药物溶液渗透压的理论及测定方法研究

Osmotic pressure of drug solutions is now usually measured by the freezing point osmometry and the dew point osmometry, which are based on colligative properties measurements. .The freezing point osmometry is limited by the solubility of solutes at freezing point temperature. Thus, this method is only appropriate for dilute solutions. The commercial available dew point osmometer is also only appropriate for dilute solutions. This is ascribed to that a concentrated solution has a low relative humidity, and insufficient water condenses onto the thermocouple during the cooling period and the temperature change will be lower than the minimum detection value. Additionally, both the freezing point osmometer and the dew point osmometer are very complicated and expensive..In the present project, another method named air humidity in equilibrium method is proposed to determine the osmotic pressure of drug solutions. In this method, the osmotic pressure is determined by the measurement of the relative air humidity in equilibrium with the solution. .Compared with freezing point osmometry, the newly proposed method eliminates the solubility problem because of no temperature change in the method. Compared with the commercial available dew point osmometer, the humidity meter we used overcomes the minimum detection value difficulty in concentrated range. Actually, the humidity meter we used has a better performance in high concentration range. .The pocket humidity meter complements commercial available osmometers especially in the high-osmotic-pressure region, and most importantly, it is significantly simpler and cheaper..Because osmotic pressure is one of the colligative properties, it is possibly calculated from the concentration in diluted solutions, or from the activity in concentrated solutions theoretically. In the present project, we will try to calculate the activity from the concentration of solutions according to physicochemical models and then calculate the osmotic pressure. From this study we not only understand deeply the physicochemical theory, but also get a control for our osmotic pressure measurement. We find no control measurement in concentrated range other than theoretic calculation, because no other method can determine osmotic pressure in that range.

目前国内外通常是测定溶液的冰点或蒸气的露点来间接测定药物溶液的渗透压，仪器十分复杂昂贵，而且都只能适用于稀溶液。我们在上一国家自然科学基金项目的研究中因遇到困难而意外地发现，用湿度计直接测定与药物溶液呈平衡的空气的相对湿度，就可测得溶液的渗透压。渗透压是稀溶液的依数性质，在很稀的溶液中，渗透压与药物浓度成正比。在较浓的溶液中，若能从药物浓度计算出水的活度，就可以从理论上计算出药物溶液的渗透压。在本项目中，我们将1)建立一种测定药物溶液渗透压的新方法。此法简便快速且价廉，其测定原理比现有方法更为科学合理。由于避免了冰点法和露点法的方法限制、测定困难和近似计算，新方法可适用于较高浓度的药物溶液。2)用物理化学模型从理论上计算药物溶液的渗透压，这即能丰富人们对基础物理化学现象的认识，又能用理论计算值与新方法的测定值互相对照，以解决现有方法不能测定较高浓度下的渗透压，不能用来与新方法对照的困难。

目前国内外通常是测定溶液的冰点或蒸气的露点来间接测定药物溶液的渗透压，仪器十分复杂昂贵，而且都只能适用于稀溶液。我们在上一国家自然科学基金项目的研究中因遇到困难而意外地发现，用湿度计直接测定与药物溶液呈平衡的空气的相对湿度，就可测得溶液的渗透压。渗透压是稀溶液的依数性质，在很稀的溶液中，渗透压与药物浓度成正比。在较浓的溶液中，若能从药物浓度计算出水的活度，就可以从理论上计算出药物溶液的渗透压。.按照本项目的研究计划，我们1)建立了一种测定药物溶液渗透压的新方法。此法简便快速且价廉，其测定原理比原有方法更为科学合理。由于避免了冰点法和露点法的方法限制、测定困难和近似计算，新方法可适用于较高浓度的药物溶液；2)用物理化学模型从理论上计算药物溶液的渗透压，这即能丰富人们对基础物理化学现象的认识，又能用理论计算值与新方法的测定值互相对照，以解决原有方法不能测定较高浓度下的渗透压，不能用来与新方法对照的困难。