PDF(Pubmed)
Abstract：
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.
摘要：
滴定量热计的校准是一个持续存在的问题，特别是对于反应容器体积<10mL的量热计,其中电校准加热器位于量热容器外部。因此,必须使用具有已知焓变化的化学反应来准确地校准这些热量计。这项工作建议使用滴定到过量氢氧化钠（NaOH）或过量三（羟甲基）氨基甲烷（TRIS）溶液中的邻苯二甲酸钾（KHP）标准溶液作为标准反应，以确定相关变量的集体准确性。确定反应的摩尔焓变化。KHP易于获得高纯度，易于制备具有准确已知浓度的溶液，在溶液中稳定，不损害与常见的污染物，如大气中的二氧化碳副反应，和非腐蚀性的材料使用的热量计的建设。根据KHPpKa的可靠文献数据，从0到60°C计算这些反应的摩尔焓变化，TRIS质子化的摩尔焓变化，和水电离的摩尔焓变化。在几个热量计中测试了使用这些反应作为焓标准的可行性；50mLCSC4300，185μLNanoITC，1.4毫升VP-ITC，和具有1mL反应容器的TAMIII。50毫升CSC4300的结果是用电加热器精确校准的，验证了拟议反应的摩尔焓变化计算标准值的准确性。
