Microcalorimeters titration

Recent developments m calorimetry have focused primarily on the calorimetry of biochemical systems, with the study of complex systems such as micelles, protems and lipids using microcalorimeters. Over the last 20 years microcalorimeters of various types including flow, titration, dilution, perfiision calorimeters and calorimeters used for the study of the dissolution of gases, liquids and solids have been developed. A more recent development is pressure-controlled scamiing calorimetry [26] where the thennal effects resulting from varying the pressure on a system either step-wise or continuously is studied. 

A liquid flow microcalorimeter, the thermal activity monitor (TAM), is commercially available from ThermoMetric (formerly LKB/Bofors). This instrument consists of two glass or steel ampules with a volume of 3 to 4 cm3 (25 cm3 ampule available with a single detector), placed in a heat sink block. Recently, an injection-titration sample vessel was developed which acts as a microreactor. This vessel is provided with flow-in, flow-out, and titration lines, with a stirring device. The isothermal temperature around the heat sink is maintained by a controlled water bath. Each vessel holder, containing an ampoule, is in direct contact with a thermopile array, and the two arrays are joined in series so that their output voltages subtract. The two pairs of thermopile arrays are oppositely connected to obtain a differential output,... 

Recently there has been considerable interest on the subject of chemical test reactions for isothermal microcalorimeters. Chemical test reactions allow a user to check if an instrument is functioning correctly because they reflect more accurately the processes under study in a real experiment. Indeed, the ideal case would be to have a universally accepted chemical test reaction for each type of experiment (perfusion, titration, etc.) one may wish to investigate. Examples of systems that have been proposed as chemical test reactions include 18-crown-6/barium sulfate (2) for titration calorimetry... 

The calorimetric technique used in the titration experiment illustrated in Figure 9 allows short time intervals between the injections due to a comparatively low time constant for the instrument in combination with the electrical compensation technique. Rather, slow heat conduction microcalorimeters can be used in fast titration experiments if a dynamic correction, based on the Tian equation (equation (17)), is employed (Bastos et al., 1991 Backman et al., 1994). 

In the former case, the solid remains suspended in the liquid in the microcalorimeter cell. Then a mother solution is added, either in one step (to obtain an integral heat. A ffUnt)) or in several steps, leading to differential heats, A H(dlff)l). In the latter case one could also speak of titration calorimetry. some commercial microcalorimeters are especially constructed for such titrations. Since, with these techniques, part of the added adsorptive remains in solution, the enthalpy of dilution A yH must be subtracted it is dependent on composition and can be determined in a blank without adsorbent. The difference between A y H(int) and A y H(dlff) has been discussed before, see sec. 1.3c. 

Angberg et al. (10) studied the hydrolysis of acetyl saliclyic acid solutions, for which it was shown that elevated temperatures were needed to follow this rapid hydrolysis process. Thus, the isothermal microcalorimeter was neither more accurate, nor quicker or easier than using a conventional analytical approach, such as titration or chromatography, for this hydrolysis reaction. 

The titration cell for an isothermal microcalorimeter provides an excellent way of following complex interactions for biomaterials, polymers, and surfactants. Thus, this approach will see increasing use in the pharmaceutical sciences in the years to come. As with other calorimetric methods, there will often be parallel processes that will need to be corrected for. Furthermore, the more information that is known about a system from other methods, the easier it will be to understand the microcalorimetry data. 

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. 

TTC is performed using a MicroCal titration microcalorimeter (Northampton, MA). Solutions are degassed under vacuum prior to use. Protein at a concentration of 1 mg/mL is poured in the calorimeter cell and lipid (2.5 mg/mL) is added automatically by aliquots of 7 /integrated using the Origin software supplied by MicroCal Inc. 

A typical microcalorimeter output is shown in Figure 2 for an aqueous NaOH titration of a sulfonated silica. The molar enthalpy of neutralisation is essentially constant throughout the neutralisation and a precise value for the molar enthalpy of neutralisation can be obtained from the linear plot of cumulative enthalpy against added base. 

