Fullerton G D, Keener C R, Cameron I L
Department of Radiology, University of Texas HSCSA, San Antonio 78284.
J Biochem Biophys Methods. 1994 Dec;29(3-4):217-35. doi: 10.1016/0165-022x(94)90034-5.
The authors describe empirical corrections to ideally dilute expressions for freezing point depression of aqueous solutions to arrive at new expressions accurate up to three molal concentration. The method assumes non-ideality is due primarily to solute/solvent interactions such that the correct free water mass Mwc is the mass of water in solution Mw minus I.M(s) where M(s) is the mass of solute and I an empirical solute/solvent interaction coefficient. The interaction coefficient is easily derived from the constant in the linear regression fit to the experimental plot of Mw/M(s) as a function of 1/delta T (inverse freezing point depression). The I-value, when substituted into the new thermodynamic expressions derived from the assumption of equivalent activity of water in solution and ice, provides accurate predictions of freezing point depression (+/- 0.05 degrees C) up to 2.5 molal concentration for all the test molecules evaluated; glucose, sucrose, glycerol and ethylene glycol. The concentration limit is the approximate monolayer water coverage limit for the solutes which suggests that direct solute/solute interactions are negligible below this limit. This is contrary to the view of many authors due to the common practice of including hydration forces (a soft potential added to the hard core atomic potential) in the interaction potential between solute particles. When this is recognized the two viewpoints are in fundamental agreement.
作者描述了对水溶液冰点降低的理想稀释表达式的经验修正，以得出在高达3摩尔浓度时准确的新表达式。该方法假定非理想性主要是由于溶质/溶剂相互作用，因此正确的自由水质量Mwc是溶液中水的质量Mw减去I·M(s)，其中M(s)是溶质的质量，I是一个经验性的溶质/溶剂相互作用系数。该相互作用系数很容易从Mw/M(s)作为1/ΔT（冰点降低倒数）的函数的实验曲线的线性回归拟合中的常数推导出来。当将I值代入从溶液和冰中水的等效活度假设得出的新热力学表达式时，对于所有评估的测试分子（葡萄糖、蔗糖、甘油和乙二醇），在高达2.5摩尔浓度时能提供准确的冰点降低预测（±0.05℃）。浓度极限是溶质的近似单层水覆盖极限，这表明在该极限以下溶质/溶质直接相互作用可忽略不计。这与许多作者的观点相反，因为在溶质颗粒之间的相互作用势中通常包含水化力（添加到硬核原子势上的软势）。当认识到这一点时，两种观点在根本上是一致的。
