The hygroscopicity of water soluble organic compounds (WSOCs) plays an important role in many applications such as pharmaceutical and food industries and atmospheric science. Unfortunately, most work on hygroscopicity has been focused only on inorganics. In this project, the equilibrium water sorption and desorption characteristics (i.e., the water cycle) of a series of WSOCs using an electrodynamic balance (EDB) was studied. In the EDB, a combination of AC and DC fields is used to trap and levitate a charged particle. The mass of the particle undergoing evaporation or condensation is proportional to the DC voltage required to balance the particle stagnant. The WSOCs studied include four respiratory drugs (atropine sulfate (AS), isoproterenol hydrochloride (IPHC) and isoproterenol hemis...[ Read more ]

The hygroscopicity of water soluble organic compounds (WSOCs) plays an important role in many applications such as pharmaceutical and food industries and atmospheric science. Unfortunately, most work on hygroscopicity has been focused only on inorganics. In this project, the equilibrium water sorption and desorption characteristics (i.e., the water cycle) of a series of WSOCs using an electrodynamic balance (EDB) was studied. In the EDB, a combination of AC and DC fields is used to trap and levitate a charged particle. The mass of the particle undergoing evaporation or condensation is proportional to the DC voltage required to balance the particle stagnant. The WSOCs studied include four respiratory drugs (atropine sulfate (AS), isoproterenol hydrochloride (IPHC) and isoproterenol hemisulfate (IPHS) and disodium cromoglycate (DSCG)), three model additives in pharmaceutical formulations (glucose, citric acid and sorbitol) and nine atmospheric WSOCs. Measurements of the drugs were made at 37℃ and those of the model additives and atmospheric WSOCs were made at 25℃. Combining the bulk water activity (a_w) measurements with the EDB measurements, the equilibrium relationship between particle composition and a_w of each species was obtained. The growth ratios of the WSOCs were also estimated.

Compared with typical inorganic species which exhibit efflorescence and deliquescence in the water cycle, most of the WSOCs studied (all the pharmaceuticals, additives and some atmospheric species (sodium malonate and sodium maleate) studied) do not effloresce nor deliquesce. They sorb and desorb water reversibly in the water cycle. The other atmospheric WSOCs (sodium formate, sodium acetate, sodium succinate, sodium pyruvate and sodium methanesulfonate (Na-MSA)) demonstrated similar behaviors as typical inorganic salts. Residual water exists in the particles of some species when RH is very low. In most cases, the solid states of single particles resulted from crystallization of supersaturated droplets do not form the most thermodynamically stable state found in bulk studies. The findings of this project clearly show that many WSOCs can be as hygroscopic as typical inorganic species but they also have hygroscopic characteristics very different from those of inorganic deliquescent species.