Effect of a stirring process in an isothermal titration microcalorimeter

In this paper, it is analysed the way in which the thermodynamic results obtained in an isothermal titration microcalorimeter, with continuous injection of a liquid and a variable mass are affected. Two aspects are presented, the first one refers to a variation in the baseline that takes place when the liquid mass is increased in the laboratory cell, this variation is due to the change in the thermal coupling between the stirrer and its contact with the thermostat. The second aspect is the analysis of the effect of the stirring process and the injection velocity on the homogenization of the remaining mixture in the laboratory cell. The aim of the study of these two previous aspects is to increase the accuracy of the thermodynamic measures carried out. The variation of the baseline affects in a percentage from 1 to 2% of the total energy developed. It is also shown the necessity of a stirring process according to the injection velocity in order to obtain a homogeneous mixture at every instant. This fact allows to carry out a deconvolution of the calorimetric signal and to obtain directly the power developed in the mixture process in terms of the amount of mixed substance [Meas. Sci. Technol. 1 (1990) pp. 1285–1290; J. Thermal Analysis 41 (1994) pp. 1385–1392].