In this paper the temperature calibration of a Mettler Toledo DSC27HP high-pressure DSC for measurements in an ammonia atmosphere
is described. Measurements were performed on the melting process of three reference substances in golden crucibles: indium,
tin and lead. The procedure described by the German Society for Thermal Analysis and Calorimetry, GEFTA, was applied: to correct
for temperature gradients in the DSC-cel extrapolated onset temperatures of the endothermic melting peaks were measured as
a function of heating rate to find by extrapolation the extrapolated onset temperature at zero heating rate, which should
be a temperature corrected for temperature gradients. However, measurements performed at different pressures (between 1.5
and 8.4 bar) showed that the evaluated extrapolated onset temperatures at zero heating rate decreased with increasing pressure.
This observation cannot be explained by the known dependence of melting temperatures on pressure. Therefore pressure dependence
of the extrapolated onset temperatures must be caused by experimental issues. It is assumed that, although the results were
extrapolated to zero heating rate, results are still influenced by temperature gradients in the DSC-cell. As a mean value,
the extrapolated onset temperatures at zero heating rate decreased by 0.053�C when the pressure was raised by 1 bar. Since
the software package does not allow for the pressure dependence of calibration parameters, measurement results must be corrected
manually for this effect.