In thermometric titrations, titrant is delivered at a constant rate, and the rate of heat evolution or absorption is substantially constant while unreacted analyte remains in the sample solution. When all analyte is consumed, the temperature rate change signals the titration endpoint. Because only the temperature rate increase or decrease is important, it is unnecessary to calibrate the sensing thermistor (although this can be done if desired). Also, it is unnecessary to use hermetically sealed calorimeter vessels; styrofoam coffee cups make ideal titration vessels in most aqueous titrations. Otherwise, polypropylene beakers or small “Thermos” flasks may be used.

The main criteria for determining the suitability of a reaction system as a candidate for thermotitrimetry are firstly that the reaction enthalpy is sufficient to obtain a meaningful temperature change over the course of the titration, and secondly that reaction kinetics are sufficiently fast to obtain accurate and reproducible endpoints. Both aqueous and non-aqueous titrations may be performed with equal facility. Potentiometric titrations (acid-base and redox), complexometric titrations, and titrations involving the formation of precipitates may be performed thermometrically. Exothermic and endothermic reactions can both be employed in thermotitrimetry.

Although thermotitrimetry can trace its origins back to the early years of the century, it is only since the advent of fast-response thermistors in the 1950’s that the technique has become of practical use to analysts. For reasons unrelated to scientific merit or practical application, thermotitrimetry has failed to have been taken up by the major manufacturers of titration equipment. The first practical exponent of the technology was the aluminium major Alcan Limited, who had developed it for the analysis of sodium aluminate solutions, used in the production of aluminium hydroxide from bauxite. The range of applications has been expanded to embrace most industrial sectors employing chemical analysis, and a niche market has been developed (principally in the USA) for “difficult to analyse” samples.

The electronic basis of the thermotitrator is a Wheatstone bridge, of which the thermistor forms one arm. A thermotitrator may consists of three modules:

•  A stepper-motor driven precision burette pump
• A control module regulating input and output signals.
• A personal computer

Antom Technologies Pty Ltd
15 Tarpon Street, The Gap, Qld 4061
AUSTRALIA

Telephone & Facsimile: +61 7 3300 2614
e-mail:   antom@globec.com.au
Internet: http://www.globec.com.au/~antom/