GEA-NUS Pharmaceutical Processing Research Laboratory, Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore, 117543, Singapore.
Department of Applied Physics, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, 91904, Jerusalem, Israel.
Pharm Res. 2017 Dec;34(12):2675-2688. doi: 10.1007/s11095-017-2252-x. Epub 2017 Sep 5.
This study explored the potential of combining the use of moisture sorption isotherms and dielectric relaxation profiles of starch and sodium starch glycolate (SSG) to probe the location of moisture in dried and hydrated samples.
Starch and SSG samples, dried and hydrated, were prepared. For hydrated samples, their moisture contents were determined. The samples were probed by dielectric spectroscopy using a frequency band of 0.1 Hz to 1 MHz to investigate their moisture-related relaxation profiles. The moisture sorption and desorption isotherms of starch and SSG were generated using a vapor sorption analyzer, and modeled using the Guggenheim-Anderson-de Boer equation.
A clear high frequency relaxation process was detected in both dried and hydrated starches, while for dried starch, an additional slower low frequency process was also detected. The high frequency relaxation processes in hydrated and dried starches were assigned to the coupled starch-hydrated water relaxation. The low frequency relaxation in dried starch was attributed to the local chain motions of the starch backbone. No relaxation process associated with water was detected in both hydrated and dried SSG within the frequency and temperature range used in this study. The moisture sorption isotherms of SSG suggest the presence of high energy free water, which could have masked the relaxation process of the bound water during dielectric measurements.
The combined study of moisture sorption isotherms and dielectric spectroscopy was shown to be beneficial and complementary in probing the effects of moisture on the relaxation processes of starch and SSG.
本研究探讨了结合使用淀粉和交联淀粉（SSG）的水分吸附等温线和介电弛豫谱来探测干燥和水合样品中水分位置的潜力。
制备淀粉和 SSG 样品，干燥和水合。对于水合样品，测定其水分含量。使用频率范围为 0.1 Hz 至 1 MHz 的介电光谱法探测样品的水分相关弛豫谱。使用蒸汽吸附分析仪生成淀粉和 SSG 的水分吸附和解吸等温线，并使用 Guggenheim-Anderson-de Boer 方程进行建模。
在干燥和水合淀粉中均检测到明显的高频弛豫过程，而对于干燥淀粉，还检测到另外一个较慢的低频过程。水合和干燥淀粉中的高频弛豫过程被分配给淀粉-水的耦合弛豫。干燥淀粉中的低频弛豫归因于淀粉主链的局部链运动。在本研究中使用的频率和温度范围内，在水合和干燥 SSG 中均未检测到与水相关的弛豫过程。SSG 的水分吸附等温线表明存在高能自由水，这可能掩盖了介电测量过程中结合水的弛豫过程。
水分吸附等温线和介电光谱学的联合研究在探测水分对淀粉和 SSG 的弛豫过程的影响方面显示出有益和互补的作用。
