Microcalorimetric titrations and injection enthalpimetry

Abstract

In ideal solutions, the temperature change produced by a chemical reaction in an adiabatic environment is solely a function of the relevant concentrations and independent of the volume of the sample taken for analysis This remarkable invariance is due to a compensatory effect between the integral heat evolved (or absorbed) and the heat capacity. Consequently, calorimetric methods are suited par excellence to microanalytical applications. Two alternative methodological approaches are described for the quantitative determination of inorganic materials and for organic functional group analysis, amenable to analyzing as little as 1 μmole of an unknown with a precision and accuracy of 1%, at millimolar concentration levels. Microcalorimetric titrimetry is an end-point determinative technique, utilizing breaks in automatically recorded plots of temperature versus volume of reagent added. “Injection enthalpimetry” relies on the measurement of a “heat pulse” which is proportional to the concentration of the relevant unknown. Temperature changes were determined with the aid of a semi-conductor resistance thermometer circuit, which had the sensitivity of a thousand-junction thermocouple.