Enthalpimetric analysis

Figure 5. Temperature measuring circuit (thermistor bridge) and adiabatic cell for enthalpimetric analysis...

The analysis of the sorption isotherms is the most common way to study the interactions of water with polymers. Mathematical models can be fitted to the experimental results and give information about these water-polymer interactions which can be directly obtained from enthalpimetric analysis. It is possible to get the heat of sorption of the water molecules during different sorption isotherms corresponding to different humidity levels. It is also possible to check the phase transformations of the absorbed water by differential scanning calorimetry. 

After the intensive development of air-segmented flow analysis, some successful analytical procedures without stream segmentation were proposed, mainly in connection with enthalpimetric [29,30], chem-iluminometric [31] or spectrophotometric [32,33] detection. In these systems the time domain involved was generally short, thus air addition and removal was not performed. Either the sample or the wash solution was continuously aspirated towards the main channel and measurements were made under an almost steady state situation. Without air-segmentation, however, sample throughput was impaired and sample changing was cumbersome. 

C. Pasquini and W. A. de Oliveira, Comparison of Merging Zones, Injection of Reagent and Single-Line Manifolds for Enthalpimetric Flow Injection Analysis. Anal. Chim. Acta, 156 (1984) 307. 

In enthalpimetric flow injection analysis, the sample pulses employed are too small to give a thermal steady state, but result in a temperature peak proportional to the enthalpy change and thereby to the substrate concentration. The peak height, the area under the peak, and the ascending slope of the peak are all linearly related to the substrate concentration. Sample introduction of a sufficient duration (several minutes) leads to a thermal steady state resulting in a constant temperature deviation, which is also proportional to the substrate concentration. 

A large number of enthalpimetric assays based on immobilized enzyme reactors have been proposed with potential interest to biotechnology, clinical chemistry, and food analysis. Several of these have been applied in bioprocess monitoring and recently bedside monitoring of glucose and urea have been... 

See also Flow Injection Analysis Principles. Sensors Overview Amperometric Oxygen Sensors Calorimetric/ Enthalpimetric Chemically Modified Electrodes Microorganism-Based Photometric. 

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