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16
10. Flush the column with mobile phase before connecting it
to the detector. The length of purging will depend on
how long the column was in storage and what type of
sample and mobile phase were used. It is very important
that the column is free from silica “fines” or other
contaminants before connecting to the ELSD. The
Model 3300 ELSD will detect the contaminants with great
sensitivity.
11. After flushing the column, connect it to the LIQUID INLET
on the left side of the front panel on the detector. The
tubing between the column and the nebulizer should be a
short as possible. 0.005” i.d. inlet tubing is
recommended.
12. Turn the pump on to the desired flow rate. Do not
exceed the recommended maximum solvent rates.
13. Check connections for leaks and tighten the fittings, if
necessary.
14. Observe the signal output on the display and the
recorded baseline. After an initial large rise when the
pump is turned on, the signal level should drop close to
the “gas only” level after several minutes. If it remains
high after sufficient equilibration time, the mobile phase
may be contaminated (column fines, buffers, etc.), or the
temperature or gas flow settings may be too low for
optimal evaporation of the mobile phase. Take corrective
measures and allow the system to re-equilibrate for a few
minutes.
15. The detector is ready for sample analysis. The first time
the Model 3300 ELSD is used, you may want to
reproduce the Model 3300 ELSD QC procedure listed in
the performance documents sent with the unit.
4.5 SHUTDOWN SEQUENCE
1. Turn off the mobile phase flow.
2
. Allow gas only to flow for approximately five minutes to
clear any remaining droplets.
3. Put the detector in Standby mode
(Operation/Mode/Standby).
4. Turn off the gas supply at the source, if required.
5. Power off the ELSD using either the soft power button on
the front panel, or the main power switch on the rear
panel.
If the ELSD will not be used for several days,
disconnect the column from the nebulizer inlet and
plug the inlet. Flush the column before reconnection.
Instrument power may be left on when the instrument
is not in use. The laser may be turned by putting the
detector into Standby or Heating mode.
4.6 OPTIMIZATION PROCEDURE
1. Set the drift tube temperature, gas flow, and gain to the
initial settings recommended in Section 4.3.
2. Start mobile phase flow and allow the system to
equilibrate.
3. Increase the drift tube temperature by 1°C increments if
necessary until adequate evaporation of the mobile phase
is achieved (indicated by a stable baseline).
4. Inject the sample and obtain peak areas for each of the
components. Choose a sample concentration that shows
a peak that is on-scale with baseline noise.
5. Change the gas flow rate in 0.2L/min increments from the
recommended set point and observe the change in peak
area with each change.
6. The optimal gas flow rate will produce the largest peaks
with the lowest amount of baseline noise. Plot the signal-
to-noise ratio vs. peak area to help in identifying the
optimal gas flow rate.
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