of the band maxima between two adjacent peaks. Selectivity
can be determined by the following:
Where: t
and t
= retention time of components 1 and 2, respectively
1
2
t
= retention time of unretained components (void volume)
0
κ G
⁄
k
=
l A ⁄
k
=
2
N = 5.54(t
/W
)
1
1/2
a = (t
- t
)/(t
-t
)
2
0
1
0
Thermo Scientific
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