User`s manual

24 Chapter 4: Hardware Description
Calorimetry Sciences Corp.
CSC 5300 N-ITC III 25
User’s Manual
Figure 4-1). The power required to maintain this zero difference is used as the calorimeter
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 calibration heater located on the outside of the sample cell is used to provide precisely
controlled heat pulses for electrical calibrations and to verify instrument performance.
The entire measuring unit is encased within an insulated air-tight canister which has been
purged on a vacuum pump and lled with dry nitrogen at the factory. This is to prevent
possible condensation and evaporation of moisture around the unit which would create
excessive baseline noise.
The purge port valve on the back of the N-ITC III should remain
in the closed position at all times to maintain the integrity of the
nitrogen purge.
Reaction Vessel
The calorimeter uses two 1.0 mL reaction vessels. The reaction vessels are made of 24K
gold with platinum access tubes. The reference cell is constructed to match as closely as
possible the thermal properties of the sample cell. Accordingly, a reference needle is placed
inside the reference cell during operation to correspond to the titrant needle in the sample
cell.
Syringe/Stirrer
Two burette syringes are provided at 100 µL and 250 µL capacities, respectively. The
only difference in dimensions between the two is the inner diameter of the syringe barrel,
since the outer dimensions must be identical for proper installation in the burette.
The titrant syringe needle also functions as the stirrer and extends down into the reaction
vessel from the top when the burette is mounted. The needle is balanced for optimum stir-
ring efciency, and has two Teon bushings to help dampen stirring noise and ensure that
the needle spins true within the cell access tube (Figure 4-2).