Dionex ICS-900, Руководство оператора

Страница: 128 / 142

ICS-900 Operator’s Manual
120
Doc. 065215-02 9/09
The value of k depends upon the surface area of, and distance between, the
electrode faces in the conductivity detector 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 the following:
N = 5.54(t
1
/W
1/2
)
2
Where: t
1
= the peak retention time, in seconds
W
1/2
= the peak width at 1/2 height, in seconds
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:
a = (t
2
- t
0
)/(t
1
-t
0
)
Where: t
1
and t
2
= retention time of components 1 and 2, respectively
t
0
= retention time of unretained components (void volume)
Concentrator Column
A short column used to retain and concentrate analytes from a measured volume
of relatively clean sample. This allows large volumes of sample to be injected,
lowering concentration detection limits.
Conductivity
A measure of the ease with which electrical current flows through a liquid
k l A
⁄
=