Microcalorimetry, experimental

Lantenois, S. et al.. Flow microcalorimetry Experimental development and apphcation to adsorption of heavy metal cations on silica, Appl. Surf. Sci., 253, 5807, 2007. 

E. Calvet. Microcalorimetry ofSlow Phenomena. In Experimental Thermochemistry, vol. 1 F. D. Rossini, Ed. Interscience New York, 1956 chapter 12. 

An apparatus with high sensitivity is the heat-flow microcalorimeter originally developed by Calvet and Prat [139] based on the design of Tian [140]. Several Tian-Calvet type microcalorimeters have been designed [141-144]. In the Calvet microcalorimeter, heat flow is measured between the system and the heat block itself. The principles and theory of heat-flow microcalorimetry, the analysis of calorimetric data, as well as the merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneous catalysis have been discussed in several reviews [61,118,134,135,141,145]. The Tian-Calvet type calorimeters are preferred because they have been shown to be reliable, can be used with a wide variety of solids, can follow both slow and fast processes, and can be operated over a reasonably broad temperature range [118,135]. The apparatus is composed by an experimental vessel, where the system is located, which is contained into a calorimetric block (Figure 13.3 [146]). 

Microcalorimetry studies [373] of the heat remaining in the substrate for CO(g) reaction with Pt(lll)/0 (0O = 0.25) indicate some energy release into the nascent C02. Unfortunately, these studies were done at Ts = 300 and most of the oxidation to C02 at these experimental conditions occurs at Ts = 330 K. It is likely that the authors only produced a small amount of C02 and can therefore quote only a modest lower bound to the energy release into C02. The total energy release into C02 is an important number to judge whether the experiments described below are correct. 

We have recently developed a microcalorimetric technique for quantifying the energetic changes of microorganisms colonizing a sea-water-sediment interface in experimental microcosms. The inherent low specificity of direct microcalorimetry and, moreover, the high sensitivity and reliability of modern microcalorimeters proved advantageous, since unknown and subtle events, not shown by more specific methods, may be detected. 

Experimental procedures for running excipient compatibility studies using isothermal microcalorimetry include the collection of power-time curves for each component of the mixture alone, as well as in combinations (Fig. 8). The separate drug and excipient curves can then be used to construct a theoretical non-interaction curve for the blend, which then is subtracted from the actual blend curves in order to define the interaction between the components. 

Fig. 6 Experimental observations made through microcalorimetry of autocatalysis, starting with enantiomerically pure (A), racemic (B) and 43% enantioenriched pyrimidinyl alcohol (C). Conditions as shown in the reaction scheme...

Much of the early studies of surfactant adsorption at the solid-solution interface were based on classical experimental techniques, such as solution depletion [1, 32], fluorescence spectroscopy [2], and measurements of the differential enthalpy of adsorption [2], Such methods have provided much of the basic initial understanding. However, they provide no direct structural information and are difficult to apply to mixtures [23, 34], However, when combined with other techniques, such as NMR and flow microcalorimetry, they provide some insight into the behaviour of mixtures. This was demonstrated by Thibaut et al. [33] on SDS/C10E5 mixtures adsorbed onto silica and by Colombie et al. [34] on the adsorption of SLS/Triton X-405 mixtures onto polystyrene particles. 

Experimental techniques of immersion microcalorimetry in pure liquid... 

Because of the appreciable enhancement of the adsorption potential in micropores of a few molecular diameters in width (see Section 1.7 and Figure 1.6), microcalorimetry can provide a useful means of assessing microporosity. The available experimental procedures are outlined in the following sections. 

Once the essential experimental conditions are fulfilled, it is possible to use immersion microcalorimetry for the following purposes ... 

Among them, flow adsorption microcalorimetry has been successfully used for this purpose proving to be very useful to obtain adsorption and thermodynamic data under experimental conditions close to those operating in industrial practice. 

