Ambient Volatility of Triethyl Phosphate

Although deviations are common, the effect of humidity on the volatility of materials is predictable using Raoult's law. This report details the measurement of the effect of water vapor partial pressure on the volatility of triethyl phosphate (TEPO), which has been used as a testing surrogate for G-type nerve agents. The results are compared to similar work for dimethyl methylphosphonate, in which its volatility was suppressed beyond what was predicted by Raoult's law. The current work shows that the effect of humidity on TEPO volatility is nearly as predicted by Raoult's law, that is, vapor pressure suppression is proportional to ambient relative humidity. An empirical correlation taking into account nonideal behavior was developed to enable estimation of TEPO volatility at any combination of ambient temperature and humidity and compared to predications based on Raoult's law. These predictions may be used to support testing using TEPO with a variety of applications, including weapons effects and protective equipment.