Salameh Adnan K, Taylor Lynne S
Industrial and Physical Pharmacy, School of Pharmacy, Purdue University, West Lafayette, Indiana 47907, USA.
J Phys Chem B. 2006 May 25;110(20):10190-6. doi: 10.1021/jp0612376.
Mixtures of deliquescent solids are susceptible to deliquescence lowering, where water vapor condensation occurs in mixtures at a lower critical relative humidity (RH(0mix)) than individual component critical relative humidities (RH(0)s). The purpose of this study was to evaluate the effect of deliquescence lowering on chemical reactivity. Sucrose, citric acid and their physical mixtures were characterized using vapor sorption analysis to determine RH(0) and RH(0mix). Acid-catalyzed sucrose hydrolysis kinetics was determined using polarimetric analysis. Physical mixtures of sucrose and citric acid crystals were prepared and stored at various relative humidities at 22 degrees C. For these physical mixtures, sucrose hydrolysis was found to occur only when the environmental RH exceeded RH(0mix). Degradation kinetics correlated with the storage RH, being fastest at higher RH. In addition, a lag period was initially observed, which was most prominent for samples stored close to RH(0mix). With exposure to RHs below RH(0mix), no sucrose degradation was detected over the experimental time period. In conclusion, mixtures of deliquescent solids showed increased water sorption at lower RHs, which caused solid dissolution and subsequently led to an increase in the chemical reactivity.
潮解性固体混合物易发生潮解降低现象，即混合物中水蒸气的凝结发生时的临界相对湿度（RH(0mix)）低于各组分的临界相对湿度（RH(0)s）。本研究的目的是评估潮解降低对化学反应性的影响。使用蒸汽吸附分析法对蔗糖、柠檬酸及其物理混合物进行表征，以确定RH(0)和RH(0mix)。采用旋光分析测定酸催化蔗糖水解动力学。制备了蔗糖和柠檬酸晶体的物理混合物，并在22℃下于不同相对湿度下储存。对于这些物理混合物，发现只有当环境相对湿度超过RH(0mix)时蔗糖才会发生水解。降解动力学与储存相对湿度相关，在较高相对湿度下最快。此外，最初观察到一个滞后期，对于储存在接近RH(0mix)的样品最为明显。当暴露于低于RH(0mix)的相对湿度下时，在实验时间段内未检测到蔗糖降解。总之，潮解性固体混合物在较低相对湿度下表现出增加的水吸附，这导致固体溶解并随后导致化学反应性增加。
