Browsing by Subject "Hygroscopicity"

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    Hygroscopicity of pharmaceutical crystals.
    (2009-01) Chen, Dabing
    The active pharmaceutical ingredients (APIs) as well as excipients in a solid dosage form can take up water vapor both during manufacture and subsequent storage of the product. Uptake of unacceptable amount of water can cause adverse effects on physical and chemical stability of APIs and functionality of excipients. It is prudent to select drug candidates with low hygroscopicity to minimize the development risk and time. The objectives of this study are: (i) to investigate the risk in predicting long-term water uptake from short-term water sorption studies, (ii) to understand the thermodynamic and kinetic factors that affect water uptake by pharmaceutical crystals. Automated sorption microbalance (ASM) is often used to determine the hygroscopicity, in which the small sample size and gas purge are believed to accelerate the water sorption process so that equilibrium could be attained in a short time period. However, caution must be exercised when the rates of water vapor diffusion or heat transfer at the solid-vapor interface are not the limiting factors. Four cases are discussed in this thesis, in which ASM failed to predict long-term water uptake. 1) Water vapor was believed to diffuse into the lattice of a metastable crystalline form and induced a polymorphic transformation. The crystallization of the stable form led to a decrease in water content. 2) Adsorbed water formed a surface solution and enhanced the mobility of surface molecules. Nucleation rate of hydrate could be the rate-limiting step. 3) Water sorption induced a crystal to liquid crystal transformation in a surface-active compound, where the latter retains orientational but lacks positional order of molecular packing. 4) The formation of a metastable liquid crystalline phase was kinetically favored for amorphous materials formed in surface-active compounds. The metastable liquid crystalline phase was stable for 3 months when stored under ambient conditions.
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    Predicting Influence of Relative Humidity (RH) on Low-Cost Particulate Matter Sensors (LCPMSs) with Empirically Derived Single-Parameter for Hygroscopicity based on K-Kohler Theory
    (2022-12) Tejada, Rayan
    Low-cost particulate matter sensors (LCPMSs) could provide significant insight into air quality data with their ability to be placed virtually anywhere, short sampling time, and cost to build. However, LCPMSs are also known to significantly overestimate particle counts when the relative humidity (RH) is above 65%. It is widely considered that the hygroscopic growth of aerosols is the cause. Hygroscopicity of PM can be described by a single parameter, symbolized as K, and was used in a previous study (Di Antonio et al., 2018) to correct LCPMS data with promising results. However, the study assumed ambient PM to be a pure substance, however, it is often found to be a complex mixture of organic and inorganic chemical species. This study tested if a statistically derived empirical value of K, referred to as “ambient K”, could improve representing the RH influence on LCPMSs. Ambient K is defined as the statistically best-fitting value for several experimental observations of hygroscopy and makes no assumptions on the number of species in ambient PM. Ambient K was graphically demonstrated to be more representative of the experimentally observed RH error compared to assuming K, while having the same statistical performance as conventionally assuming K. Varying observations of hygroscopic behavior among multiple sensors provided strong evidence of multiple chemical species in the observed ambient PM.