Despite the great diversity in the design of microcalorimeters and the experimental procedures described in the literature [1-10], only two microcalorimetric methods have found widespread application in cydodextrin (CyD) studies and drug-design research. These two methods are differential scanning calorimetry (DSC) and isothermal titration microcalorimetry (ITC). DSC and ITC can be con-... 

MicroCafs titration microcalorimeter is the most common instrument to have been used in many sdentific studies on the complexation thermodynamics of CyDs. Several important issues which should be taken into account on using a titration microcalorimeter will be discussed below for investigation of CyD complexation and supramolecular association in general. 

The greatly improved sensitivity of the modem microcalorimeters for both differential scanning miCTOcalorimetry (DSC) and isothermal titration microcalorimetry (ITC) has made their application highly useful. Titration microcalorimetry yields binding constants and, when applied as a function of temperafiire, full thermodynamic details for the binding process. DSC provides details about the distmbance of the bilayer system by the solubilized guest from which conclusions may be drawn about the preferred binding locations. 

When the time constants r and r" and T(t) are known, it is possible to determine the T (t) and T"(t) values consecutively, and thus P(t). The numerical differential correction method has also been applied to reproduce the thermokinetics in these calorimetric systems, in which time constant vary in time [258-264], such as the TAM 2977 titration microcalorimeter produced by Thermometric. These works extended the applications of the inverse filter method to linear systems with variable coefficients. In many cases [258-262], as in the multidomains method, as a basis of consideration the mathematical models used were particular forms of the general heat balance equation. 

The instrument can also be described further in terms of technical characteristics that are self-explanatory to the specialist. Examples are the titration calorimeter, bomb calorimeter, gas calorimeter, fiow calorimeter, drop calorimeter, heat flow calorimeter, and ice calorimeter. The designation microcalorimeter should be avoided because it does not show whether the term micro refers to the size of the device, the sample container, or the quantity of heat measured. 

PR Majhi, SP Moulik. Energetics of micellization Reassessment hy a high-sensitiv-ity titration microcalorimeter. Langmuir 74 3986-3990 (1998). 

Garcia-Fuentes, L. Bar6n, C. Mayorga. O.L. (2008) Influence of dynamic power compensation in an isothermal titration microcalorimeter. Anal, Chem. 70, 4615-23. 

Adsorption enthalpies were measured in a Thermal Activator Monitor (TAM), an isothermal number 2277 microcalorimeter from LKB, Sweden. It contains a 25 ml stainless steel titration cell, fitted into a single detector measuring cylinder. The cell, with a reference ampoule, was especially designed for mixing liquids and adsorption from solution. For more details, and the execution of the measurements, see [6]. Basically, the heat evolved is measured by adding the surfactant solution to the kaolinite dispersion, where the heat of dilution is subtracted as the blank. In this way a plot q isiT) of the heat evolved as a function of the amount adsorbed F is obtained. 

As it has been already mentioned, isothermal microcalorimeters are those calorimeters designed to work in the microwatt range under essentially isothermal conditions. Isothermal titration microcalorimetry (IT xC) is designed to connect extremely sensitive thermal measurement equipment (approx. 20-100 nanowatts) with an automatic syringe able to add reactants in successive injections to the solution with a precision of few nanoliters [32, 33]. Each injection produces specific heat effect, as shown in Fig. 10.5. The determination of heats evolved as a result of interaction between molecules is a main application of this variation of calorimetry. Consequently, isothermal titration calorimetry is a suitable method for studying degradations and biodegradations of versatile pollutants. 

Fig. 10.5 Typical data obtained from an isothermal titration microcalorimeter [33]...

Isothermal titration calorimetry (ITC) has long been recognized as a useful tool for the evaluation of binding constants [51]. The field of calorimetry changed markedly during the early 1990s with the introduction of commercial titration microcalorimeters [52]. These devices, available from several suppliers, operate with volumes near one to two milliliters. Virtually all the data reported to date on the thermody-... 

Figure 14. A, the specially modified sample compartment in the Thermometric TAM microcalorimeter showing the turbine with the muscle strips attached to it B, the twin heat conduction calorimeter with the insertion vessel and an identical set-up without the sample in the reference compartment. Note that the calorimeter may be used for titration (Reproduced from Reference [76] with permission).

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