Mechanisms of halothane adsorption by dry soda-lime

Using fresh soda-lime (15% water by weight) the soda lime/air partition coefficient of halothane was found to decrease as a function of vapour phase halothane concentration from 2.40 at 0.3% halothane by volume to 1.15 at 2.6%, but adsorption generally followed Henry's law. However, soda-lime dried to a constant weight and subsequently exposed to various concentrations of halothane adsorbed approximately 320 microlitre of vaporized liquid halothane per 100 g before a measurable concentration of halothane was detected in the vapour phase. Adding additional halothane then caused a linear increase in vapour concentration. We conclude that dry soda-lime can absorb large quantities of halothane by a mechanism which is similar to that of a molecular sieve. After these "high affinity" sites are satisfied, additional halothane is absorbed by a mechanism following Henry's law.