Department of Food, Agricultural, and Biological Engineering, The Ohio State University, Columbus, Ohio 43210, United States.
J Phys Chem B. 2011 May 26;115(20):6564-71. doi: 10.1021/jp1110295. Epub 2011 May 4.
Direct measurements of reaction volume, so far, have been limited to atmospheric pressure. This study describes a method for in situ reaction volume measurements under pressure using a variable volume piezometer. Reaction volumes for protonic ionization of weak acid buffering agents (MES, citric acid, sulfanilic acid, and phosphoric acid) were measured in situ under pressure up to 400 MPa at 25 °C. The methodology involved initial separation of buffering agents within the piezometer using gelatin capsules. Under pressure, the volume of the reactants was measured at 25 °C, and the contents were heated to 40 °C to dissolve the gelatin and allow the reaction to occur, and cooled to 25 °C, where the volume of products was measured. Reaction volumes were used to calculate pH of the buffer solutions as a function of pressure. The results show that the measured reaction volumes as well as the calculated pH values generally quite agree with their respective theoretically predicted values up to 100 MPa. The results of this study highlight the need for a comprehensive theory to describe the pressure behavior of ionization reactions in realistic systems especially at higher pressures.
到目前为止，对反应体积的直接测量仅限于常压。本研究描述了一种在压力下使用可变体积压力计进行原位反应体积测量的方法。在 25°C 下，在高达 400 MPa 的压力下原位测量质子化弱酸性缓冲剂（MES、柠檬酸、磺胺酸和磷酸）的反应体积。该方法涉及使用明胶胶囊在压力计内初始分离缓冲剂。在压力下，在 25°C 下测量反应物的体积，并将其加热至 40°C 以溶解明胶并允许反应发生，然后冷却至 25°C，在此温度下测量产物的体积。反应体积用于计算缓冲溶液的 pH 值作为压力的函数。结果表明，测量的反应体积以及计算的 pH 值通常与各自的理论预测值非常吻合，直到 100 MPa。本研究的结果强调需要一个全面的理论来描述实际系统中电离反应的压力行为，特别是在更高的压力下。
