A comparison of the performance of calorimeters

Abstract

Isothermal calorimetry is finding extensive application in a number of research areas. This popularity is reflected in the number of commercially available instruments which are capable of yielding a variety of thermodynamic and kinetic parameters. Whilst there has been much discussion of ways in which to validate any values returned from these instruments very little has been done quantitatively to compare the relative performances of different instruments. This paper highlights the use of a test and reference reaction quantitatively to compare the performance of three instruments (Thermometric TAM, THT µRC and a Setaram HSDSC III); the specifications of these instruments provide a range from high-sensitivity, long equilibration time to lower-sensitivity, short equilibration time. The comparison is made through a statistical analysis of values returned for the rate constant, enthalpy of reaction and activation energy for the base catalysed hydrolysis of methyl paraben. The statistical analysis from the data set discussed here indicates that there is no significant difference between the returned thermodynamic and kinetic parameters from the TAM and µRC. The analysis revealed however that the HSDSC returns values for the rate constant which are significantly different from both the TAM and µRC, although it is noted that this instrument was not specifically designed to operate in a step-isothermal mode and that it was possible to apply a correction to the data. In all cases the enthalpy data returned from all instruments were statistically similar although the µRC and HSDSC returned values which were, for the rate constant and activation energy, less precise than those obtained from the TAM. As well as highlighting the importance of using test and reference reactions, this study also shows that proper instrument selection is an important factor when designing a calorimetric experimental series.