MEASUREMENT OF WATER-HEXADECANE PARTITION-COEFFICIENTS BY HEADSPACE GAS-CHROMATOGRAPHY AND CALCULATION OF LIMITING ACTIVITY-COEFFICIENTS INWATER

A very simple and easy method for measuring water-hexadecane partition coefficients (P(w,16)) of a wide range of solutes (log P(w,16) rangin g from -2.7 to 4.4) by headspace gas chromatography has been developed . This method requires no standard solution of the solute and no calib ration of the detector. It only requires that the solute be volatile e nough to be measurable in the headspace of the water-hexadecane two-ph ase system and the detector be linear. The precision of measurement is often better than 2% in log P(w,16). From the measured water-hexadeca ne partition coefficient and gas-hexadecane partition coefficient (log K16), a gas-water partition coefficient and hence the limiting activi ty coefficient (gamma(infinity)) in water can be calculated. The gamma (infinity) values obtained this way compare very favorably (ca. 5%) to those directly measured by other techniques such as direct headspace gas chromatography and inert gas stripping. This method should be equa lly applicable to the measurement of partition coefficients between ot her immiscible solvent systems.