Itc Cell Status - MicroCal VP-ITC User Manual

Section 2: VPViewer and Origin Software
Click OK to exit and save any changes or Cancel to exit without saving any changes.
VP-ITC Numeric Display
This group of display text boxes shows the same data channels as VPViewer, as described in
section 2.3 VPViewer Main Window.

2.9 ITC Cell Status

States of Operation
The VP-ITC is a 'state driven' instrument. The current state of the ITC (cell status) is displayed
in both VPViewer and Origin. There are six unique states that comprise an ITC run,
thermostatting (idle), Seeking Temperature, PreRun Thermostat, Prestirring Equilibration, Final
Baseline Equilibration and Running. A description of each of these six states can be found
below.
Thermostatting (idle state)
When the VP-ITC is not equilibrating or performing a titration run, it sits in an idle state, the
Thermostatting State. While in the thermostatting state, the only function for the VP-ITC is to
achieve and maintain the currently defined thermostat temperature. The VP-ITC will remain in
its idle state until the operator starts a run. Access to the current thermostat temperature is
obtained through the Thermostat/Calib. Main Window tab.
Seeking Temperature (Heating/Cooling Jacket/Cells to Set Temperature)
The function of this first prerun state is to heat or cool the VP-ITC cells and adiabatic jacket to
the entered starting temperature for the experimental run. This is accomplished when the cell
temperature is within 0.1 degrees (of the entered temperature), and the DeltaT (temperature
difference between cells and adiabatic jacket) is less than 0.001 Deg. To save equilibration time
it is usually best to set the VP-ITC thermostat temperature to be the same as the starting
temperature of the ensuing run, or colder.
When filling the cells with solution prior to a run, the sample being loaded should always be
colder than the desired experimental temperature, in order to minimize the amount of time
required to equilibrate the ITC. Loading solution that is hotter than the desired run temperature
will cause for lengthy equilibrations and/or a run temperature that is slightly higher than
requested.
When the VP-ITC requires cooling to achieve the requested starting (or thermostat) temperature,
it uses a different algorithm than when it requires heating. Since there is no active cooling of the
cells or jacket, the outer shield will be used to 'pull' the jacket and cells lower in temperature
through conduction and convection inside the ITC. To increase the rate of cooling, the outer
shield will be cooled well below (10 degrees below) the requested target temperature, causing the
jacket to go well below the target temperature. Although the jacket and outer shield will be well
below the target temperature, the cells will take longer to cool and the algorithm will wait for the
cells to be below the target temperature. Once the jacket and cells are below the target
temperature they will be heated up to the requested target temperature.
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