Calorimetric determination of dissolution enthalpy with a novel flow-through method

Explanation and Exploration of the Isothermal Titration Curve for the NaCl + Na2SO4 + H2O System at 298.15 K and 102.2 kPa

Isothermal titration microcalorimetry (ITC) is a common and powerful tool in thermodynamics and related fields, and the connection between the solution behavior and raw titration curve is complex, important, and worth studying, so we try to discuss this problem using a complex solid-solid-liquid diagram. Although there are many experimental methods for studying ternary phase diagrams, ITC has been proven to be a simple, universal method at normal temperature and pressure. This method can be extended to investigate phase diagrams of multisalt aqueous solutions and related systems. Here, the phase equilibrium of one common ternary system (NaCl + Na₂SO₄ + H₂O) was determined using the ITC method with the aid of X-ray diffraction measurements. This isothermal and isobaric titration method can be used not only to determine the boundaries of different phase regions by analyzing changes in the slope of the observed heat vs solvent concentration plot but also to provide additional accurate data regarding the solid dissolution enthalpy and the dilution enthalpy. The dissolution enthalpy of 1 mol NaCl (Na₂SO₄) solid dissolving in water to just form a saturated solution is measured at 1.92 kJ/mol (-15.60 kJ/mol), and the dissolution enthalpy of the mixed solids can be evaluated with these data. The dilution enthalpy is strongly dependent on the solute concentration (0.08-0.23 kJ/mol at the range of concentration studied), and for the same range concentration of a solute, the dilution enthalpy of Na₂SO₄ is positive and larger than that of NaCl. Therefore, the connection between the observed heat and the microscopic behavior and the separation between the dissolution and dilution data may result in the possibility to gain a clearer understanding about the solution behaviors.

Development of a flow system for studying biofilm formation on medical devices with microcalorimetry

Isothermal microcalorimetry (IMC) is particularly suited to the study of microbiological samples in complex or heterogeneous environments because it does not require optical clarity of the sample and can detect metabolic activity from as few as 10(4) CFU/mL cells. While the use of IMC for studying planktonic cultures is well established, in the clinical environment bacteria are most likely to be present as biofilms. Biofilm prevention and eradication present a number of challenges to designers and users of medical devices and implants, since bacteria in biofilm colonies are usually more resistant to antimicrobial agents. Analytical tools that facilitate investigation of biofilm formation are therefore extremely useful. While it is possible to study pre-prepared biofilms in closed ampoules, better correlation with in vivo behaviour can be achieved using a system in which the bacterial suspension is flowing. Here, we discuss the potential of flow microcalorimetry for studying biofilms and report the development of a simple flow system that can be housed in a microcalorimeter. The use of the flow system is demonstrated with biofilms of Staphylococcus aureus.