An improved method of determining vapor-liquid equilibria for dilute organics in aqueous solution

Chromatographic quantitative analyses of aqueous samples containing dilute concentrations of organic solutes are frequently confounded by sorption phenomena, particularly for vapor samples and aged syringes. A novel apparatus was developed for overcoming this problem; it utilizes continual circulation of gas through a thermostated syringe for sampling, followed by a needleless injection into the chromatograph. Precision and reproducibility well under 0.5% can be obtained in this way. This method was applied to a determination of the solubility of isopentyl acetate in water (2600 ppm) by following the equilibrium vapor response for increasing liquid concentrations. It was also used to determine equilibrium partition coefficients for C1-C5 n-acetates between air and water, over a range of temperatures from 25 to 40 degrees C.