This work compares and contrasts the experimental results using three different experimental techniques manometry, gravimetry and microcalorimetry. The system studies was the adsorption of argon, nitrogen and carhon dioxide on a NaLSX zeolite between 20 and 60°C and up to 50 bars. 

This series provides systematic and detailed reviews of topics of interest to scientists and engineers in the catalysis field. The coverage includes all major areas of heterogeneous and homogeneous catalysis, and also specific applications of catalysis such as NO control, kinetics and experimental techniques such as microcalorimetry. Each chapter is compiled by recognised experts within their specialist fields, and provides a summary of the current literature. 

Rouquerol and co-workers have recently described the experimental determination of entropies of adsorption using isothermal adsorption microcalorimetry by a slow and constant introduction of adsorbate under quasiequilibrium conditions (77) or by discontinuous introduction of the adsorbate in an open system (72). 

Rouquerol et al. (11, 12) have recently described the experimental determination of entropies of adsorption by applying thermodynamic principles to reversible gas-solid interactions. Theoretically, the entropy change associated with the adsorption process can only be measured in the case of reversible heat exchange. The authors showed how isothermal adsorption microcalorimetry can be used to obtain directly and continuously the integral entropy of adsorption by a slow and constant introduction of adsorbate under quasi-equilibrium conditions (11) or by discontinuous introduction of the adsorbate in an open system (12). 

However it is essential, in an industrial context, to have traceable and validated bases for the determination of target parameters whatever the experimental technique used. Microcalorimetry is no exception and a standard test and reference reaction has been described that fulfils this need. The imidazole-catalysed hydrolysis of triacetin has, as a result of an international multi-laboratory study, been selected as this test and... 

Recent reviews " have highlighted the capacity of microcalorimetry to provide sensitive and detailed information on the effects of processing and manipulation of dmg substances on their physicochemical properties and the extent of amorphicity present in a sample. Using lactose as an example, the amorphous content of a sample has been determined to better than 0.5% (PXRD studies can usually only determine amorphous contents at 10%). The experimentation is simple and rapid. Surface... 

R. J. Willson, Isothermal Microcalorimetry Theoretical and Experimental Developments, Ph.D. Thesis, University of Kent, 1995. 

Equations (2)-(4) show that elucidation of the rate constant requires prior knowledge of the residence time, t (the time the reacting solution spends in the calorimetric vessel) and hence the thermal volume, i.e. the operational volume of the calorimeter). Determination of reliable values for rate constants and enthalpy changes from experimental data (power, time data) for reacting systems, studied by flow microcalorimetry therefore, it requires an accurate and precise value for t at any given flow rate. This is determined from Equation (5) through knowledge of F and K. 

In spite of the evident advantages of flow microcalorimetry, this technique has been used in only a few experimental investigations of enzyme kinetics. Several references dealing with this subject are listed in Table 1. 

Fig. 6. Investigation of kinetic properties of immobilized invertase by flow microcalorimetry in the circulation mode. Initial sucrose concentration 51 mM, invertase immobilization by biospecific binding on concanavalin A-bead cellulose was prepared by binding on concana-valin A linked to chlorotriazine-activated cellulose, a Raw experimental thermometric data b data after conversion by the procedure indicated in Fig. 4. Concentrations were determined spectrophotometrically (open symbols) and by transformation of thermometric data explained in Section 5 (closed symbols) [32]...

The determination of adsorption thermodynamic quantities such as adsorption heats can now be performed through direct or indirect methods with a great degree of accuracy. The foundations of gas—solid interface calorimetry have been well established by combining adsorption microcalorimetry with adsorption in quasi-equilibrium. The experimental results reported so far, obtained from different calorimetries, concur with the values calculated from adsorption isotherms. 

Experimentally, the acid strength has been estimated by various methods such as temperature programmed desorption (TPD) of probe molecules such as microcalorimetry of adsorption of base molecules such as... 

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