Bio-Rad BioLogic LP System - Manual (Page 91)

• Conductivity Monitor: The Conductivity Monitor can be controlled exactly like it is in Manual mode,
except that the Flow Cell cannot be calibrated.
• Chart Recorder: The Chart Recorder can be started and stopped at any time during a run.
Note: The Chart Recorder always starts when a run begins and always stops when a run ends.
There are some operations which are not allowed during a run. Manual override operation of the Alarms
and the Valves are not allowed during a run. Changing the operation of these features can have large
effects on the run, and to use these features the run must be Paused and edited. See section 5.4.2.3 for
information on doing this.
Note: Although the Valves cannot be controlled by Manual Override, pressing the Valve instrument key dis-
plays a screen showing the state of each valve.
5.4.3 Interpreting the Chart Recorder Trace
The chart recorder trace contains the following information. Pen 1 is the UV Monitor signal and also con-
tains the event marks. Pen 2 is the Conductivity Monitor signal. When a run is started there is a special
large event mark indicating this. Each time the fraction collector is advanced there is a normal event mark.
Each time the Event Mark key is pressed there is a normal event mark.
The BioLogic LP is designed to place an extra fraction advance between collection periods when the
Diverter Valve sends the fluid to waste. The extra fraction is called the “Delay Tube”. When the Delay is set
to 0, this tube will be empty; but when the Delay is greater than 0, this tube will contain a volume equal to
the delay setting. This design is used for two reasons which are described below.
The first reason for the Delay Tube is to insure that for each gap between event marks there is a corre-
sponding fraction collected. When the fluid is diverted between two different collection periods, there is a
gap between the event mark signaling the end of the first collection period and the event mark signaling the
start of the second collection period. The Delay Tube is the tube “collected” during this time. Since this fea-
ture is present, you can count the gaps between event marks and they will correspond to the number of
fractions collected. It is important to remember that pressing the Event Mark key will cause extra event
marks to be drawn and makes counting fractions more difficult.
The second reason for the Delay Tube is only important when the Delay setting is actually used, meaning
that the delay setting is not 0. Setting the appropriate delay prevents contamination of the first fraction col-
lected after a period when fractions were not collected; i.e., there is a “gap” in collection. The potential for
this contamination occurs because the fluid which was between the Diverter Valve and the Fraction Collector
Drop Head is trapped until collection resumes, when it will be placed into the next fraction. When the appro-
priate delay is set, the Delay Tube collects this fluid instead of having it contaminate the first fraction.
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System Operation