Baseline changes in an isothermal titration microcalorimeter

Isothermal titration microcalorimeters are submerged in an ambience at constant temperature and, this is the reason why there should not be variations in the baseline; but the experimental measures show that, in some cases, it is produced a jump in the baseline after the liquid injection. In this paper, it is studied the origin of this variation of the baseline in order to avoid it, if it is possible, or correct it and thus, to determine with the minimum error the amounts of energy or power developed in the energetic process that is being studied. The experimental results that are shown support the hypothesis that states that the cause of the baseline jump in an isothermal microcalorimeter is the variation of the thermal coupling between the content of the mixture cell and the axis of the stirrer, which is coupled, at the same time, with an area with a temperature slightly lower (in this case) than the thermostat temperature. This jump is independent from the dissipation and it always has the same sign. The magnitude of the baseline jump is variable and it mainly depends on the volume that the liquid content in a cell reaches and the placement of the stirrer within the cell, that can be changed in the handling process.