A differential heat-conduction microcalorimeter for heat-capacity measurements of fluids

A heat-conduction calorimeter has been developed for measuring small changes in heat capacity of milligram samples of membrane lipid dispersed in water as a function of temperature. The operation of the instrument is based on the principle that the thermal response of the sample to a short (10 s), electrically generated heat burst is a function of the diffusivity of the sample. Modeling studies of the instrument's performance have revealed that the output response after the heat burst is a function of only the heat capacity, ϱC p. Calibration of the instrument experimentally confirmed this behavior. This feature obviated the need to measure the thermal conductivity in order to determine ϱC p from the diffusivity equation, η = γ/ ϱC p. The calorimeter has the following characteristics: reproducibility of loading: ± 400 μJ/C° · cm 3; baseline stability: ± 10 μJ/C° · cm 3 per 36 h; resolution (± 1 S.D.): ± 50 μJ/C° · cm 3; sample size 600 μl.