Flow-Through Microcalorimeters

Tabemer AJ, Hunter fW, Kirton RS et al. (2005) Characterization of a flow-through microcalorimeter for measuring the heat production of cardiac trabeculae. Review of Scientific Instmments 76 104902-1 7. 

Spaargaren presented a simple, low-cost, sensitive and rapidly responding flow-through microcalorimeter based on temperature difference measurements by a thermocouple [140] (see also [40,141]). The volume of the instrument could be easily adapted to the mass of the aquatic animal under investigation. Flow rate were adjusted between 1 and 10 mL per minute so that short-term changes in the environment could be realized. 

The amount adsorbed can be determined on-line by simply installing the appropriate detector at the outlet of the microcalorimeter (cf. the flow-through method for determining the adsorption isotherm). 

Groszek (1966) early developed a simple flow-through adsorption calorimeter, which is somewhat similar to a differential thermal analysis (DTA) system (because of its single-point temperature detector) and is therefore well suited for the detection of thermal effects and for screening experiments. To obtain meaningful results requires more sophisticated equipment, however. A heat flowmeter microcalorimeter is normally used for this purpose. Such a microcalorimeter, especially designed for liquid-flow adsorption and for the complementary determination of AmitH, is illustrated in Figure 5.18. 

In flow microcalorimetry the solid is placed in the microcalorimeter cell between, say two filters, and is successively brought in contact with solvent and mixtures (or solutions) of various compositions that flow through the cell or percolate over a small column of the adsorbent ). 

The flow-through mode of the microcalorimeter was used by pumping a flow of the culture-liquid from the fermenter, mixed with a flow of humidified air, through the measuring vessel of the microcalorimeter. In the flow-through mode, the measuring cell is a gold spiral with an inner volume of about 0.7 ml. The effective volume has to be determined, since it is dependent on the flow rate. 

This will be illustrated in the following example. In the study by Samuelsson and collaborators [108], the multichannel microcalorimeter (BAM) was used in the flow-through mode. The aim of the study was to compare the growth of a dentrifier (catabolic endproduct nitrogen gas). Pseudomonas fluorescens, and a dissimilatory ammonium producer (catabolic endproduct ammonium). Pseudomonas putrefaciens, during anaerobic growth in nitrate- or nitrite-... 

In flow calorimeters, samples of a culture grown in a bioreactor are continuously pumped through the measuring cell of a microcalorimeter. The sensitivity of the differential signal between the reaction vessel and the reference vessel is comparable to that obtained from microcalorimetry, e.g. [193]. From a practical point of view, they are quite flexible because they can be connected to any reactor but, due to transfer times in the minute(s) range, gas and substrate limitations must be considered. 

The reduction behaviour of the catalysts was studied in an indigenously designed TPR unit. The metal dispersion was measured by oxygen titrations using dynamic pulse flow technique (Pulse chemisorb 2700, Micromeritics, USA). Acidity and acid strength distribution were determined through heats of adsorption of ammonia by Calvet C-80 microcalorimeter (Setaram, France) and by TPD of ammonia using Catalyst Data System, Baroda (India), TPD unit. 

The details of the microcalorimeter (C-80, Setaram, France) and the procedure followed in this study are given in our earlier publications (1,2). The effluent from the sample cell was analysed with an assembly of Porapak-P and molecular sieves-5A columns, both connected in tandem and each followed by a thermal conductivity detector. Prior to calorimetric measurements, a sample was treated in situ at 475 K for 2h in H2 flow (20 ml min l), followed by evacuation (475 K, 1 h) and heating of the sanq>le for Ih under helium flow at 475 K. While maintaining a sanq)le under helium flow (20 ml min l), several successive 100 pi (4.1 pmol) pulses of CO or H2 were dosed over catalyst sanq)le through an injection port. The amount of a gas adsorbed and that of the corresponding heat evolved were recorded simultaneously. 

In flow microcalorimetry a small amount of filler is put into the cell of the calorimeter and the probe molecule passes through it in an appropriate solvent. Adsorption of the probe results in an increase of temperature and the integration of the area under the signal gives the heat of adsorption [98]. This quantity can be used for the calculation of the reversible work of adhesion according to Eq. (16). The capabilities of the technique can be further increased if a HPLC detector is attached to the microcalorimeter. The molar heat of adsorption can also be determined with this setup. 

From Eq. 1.23 it turns out that the experimental heat measured in a gas-solid open system, operating in a differential assembly of calorimetric cells, represents the enthalpy change associated to the adsorption. This result applies to adsorption processes performed in a gas-solid open system through the admission of the adsorptive on the solid material kept isothermally within a heat-flow microcalorimeter consisting of two cells in opposition. 

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