GENERAL COMPUTER METHOD OF ANALYSIS OF CONDUCTION AND DIFFUSION IN BIOLOGICAL SYSTEMS WITH DISTRIBUTIVE SOURCES

An optimized differential heat conduction solution microcalorimeter for thermal kinetic measurements

Heat conduction calorimeters are widely used in the biological sciences, but baseline instability, low resolution, electrical noise and motion artifacts have limited their utility. Two main sources of noise, baseline fluctuation or drift and a motion artifact, were traced to amplifier drift, a small (0.015 degrees C) gradient within the constant temperature cylinder, and the method of installing the thermopiles. The addition of heaters to the top and bottom of the cylinder reduced the gradient to approximately 0.003 degrees C and greatly reduced the slow component of the motion artifact. The drift error was reduced by proper mounting of the amplifier and its external components and the enclosure of the calorimeter in a temperature-controlled box. An R-C model of the heat flow in the calorimeter was developed which was employed to discover several means of increasing sensitivity without increasing the rise-time of the calorimeter. Analysis, also based on the model, showed that variations in the air gap between the cell and cell holder can be a major source of error when the calorimeter is used to investigate the kinetics of a chemical reaction. This analysis also showed that the time for the heat to flow through the solution in the cell can be the dominant factor in determining the rise-time of the instrument. The heat conduction calorimeter described here has improved characteristics: a baseline stability of 200 nJ x s-1 (peak-to-peak) over a 48 h period; a resolution of 200 nJ x s-1; a sensitivity of 6.504 +/- 0.045 J x V-1 x s-1 referred to the sensor output; and a rise-time of 122 s for the 10-90% response.

Computer simulation for deconvolution of a heat conduction batch microcalorimeter by the D-B Finite Element Technique

The method described here is a general numerical analysis procedure which has been applied to a heat conduction Batch calorimeter for the deconvolution of its thermograms, and is based on a computer simulation of the heat conduction behavior of the instrument with time. We show by means of test signals that the method can deconvolute the signal with a resolving time that is about two orders of magnitude smaller than the time constant of the calorimeter itself. The method can be applied to time signals generally, provided that the instrument producing them can be simulated.

Fast stopped-flow microcalorimeter

A fast stopped-flow microcalorimeter using a thermistor and an a.c. bridge is described. Time resolution, limited by the response of the thermistor, is 3 ms for t 1/2 while sensitivity is 100 mu degree C in this bandpass. A reaction requires 0.3 ml of each reactant. The microcalorimeter is adiabatic to within 2% for 2 s and mixing may be repeated every 5 min. Computer finite element simulation techniques (FEST) are used to correct for the thermistor response time and heat losses. Results of tests with reactions of NaOH and HCl, NaHCO3, and HCl, and glyclyglycine and CO2 agree with published kinetic and thermodynamic values to within an experimental error of less than 2%.

Some problems concerning mixers and detectors for stopped flow kinetic studies

Images