Adsorption of Inhalation Anesthetics on Activated Carbon in Humid Atmosphere

Abstract

Halogenated ethers, especially fluranes, are commonly used as inhalation anesthetics in medical treatment of humans and animals. As they pose a health risk to clinicians and have a significant effect on global warming, separation from indoor air in hospitals is desirable. This paper presents adsorption isotherms for desflurane, isoflurane, and sevoflurane at 25 °C on activated carbon D47/3 at 1 bar under a dry and humid atmosphere. Trace level flurane concentrations between 50 and 500 ppm and relative humidities between 10 and 50% were investigated. A magnetic suspension balance and a flame ionization detector were used to determine the loading of flurane and water simultaneously. The results show that the higher the relative humidity, the lower the adsorption capacity of activated carbon. We show that coadsorption of fluranes and water is dominated by the molecular size, polarizability, and polarity. This results in limited pore accessibility of fluranes, dispersion interactions of fluranes and the carbon surface, and polar interactions of fluranes and water. From the isotherm data we derive mechanistic effects like blocking of adsorption sites by preadsorbed water, displacement of adsorbed water molecules with increasing amount of flurane, and cluster formation of water. We propose a mechanistic model to describe these effects. Whereas desflurane and isoflurane displace water and reach their pure-component loadings at higher concentrations, sevoflurane is not able to do so. Water adsorption strongly benefits from adsorbed fluranes with an initial steep increase in water capacity and a subsequent displacement of water with increasing flurane concentration.