A brief survey is given of recent developments and current activities in isothermal microcalorimetry. The discussion focuses
on new methods in areas where the techniques have proved to be particularly useful or are promising to be so, in a near perspective.
Some problems and limitations with current methods are also discussed.
Isothermal microcalorimetry is now established as a useful technique for the characterization of the microbial activity in
soil. A brief summary of publications from this field and of instruments used in such work is presented. Several experimental
parameters that can form important sources for systematic errors are discussed and it is suggested that further method work
is made in this area. In most isothermal microcalorimetric investigations on the microbial activity in soil, the samples are
amended with glucose. It is proposed that cellulose also will be used.
Isothermal microcalorimetry has been applied as a method for predicting (in)stability of ascorbic acid and several amino acids
that undergo oxidative degradation in aqueous media. The fast and simple method involved the addition of different amounts
of hydrogen peroxide. The appearance of the heat flow curves gave a clear general indication of how stability was influenced.
The accuracy of the microcalorimetric result was investigated by comparing it with an HPLC assay and a good agreement between
the results of both methods was demonstrated. It was also established that susceptibility to oxidative degradation decreases
in the following order: cysteine, methionine, ascorbic acid, tyrosine and tryptophan.
Authors:V.-P. Lehto, M. Rahkola, E. Laine, L. Ylianttila, P. Hyssalo, and K. Jokela
The specific heat capacities (cp) for the brain and muscle equivalent liquids were determined with isothermal heat conduction microcalorimetry (IMC) and differential
scanning calorimetry (DSC). IMC was found to afford an accurate technique to measure cp for solid and liquid samples, when an appropriate reference is employed. The accuracy of obtained cp values was estimated to be better than 0.7% with the equivalent liquids. Intercomparison with a conventional isoperibolic
calorimeter showed an excellent agreement within the estimated uncertainty of the isoperibolic calorimeter (3%). Additionally,
suitability of different kinds of IMC sample vessels was tested, and the standard electrical calibration procedure of IMC
was evaluated through the determination of cp with and without a reference material.
Authors:Miha Vivoda, Robert Roškar, and Vojko Kmetec
a highly crystalline drug is of great importance, concerning drug quality and performance.
Higher sensitivity of isothermalmicrocalorimetry (IMC), compared to analytical techniques, such as X-ray powder diffraction (XRPD) and differential
Several lactose samples containing various amounts of amorphicity were studied with an isothermal microcalorimetric technique,
which allow to detect the heat and the quantity of water sorption simultaneously. As interaction with vapor is characteristic
of different surfaces, the samples were easy to be discriminated from each other by studying sorption behavior. With the crystalline
lactose samples, the amount of sorbed water was too minor to be detected reliably with the technique, but differences were
found when the energy values (J g−1) were compared. In the future work, the measurement set-up will be improved so that sorption rates less than 0.1 nmol s−1 can be measured repeatably and reliably.
The use of isothermal microcalorimetry (MC) as a sensitive monitor for slow reactions is demonstrated in a number of examples.
In Example 1 the spontaneous decomposition of a nitrate ester propellant is studied and the absolute degradation rate estimated.
Example 2 illustrates how MC can be used for comparing the rate of oxidative ageing at different O2 concentrations. Synergetic effects between oxygen and moisture in accelerated ageing of nitrile rubber are evaluated from
a so-called 4-point test in Example 3. The last example shows a simple MC technique for rapid determination of moisture permeability
through a polymeric sealant.
Authors:Y.-P. Chou, H.-Y. Hou, R.-H. Chang, M.-L. You, J.-Y. Peng, and C.-M. Shu
Cumene hydroperoxide (CHP) and its derivatives have caused many serious explosions and fires in Taiwan as a consequence of
thermal instability, chemical contamination, and even mechanical shock. It has been employed in polymerization for producing
phenol and dicumyl peroxide (DCPO). Differential scanning calorimetry (DSC) was used to analyze the thermal hazard of CHP
in the presence of sodium hydroxide (NaOH), sulfuric acid (H2SO4), and sodium bisulfite (Na2SO3). Thermokinetic parameters for decomposition, such as exothermic onset temperature (T0), maximum temperature (Tmax), and enthalpy (ΔH), were obtained from the thermal curves. Isothermal microcalorimetry (thermal activity monitor, TAM) was employed to investigate
the thermal hazards during CHP storage and CHP mixed with NaOH, H2SO4, and Na2SO3 under isothermal conditions in a reactor or container. Tests by TAM indicated that from 70 to 90 °C an autocatalytic reaction
was apparent in the thermal curves. According to the results from the TAM test, high performance liquid chromatography (HPLC)
was, in turn, adopted to analyze the result of concentration versus time. By the Arrhenius equation, the activation energy
(Ea) and rate constant (k) were calculated. Depending on the process conditions, NaOH was one of the incompatible chemicals or catalysts for CHP. When
CHP is mixed with NaOH, the T0 is induced earlier and the reactions become more complex than for pure CHP, and the Ea is lower than for pure CHP.
Calorimetry is an important thermodynamic and analytical method for investigations of living systems. The non-specific nature of calorimetry can be of advantage in such work, but will also make it difficult to interprete the results in sufficient detail. It is therefore of interest to combine calorimetry with specific analytical techniques. Work in this area is discussed with reference to the use of isothermal microcalorimetry for the characterization of living cellular systems in the pharmaceutical industry.