Determination of the Rigorous Transfer Function of an Isothermal Titration Microcalorimeter with Peltier Compensation

An old problem in Isothermal Titration Calorimetry is the accurate characterisation of the instrument, i.e. the determination of the instrumental transfer function. Normally, this calibration is performed electrically or through well known chemical reactions, but the transfer function parameters obtained by both methods generally do not agree: the first method normally yields smaller time constants than the second one. This fact is explained by the different path the heat flux takes towards the thermal sink. However, the time constants must be independent of the experiment type (electrical or chemical). In order to attain this independency, a realistic physical model of the system is developed taking into account the different heat sources and the paths in the system and using physically attainable (experimental and theoretical) inputs for testing the model. Important results from the model study are that the instrument is represented by different transfer functions, depending on the heat source location, and that the time constants are the same, regardless of the heat source location. A very simple and fast method based on such non-phenomenological physical model for obtaining the transfer function of an Isothermal Titration Microcalorimeter is applied here.