Determination of the solubility of a monomer in water by multiple headspace extraction gas chromatography

In water‐based polymerization (suspension, microsuspension, emulsion, miniemulsion, and microemulsion polymerization), the solubility of the monomer in the aqueous phase can have profound effects on the final polymer product. This article demonstrates a novel method for the determination of monomer solubility in water with headspace gas chromatography (GC). In this method, an excess amount of an organic solute of interest was added into a closed headspace vial containing a given volume of water. The organic solute and water in the vial was well mixed by strong hand shaking; then, the equilibrated vapor solute in the vial at a desired temperature was measured by headspace GC with a multiple headspace extraction mode. In each headspace extraction, a part of the vapor phase in the vial was vented for GC analysis and replaced with an inert gas. The excess amount of solute in aqueous solution was eventually removed from the vial after multiple headspace extractions, and the solute concentration in water reached its saturation point. After that point, the concentration of the solute in the vapor dramatically decreased in each subsequent headspace extraction. By plotting vapor concentration versus headspace extraction number, we determined the transition point. The vapor concentration at this point corresponded to the solute solubility, which was calculated through a calibration. This method was very simple and automated; it could easily be used for organic solute solubility measurement at an elevated temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1296–1301, 2006