Microcalorimetric cell

III. Recording of Thermal Signals Accompanying the Fracture of a Reactionable Solid Sample in a Microcalorimetric Cell... 

THE FRACTURE OF A REACTIONABLE SOLID SAMPLE IN A MICROCALORIMETRIC CELL... 

Tight closure of this set-up, with some lubricant on O-ring (5) and with end of capillary tip of sample bulb c. 5 mm above bottom of microcalorimetric cell. 

Careful removal of sample bulb and broken tip from microcalorimetric cell... 

Two operational arrangements fulfilling the above requirements are represented in Figures 5.16b and 5.16c. For convenience, both are incorporated in a Tian-Calvet microcalorimeter with large cells (i.e. c. 100 cm3). The first device uses a disc stirrer (up and down movement) and cancels any temperature difference between the added solution and the adsorbent by placing both the adsorbent and the solution reservoir in the top part of the microcalorimetric cell (Rouquerol and Partyka, 1981). The second device uses a propeller which is given very fast half-turns (c. 10 per minute) by means of a hindered magnetic transmission which serves to damp the vibrations from the motor. 

In Figure 5.17, for a given total amount of solute n2 introduced into the microcalorimetric cell, the line I gives the dependence of the reduced surface excess amount n2w on the equilibrium molality b2. In order to plot line I we first consider the extreme case of b2 = 0, that is all the solute is considered to be adsorbed so that... 

The enthalpy of mixing, A mixH corresponds to the transient decrease in molality which takes place around the adsorbent before the molality of the added solution is eventually restored. If this change in molality is continuously recorded at the outlet of the microcalorimetric cell, then it is not difficult to carry out the integration, provided the enthalpies of mixing alone have been measured separately (Liphard eta ., 1980 Denoyel etai, 1982). 

The microcalorimetric cell, which is where the process we are studying takes place, is connected to the external enclosure through a thermoelectric cell. The cell contains platinum - rhodium-coated platinum thermocouples coimected in series and electrically isolated from the cell. There mnst be enough thermocouples to record the entire flux emitted by the internal enclosure (see Figure 6.1). 

The reactor is made up of two identical quartz tubes immersed in the two microcalorimetric cells, thus preserving the symmetry of the equipment (see Figure 6.4). 

A Tian-Calvet microcalorimeter (model BT 2.15, Setaram, France) was used to measure the enthalpies of adsorption of propane and propylene at room temperature. The samples (0.1 g) were treated under different conditions (i) vacuum at 523 K, (ii) vacuum at 773 K, (iii) He at 1073 K and (iv) H2 at 1073 K, all for 4h. Then, thqr were s ed into a Pyrex RMN tube in pure He and placed into the microcalorimetric celL A conventional manometric system coupled to the microcalorimet was used to m isare the amount adsorbed employing a (type 660) manometer witii a pr xsion of 0.001 Torr. The maximum apparent leak rate of the manometric system (including tire calorimetric cells) was 10 Torrmiri in a volume of about 60 cm. ... 

Fig. 4. Vertical cross section of a high-temperature Calvet calorimeter (16) cell guides (A) thermal insulation (B) top (C) and bottom (N) electrical heaters thermostat consisting of several metal canisters (D, G, and H) switch (E) electrical heater (F) thermometers (I, J, and K) microcalorimetric element (L) and heat sink (M).

Most calorimeters used in biochemical work and in studies of living cells and tissue pieces are usually microcalorimeters. This term is not well defined but the micro- prefix is primarily used for calorimeters with a thermal power sensitivity of 1 iW or better. The volume of a microcalorimetric (batch) vessel is usually 1-25 ml. It is common, and frequently suitable, to use typical microcalorimeters at a reduced sensitivity, for example, in work on fast growing microbial suspensions or... 

