PerkinElmer PTP-1, User Manual

Page: 38 / 54

38 . Peltier Temperature Programmer User’s Guide
Operation
WARNING
Consider the boiling points of the solvents used in the experiments.
Measurements at high temperatures can produce hazards.
When heated, tightly stoppered cells can produce an overpressure in
the cell, and an explosion may result.
CAUTION
Temperatures below room temperature can create condensation on the
cell windows and thereby affect the accuracy of the measurement. A
gentle flow of dry gas (for example, air, nitrogen) in the cell
compartment can avoid this effect.
Before explaining how the PTPs operate, the following points should be noted:
•
The PTPs can be guaranteed to reach a fixed temperature very quickly. A stable
temperature in the cell holder is obtained after 90 seconds. However, the temperature
in the cell will only be stable after a few minutes. This is due to the lower thermal
conductivity of glass (or silica) and of the sample with respect to metal. The use of
plastic cells is not recommended, particularly at high and low temperatures. Due to the
differences in thermal conductivity, a difference between the temperature of the cell
holder and that of the cell will always be present. This difference will be very low
between 20
o
C and 50
o
C, but could be relevant at the limit temperatures.
• Stirring makes it easier to reach a thermal equilibrium, and it is strongly advisable in the
case of studies of variations of spectrophotometric properties with temperature at
programmed rates. The lower the ramping rate, the less difference that will be present
between the cell holder and the cell itself.