Reaction of KHP with excess NaOH or TRIS as standard reactions for calibration of titration calorimeters from 0 to 60 °C.

Calibration of titration calorimeters is an ongoing problem, particularly with calorimeters with reaction vessel volumes < 10 mL in which an electrical calibration heater is positioned outside the calorimetric vessel. Consequently, a chemical reaction with a known enthalpy change must be used to accurately calibrate these calorimeters. This work proposes the use of standard solutions of potassium acid phthalate (KHP) titrated into solutions of excess sodium hydroxide (NaOH) or excess tris(hydroxymethyl)aminomethane (TRIS) as standard reactions to determine the collective accuracy of the relevant variables in a determination of the molar enthalpy change for a reaction. KHP is readily available in high purity, weighable for easy preparation of solutions with accurately known concentrations, stable in solution, not compromised by side reactions with common contaminants such as atmospheric CO2, and non-corrosive to materials used in calorimeter construction. Molar enthalpy changes for these reactions were calculated from 0 to 60 °C from reliable literature data for the pKa of KHP, the molar enthalpy change for protonation of TRIS, and the molar enthalpy change for ionization of water. The feasibility of using these reactions as enthalpic standards was tested in several calorimeters; a 50 mL CSC 4300, a 185 µL NanoITC, a 1.4 mL VP-ITC, and a TAM III with 1 mL reaction vessels. The results from the 50 mL CSC 4300, which was accurately calibrated with an electric heater, verified the accuracy of the calculated standard values for the molar enthalpy changes of the proposed reactions.

Thermal characterization and separation of whey proteins by differential scanning calorimetry.

Most commercially available whey products contain a mixture of 6-7 whey proteins; however, there is an increased focus on using the individual whey proteins for their unique biological activities. Before extracting individual whey proteins for use, it is important to quantify how much of a particular protein is present in whey mixtures as well as if the protein is still structurally folded. We first characterized the denaturation temperature and enthalpy values for the six purified whey proteins at six pHs (3-9) and under ion chelation using a nano-differential scanning calorimeter (DSC). From the individual protein scans, we determined the optimal condition for detecting all 6 proteins on a single DSC scan was whey in an EDTA MOPs pH 6.7 buffer.