The gas saturation method for vapor pressure measurement is based on the saturation of a carrier gas stream with the vapor of a condensed phase. The vapor is stripped from a measured volume of the saturated carrier gas, the amount of vapor is determined, and the vapor pressure is calculated by assuming ideal gas behavior. One advantage of the gas saturation method is that impurities have a small, predictable effect on the measured vapor pressure. In our recently constructed apparatus, the carrier gas (N<sub>2</sub> or SF<sub>6</sub>) flows through a series of eighteen “concatenated” saturator-adsorber pairs. In this way it is possible to make eighteen simultaneous vapor pressure measurements. An important advantage of the concatenated approach is that it allows for procedures that help to ensure data quality. For example, simultaneous measurements on a control sample (with a well-known vapor pressure curve) are easily implemented. If measured values for the control compound(s) are the same as reference values, within experimental uncertainty, one has additional confidence in the data collected simultaneously for the other compounds. Additional strategies are necessary in order to measure the vapor pressure of compounds with poor stability. In such a case, the repeatability of measurements is an important indication of a successful measurement. For oxidatively unstable compounds—such as unsaturated fatty acid esters—we tested the influence of low concentrations of antioxidant stabilizers on the repeatability of measured vapor pressures. In some cases, the presence of an antioxidant allowed for a successful measurement.

Concatenated gas saturation method for vapor pressure measurement: A technique for oxidatively unstable compounds

249th National Meeting (2015)

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