Abstract
The sorption of water vapor by the sodium salts of ampicillin, nafcillin, ceftriaxone, cefazolin, piperacillin, cefotaxime and cefuroxime at 24, 34, 44 and 54°C was studied at vapor pressures between 5 and 100 torr by a new method (Hansen et al., 1996). Piperacillin absorbs water at all temperatures and vapor pressures studied. Cefuroxime and cefotaxime did not react. All the other compounds exhibited behavior consistent with formation of a new phase at some critical water vapor pressure, P cH 2O. Enthalpy changes for the water sorption reaction are calculated from a van't Hoff treatment of the P cH 2O values. The thermodynamics of phase changes resulting from reactions of these compounds with water is discussed. The rate of water sorption is a linear function of the water vapor pressure at partial pressures above the equilibrium vapor pressure over the hydrated phase. Kinetics of water sorption as a function of temperature were measured. The activation energy for water sorption is approximately zero.
Published Version
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