VP-ITC MicroCalorimeter User’s Manual
6.2 Troubleshooting
PROBLEM: Long equilibration period before an experiment starts.
There is no capability for directly cooling the cells nor the inner jacket of the VP-ITC, as was also
the case for our earlier ITC instruments. If the operator is carrying out a series of experiments in
the VP-ITC at 25.0
°
C, for example, and if the freshly loaded sample solution has a temperature
of 26.0
°
C, then there are but two choices. If the
No Check T
option in the set-up window is
checked X and the experiment started, then the system will equilibrate quickly at 26.0
°
C. If the
No Check T
option is unchecked then the software begins a process to cool the cells. This process
consists of first lowering the temperature of the outer shield (which has cooling capability) far
below 25
°
C which in time acts to lower the temperature of the inner jacket and ultimately the
cells, both of which must cool by heat transfer to the outer shield. After the cells and inner jacket
have cooled to 25
°
C, the temperature of the outer shield is cycled back up to its set position to
begin the experiment. Because heat exchange with the outer shield is slow, this process can take
a significant amount of time, even when the cell temperature only needs to be decreased by a
degree or so.
AVOIDING THE PROBLEM:
To avoid the lengthy delay in cooling the cells and still be able to operate at the desired
temperature, the operator need only control the temperature of the solution to be loaded, such that
the final temperature of the cell, after loading, is at or below the temperature where the
experiment will be carried out. When this is the case, the
No Check T
option should be left
unchecked and the cells will promptly be heated to the correct temperature (without changing the
temperature of the outer shield) so that the experiment will be ready to begin in a short time. For
experiments below room temperature, solutions should initially be cooled (after degassing)
significantly below the set temperature since they will warm up somewhat when drawn into the
loading syringe and transferred into the cell.
PROBLEM:
Baseline is stable without stirring, but becomes unstable after syringe is
inserted and stirring begins prior to injections.
SOLUTION:
Indicates a stirring problem. May be debris or bubbles in cell, bent injection syringe needle,
improper syringe height adjustment, or injection system alignment problem.
Debris or bubbles
– refill cell after rinsing or using cell cleaning apparatus and try again.
Extraordinary circumstances may require carefully inverting the entire VP-ITC unit on a suitable
stand and flushing the sample cell with the filling syringe to remove solid debris.
If your test samples are suspensions of particles try higher stirring rate to achieve uniform
suspension, although the extra noise caused by the increased stirring speed may cause
deterioration of the baseline.
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