Measurement of aqueous Henry's law constants for oxygenates and aromatics found in gasolines by the static headspace method

Abstract

A simple equilibrium vessel made from a large stopcock was used in conjunction with the static headspace method to measure the aqueous Henry's law constants for methyl tert-butyl ether (MTBE) and other potential oxygenates as well as certain of the aromatics found in gasoline. The present method involves using only one aqueous solution whose concentration is not necessarily known. The only quantity that must be known is the phase ratio. Plotting a series of peak areas of the analyte in the headspace after each equilibrium change against the initial peak area of the analyte found in the headspace leads to a linear relationship whose slope is dependent on the analyte's unitless Henry's law constant and the phase ratio. This new method is found to yield unitless aqueous Henry's law constants in the range from 0.02 to 0.2, which are especially applicable to the oxygenates and aromatics found in gasolines.