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Note the value of light intensity of measuring (
S
) channel on set wavelength and reference
(
R
) channel. Calculate the % light intensity of
S
channel to the
R
channel.
If the value
% of light intensity of
S
channel to the
R
channel is
lower than 50 %
, the cell
may be contaminated, or the mobile phase may be too absorbing. Fill cell with other mobile phase
(i.e. HPLC water). If the value of S channel is still low,
clean the cell
.
If the value
% of light intensity of
S
channel to the
R
channel is
more than 50 %
, after
elimination of the influence of absorbing the mobile phase, eventual contamination of the cell
worsens the dynamic properties of the unit (noise and drift).
Example:
At a wavelength of 254 nm with a cell AC02 filled with HPLC water, S41%, R56%
displayed on the screen. The light intensity of the S channel is 73 % from
the R channel. Purification of the cell is performed after considering the effect of
the cell contamination for LOD and LOQ.
14.3. Replacement of Cell Windows
If it is necessary to replace cracked or contaminated window, or to change the optical path of
preparative cell, unscrew the screws, remove cell covers and take out the window and the seal. To
facilitate the removal of the window, pressurize cell volume with air by help of a dry syringe.
Do not
touch the window with bare hands. Finger prints obstruct passage of UV radiation through
the cell and may damage window surface.
Insert clean windows to the cell so that required optical path is adjusted in the cell. Check for
perfect condition of gaskets and cleanness of sealing surfaces for debris of the window or any
other impurities. Damaged seals must be replaced.
After assembly,
tighten screws crosswise very carefully;
the windows may crack by excessive tightening,
therefore use solely horologic screwdriver, which does
not put on such a great momentum.
Then inspect the
optical aperture by magnifying glass for any impurities in it
(dust, hair); they might deteriorate noise of the output signal.
Prior to installation into the unit
check for cell tightness
using a syringe.
After this operation is completed flush the cell with
pure solvent. Connect the cell to the system and while a liquid flow through it observe, whether it
leaks. Check cell cleanness using the test described in above chapter.
14.4. Cleaning Cell Windows
Contamination of the cells results in lowered light transmission, which increases noise level
and makes difficulties at zeroing.
The simplest cleaning method is flushing dismantled cell with suitable solvents.
The cell
must be taken out from the instrument before washing
. Select the solvent type according to
character of contamination by a series of mutually miscible solvents. It is possible to use both
organic and inorganic solvents and diluted solutions of acids (e.g. H
2
SO
4
or HNO
3
diluted with
distilled water in ratio 1:20 to 1:10).
After this operation is completed flush the cell with pure solvent. Connect the cell to the
system and while a liquid flow through it observe, whether it leaks. Check cell cleanness using the
test described in
chapter 14.2.
If cleaning procedure by flushing did not help, address to your supplier, or replace windows
for new ones.
Содержание ECD2600
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