User`s manual

12 Chapter 2: Installation
Calorimetry Sciences Corp.
CSC 5300 N-ITC III 13
User’s Manual
Chapter Three: Theory of Operation
Introduction to Isothermal Titration Calorimetry
There are three ways in which a calorimeter may be designed. Heat measurements may
be based on 1) a temperature rise measured in a system of known heat capacity, (ΔT);
2) the measured change in power (typically resistance heating) required to maintain a
system at a constant temperature (power compensation); and 3) a direct measure of the
heat owing between the system and large heat sink maintained at a constant temperature
(heat ow). Each method (ΔT, power compensation, and heat ow) has its advantages
and disadvantages.
The CSC Model 5300 N-ITC III uses
a differential power compensation
design for maximum sensitivity and
responsiveness. Semiconducting ther-
moelectric devices (TED) are used for
temperature control as well as to detect
temperature differences between the
sample and reference cells. A com-
puter controlled PID loop uses a heater
on the sample cell to maintain a zero
temperature difference between the
sample and reference cells (see Figure
3-1). The power required to maintain
this zero difference is used as the calo-
rimeter signal and is monitored as a
function of time. If a reaction occurs
in the sample cell that produces heat,
the heat required to maintain the zero
difference decreases by the amount of heat supplied by the reaction, resulting in a peak in
the thermogram. A typical experiment consists of several injections spaced minutes apart,
resulting in several peaks in the thermogram. The resulting incremental titration curve is
T
Sample
Cell
Reference
Cell
Thermal
Shield
TED Controlled
Block
Control
Heater
Figure 3-1: Cell Design of the CSC Model 5300 N-
ITC III.