Gas chromatographic measurement of volatility of herbicide esters

The vapour pressures of eleven herbicide esters were calculated from gas chromatographic measurement of relative retention volumes (dibutyl phthalate = 1) on a non-polar SE-30 column. Measurements were made at temperatures from 72 to 182 degrees C, but by assuming that the ratio of the latent heat of vaporization of the ester to that of dibutyl phthalate was independent of temperature, values for vapour pressure could be extrapolated to 25 degrees C. Vapour pressures at 25 degrees C ranged from 2.5.10(-4) mmHg for 2,4-D ethyl ester to 1.9.10(-7) mm Hg for picloram isoocytly ester.