Figure 11. Electrodes in microcalorimetric vessels. A Schematic diagram of a section through a titration-perfusion microcalorimetric vessel equipped with a polarographic oxygen electrode and a pH electrode, a, sample compartment, volume 3 ml b, hollow stirrer shaft c, steel tube d, turbine stirrer e, O-rings f, combination pH electrode protected by a steel tube g, polarographic oxygen sensor (Clark electrode). B Record from a growth experiment with T-lymphoma cells. The vessel was completely filled with medium. Once the baseline had been established, the experiment was started (as indicated by the arrow) by the injection of 100 pi concentrated cell suspension.

Backman, P. WadsO, I. (1991). Cell growth experiments using a microcalorimetric vessel equipped with oxygen and pH-electrodes. J. Biochem. Biophys. Meth. 23,283-293. 

Monti, M., Hedner, P Ikomi-Kumm, J., Valdemarsson, S. (1987). Erythrocyte thermogenesis in hyperthyroid patients Microcalorimetric investigation of sodium/potassium pump and cell metabolism. Metabolism 36, 155-159. 

Perkin Elmer MPF-3 spectrofluorometer. X- and Q-band measurements of EPR spectra were carried out at liquid nitrogen and liquid helium temperatures. Microcalorimetric measurements were performed on a LKB 10700 batch microcalorimeter. Temperature-jump relaxation kinetics were measured using a double beam instrument (18) with a cell adapted for anaerobic work. The relaxation signals were fed into an H.P. 2100 computer and analyzed as described in Ref. 7. The pulse radiolysis exepriments were carried out on the 5-MeV linear accelerator at the Hebrew University. Details of the system have been published previously (19). 

In spite of usefulness of the simplification obtained by decreasing the experimental substrate concentration, many studies are aimed at the investigation of kinetic properties of immobilized biocatalysts within broader concentration ranges. In a previous paper [29], cells of Escherichia coli with penicillin acylase activity were immobilized by entrapment in calcium pectate gel and tested on the transformation of penicillin G to 6-amino penicillanic acid. Figure 9 shows experimental data from a microcalorimetric investigation of the penicillin G transformation in steady state. As appreciable particle-mass transfer was expected, the mathematical model that includes particle-mass balance was used. 

In recent years several reports have been published (24,25, 26) on microcalorimetric studies of the action of antibiotics on various microorganisms. The assay principle is that the total heat generated by the cells when fed an appropriate medium is compared with that registered when varying concentrations of the actual antibiotic are supplied. 

The apparent shape of the titration curve obtained in microcalorimetric titration experiments varies significantly, depending on the host and guest concentrations and the magnitude of the equilibrium constant. If the equilibrium constant is small and the initial reactant concentrations are low, only a small portion of the added guest can interact with the host in the cell to give a typical titration curve illustrated in Fig. 8.1. 

In the case of water pollution, the estimation of adsorption affinity of potential solid adsorbent toward the specific pollutant can be done using the so-called liquid microcalorimetry. The instruments used for this purpose are differential heat flow microcalorimeters modified to allow continuous stirring of liquid samples. The adsorbate is added to both sample and reference cells simultaneously using a programmable twin syringe pump, linked to the calorimeter. The heat evolved as a result of adsorption can be obtained by integration of the area under the calorimeter signal, for each particular injection (dose). The output of typical microcalorimetric experiment of this type is shown in Fig. 10.9. 

N. Barros, 8. Feijoo, 8. Fernandez, Microcalorimetric determination of the cell specific heat rate in soils relationship with the soil microbial population and biophysic significance. Thermochim. Acta 406,161-170 (2003). doi 10.1016/80040-6031(03)00255-7... 

G. Postole, S. Bennici, A. Auroux, Poisoning by CO of Pt/C commercial catalysts used in PEMECs. A microcalorimetric study, in Proceedings of International Symposium on Fundamentals and Developments of Fuel Cells (FDFC) 2011 Conference, ISBN 978-2-7466-2970-7... 

MICROCALORIMETRIC STUDIES OF ANIMAL TISSUES AND THEIR ISOLATED CELLS. 

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